Assembling the Microbee MultiROM

So I have finally got a design for a “MultiROM” ROM changer suitable for use with the PC 85, capable of fitting in a standard case in the ROM H position at IC 22.

https://github.com/cheshirenoir/BeeMultiRom

Assembling these is a little non standard so here’s a guide.

You will need:

If your pins are in a socket or strip, use a sharp set of cutters and cut them out of their housing. These should drop right into the PCB in the wide holes. Fill all the wide holes.

Here I am breaking up sockets. I have stopped using this type so I have plenty to spare.

Once you have filled all the wide holes, insert the spare socket into the top of the turned pins. This will aid in soldering.

Ignore the “extra” pin.

Flip the board over and solder in all the pins. Remove the socket once complete. If your socket isn’t as long as your pins, you’ll need to add more pins and move the socket.

Once all the pins are soldered in, cut the thin part of the legs off them. Yes, it feels criminal, but we’re using these as sockets, not as pins.

Next we solder in the header strip in the next row of holes, poking down. If you’re using the same strip as me, the default length will be fine. If you’re using something else, be careful with your lengths. If you make them too long, you won’t have enough room to close the lid. Too short and you might hit the socket.

The rest of the components can be added in now. Don’t forget the resistor pack has a polarity. Make sure the dot matches the square pin.

Note the square pin for the Resistor array.

Add your 27C2001 ROM in after programming in images. You have 16 x 16k ROM images in there. Or 32 x 8k ROM images. Or a mix, as long as you keep everything aligned to 16k boundaries. (If you have 8k ROMs, they can be accessed by either PAK4 or PAK12 commands. If you have 16k ROMs, they can be accessed by PAK4)

Finally the bit I have to leave a bit open. This is the hex encoder. There are SO many options here. I’ve tried this and this. Neither is perfect. The first feels flimsy. The second only supports 10 positions, and is too big to actually fit in the case. Either way, you connect the “common” pin of your encoder to pin 1 and 2-5 to the remaining pins. You could probably even rig up a 4 way DIP switch by wiring all the pins on one side together then to pin 1 on the connector. Then connect the other side to pins 2-5.

I am currently using the second encoder option.

Not a Soldering Iron in Sight

Updates

Starting with an update on existing projects, I have the Amiga MIDI project working. I’d accidently crossed the input and output lines on the MAX2323 chip. A quick bodle later and it was working. It’s now corrected in the master PCB.

Bodge wires ahoy.

I also have permission from Grzegorz Kraszewski to release my version. That was very kind of them. Please note ALL support for my version is through me. If you want a better MIDI device than mine, go and buy theirs. It’s much smaller and does MIDI IN too!

MIDI playing from a free player. Haven’t yet got MIDI working in any games.

I also purchased some proper IDE to CF adapters from RetroKit, who was kind enough to hand deliver them to me. Helps we work across the road from each other :-D. These were able to finally solve all my IDE issues with the Amiga 600. It’s much neater in there now.

I also finally got around to testing the IDE Buffer board for shorts.
It uses really small components, so checking is a challenge, but I wanted to make sure I had no shorts on adjacent pins.
Unfortunately I did have a short on two pins.
I inspected carefully and it looked fine but the two pins were definitely shorted.
In desperation I checked the schematic… The two pins are both pulled to ground. They’re supposed to be “shorted” together

Oops!

This will get installed in my Amiga 1200, when it’s finished.

PCBs

Onto what I spent most of the last fortnight working on: PCBs!

I use KiCAD a lot these days. I regularly design new circuits and systems. I’m not very good at basic electronics, but transcribing a schematic and generating a PCB, I am getting much better at. This week I ordered no less than 8 different PCBs and designed a ninth, just for giggles. More on that later.

PCB 1 was a new spin of my Amiga MultiROM adapter, designed to take a 27C160 for four different ROM images. Not much to this one. My last spin almost worked. I’ve really only enlarged the pin holes slightly.

PCB 2 is a board for my MegaDrive to Atari joystick. I’ve designed it to fit inside a standard jiffy box from Jaycar. Once it’s done, assuming it works, I’ll be programming in extra features like auto fires and step modes. It’s also got a programmable 3 colour LED now, and a switch so I can change it from Atari 2 button to Amiga 2 button. I’ll probably hard code each adapter to be either Amiga or Atari, rather than switching them.

PCB 3 is a replacement for three different PCBs I’d designed for my Amiga 1200 case build. (Foreshadowing!) This one allows use of either a PS/2 or PS/2 compatible USB Keyboard, a PS/2 compatible USB Mouse plus a joystick (Switchable) plus a standard joystick, all with cables run to the back of the system so you don’t have to reach to the back to plug things in.

PCB 4 is the latest version of my BeeMultiROM switcher, allowing a ridiculous sixteen different ROMs to sit in a single ROM socket on a Microbee. This one is a low profile board, designed to drop inside the case.

PCBs 4-8 are the next version of my CreatiVision controllers.

There’s the button board, with SMD diodes on the back

There’s the joystick lower board,

The disk that sits on top of the joystick board and makes connection when the joystick is moved…

And finally fire buttons (Not shown)

All in all, this has been a momentous amount of prepping, checking, correcting and finally submitting. Hopefully some of these will work, at least. It’d be awesome if I can get at least one of my joysticks working again.

Finally there’s the PCB I’ve designed but have not submitted, mostly because it’s not really a serious product at this point: The CreatiVision Mechanical keyboard!

This was largely done as a bit of a joke. Effectively, if it worked, it would be a full mechanical replacement keyboard, using Cherry MX Switches, with proper stabilisers and the works. The CreatiVision keyboards are notoriously bad. Worse than ZX 81 bad. The “upgraded” keyboard was barely on par with the Sinclair Spectrum “Dead Flesh” keyboards of the day, so the idea of having a fully mechanical keyboard is just silly and appealing. Unfortunately, it’ll cost me about $100 to get just the parts, and even then, there’s no guarantee it’ll work.

Anyone want to sponsor me? 😀

CorelDRAW Work on the Amiga 1200 case

I also spent a week designing the new case for my Amiga 1200. When I purchased it, it was in a beaten up and badly yellowed “Tower Conversion” case. I had designed a new case for it several years ago, but when I recently tried to cut it at the Artifactory, I discovered I could no longer reliably cut 12mm MDF, so I had to redesign. This gave me a chance to remove some of the more… garish flourishes I’d added to the first version.

This was not a small project, and I’ll still need to make a test version, hopefully with an aim of keeping anything that “works” into the final revision, with an aim of cutting less and less each week until I have my final case built.

This is the “skin” of the Amiga, folded flat. The “real” case has bits tucked under and around other bits, so it’s only really there to give you the general idea

Another Productive Break

So, having a week off, I decided to move on a few projects. While not completely successful, I did make some good breakthroughs.

Leading up to the break, I started a repair on a huge old CRT TV, It’s not working… yet but I think I just need to check some things on the inside again. It’s such a heavy beast, I don’t get much time to work on it unfortunately. I did replace a rather bulgy capacitor.

Bulgy boi

I’ve also been building up the Retro Chip Tester for the Artifactory. I’m now short only some key transistors, so that’ll be pending yet another order to one of the big online component stockists.

CreatiVision / Dick Smith Wizzard

On the break, one of the things I did was test a theory I had developed, looking at the CreatiVision (CV from now on) schematic. The biggest problem with replacement controllers of the CV is that all the buttons work by shorting out 3 pins on the controller. This is difficult to simulate as double pole, single throw momentary switches are as rare as the proverbial rockinghorse drops. In my searching I was able to find exactly one switch, which wasn’t cheap, even in bulk.

I’d looked into replacement membranes, which would bypass a lot of the issues, but we needed a minimum order that was much larger than the potential number of buyers. Ah the problems of rare and obscure systems 🙂

It was well known that, realistically, all switches were connected to one pin on the connector, except 2 buttons connected to a second pin. Looking at the schematic, however, I noticed that leading out of the controller, there was a diode on all the pins except the “common” pin. This suggested that I may be able to substitute a simple single pole single throw momentary switch (eg. the most common type of momentary switch out there, ranging from ultra low profile micro tactile for a fraction of a cent each across to exotic keyboard switches costing several dollars each) with a pair of diodes on the two input lines in line with the switch. The idea being that, when bridged, the signal can flow through the switch into the output line, but the diodes means the signal can’t flow backwards across the connection to register “ghost” connections on other lines.

The original sketch of my diode “fix”

I posted my theory on the appropriate forums and got some feedback from TOM, who is much more knowledgeable about these things, suggesting a Shottky diode may work better if normal diodes didn’t work.

I scrounged up some bits and pieces and built up a proto board with two buttons and some standard signal diodes. This didn’t work. Undeterred, I waited to get to the shops and tried again with Shottky diodes and… it actually worked! This changed everything. My setup was only able to press two keys, but they both worked independently. I spent several gleeful minutes typing “2”, “4” and variations (“24”, “42”, 224″, well you get the idea)

“2” “4” “2222” “4444” “2244” “2424” and so on.

Suddenly we could build keyboards with whatever buttons we wanted. I had ideas.

Currently I’ve been working on a simple schematic design, all SMD for space reasons, designed to drop in as replacements for the membranes. I’ve also worked out a design to replace the joypad part, using a thin, flexible PCB with etched on contacts that I want to try. Best of all, I can test a part before moving onto the next part. Hopefully I’ll end up with a design that can replace the innards of the entire controller.

Also, because I can, I have started designing a mechanical keyboard built around Cherry MX keys for that super deluxe typing experience.

Amiga 600

I still had a day or two spare, so I built up a PCB I’d designed, this one an Amiga MIDI board, based on the RastPort KA12.

Once I had it assembled, I needed to test it somehow, so I decided to finally bite the bullet and see if I could get my Amiga working with a CF Card as a substitute hard disk. I had a huge stack of old CF cards I’d salvaged from a variety of places. I had an IDE to CF adapter I’d purchased from AliExpress, so I thought I was ready to go.

I started working through the install process. This is one of those statements that hides a lot. Initially, I plugged in each CF card, booted an Amiga Install 3.1 disk (Thank you Cloanto, for including this with the copy of Amiga Forever I purchased off you!) and tried loading HDToolbox.

I ran an emulator to get these screenshots, but used a real CF Card for accuracy.

Once in HDToolbox, I’d highlight the CF card and click “Change Drive Type”. On the next “Set Drive Type” screen, I’d click “Define New…”

On the “Define/Edit Drive Type” screen, I’d hit the “Read Configuration” button, then “Continue” and one of two things would happen.

Yes we want to continue!

If the CF Card was an Amiga compatible one, I’d get a reading of the details of the drive.

Ah that well known drive brand “CACTUS”.

If the card wasn’t compatible I’d get an Error 7 “Not a Hard Disk”. It would go back into the stack for other uses.

Ruh Roh.

What was happening at this point is I could set up the partitions to my heart’s content, but no matter what I did, I couldn’t get the drives to be recognised on reboot. Thus, I couldn’t format them.

Partitioning

I’d made sure to set the MaxTransfer to the “magic” 0x1FE00 value required by CF Cards. Whatever I did, I couldn’t get it to work. Oddly, I was even able to install an operating system by running HDSetup. It would go through auto-partitioning and formatting the drives, but the drives wouldn’t be visible on the next reboot. Maddening!

In desperation, I even set up the CFs in WinUAE. They wouldn’t be recognised. I could see the drives in HDToolbox, but I couldn’t get them to be recognised. Trying to eliminate potential issues, I even tried the SD Adapter from my Amiga 1200… which worked.

So that eliminated the A600 itself. At this point I looked through my various parts bins and was able to jury rig a different type of CF Card reader, one designed for use in Laptops. I was able to use a 44 pin 2.0mm pitch female IDE to 40 pin 2.54mm pitch male IDE adapter that had come with my Amiga 1200 to plug into the onboard IDE port on the A600. I also needed to splice in a power supply patch as the adapter needed a floppy style Berg connector for power.

To my surprise it actually worked, and I was able to fully install Workbench. All done and dusted, right? Well, no. Turns out the whole thing was stacked too high for me to be able to close the case. Argh!

Next day I went town to Jaycar and purchased a 40 pin IDC connector and modified one of my 44 way 2.0mm IDE cables I had on hand to have the wider 40 pin 2.54mm connector on one end. I simply cut off one end of the cable then splayed out the wires and carefully crimped on the wider connection. Very proud of my work, I went to fit it, only to realise I’d made a cable with the wrong end on it. I had a female end and needed a male end. Oh well. I’m sure I’ll find a use for it.

Digging deep in my parts bins I managed to find a “solution”. One, I might add, that I’m not exactly proud of :-D.

It consisted of:

  • A short 44 pin 2.0mm pitch female to female cable plugged into…
  • A 44 pin 2.0mm pitch male to male adapter plugged into…
  • An adapter with 44 pin 2.0mm female to 40 pin 2.54mm pitch male. This is actually connected in reverse of it’s actual design. It’s designed so you can plug a 44pin HDD into a 40 pin IDE cable. This whole thing is plugged into…
  • A CF to IDE card adapter, that has a 40 pin, 2.54mm female IDE edge connector. I can only assume it’s supposed to be plugged directly into a motherboard. I can’t see how else it should be used.

Amazingly this works, and is in active use.

So ugly! Notice the spliced in power lead.

After all this? There was a mistake on the MIDI board. It was never going to work anyway.

Oh well, back to the drawing board 🙂

Not much going on…

Mostly I have been working on building a Retro Chip Tester so I can start diagnosing things faster with the Amigas. This is actually for the Artifactory, but I plan to use it for a bit before I drop it off to them. If nothing else, I want to get through the backlog of 4116 RAM I have on hand.

I also finally bit the bullet and repaired and recapped the CreatiVision / Dick Smith Wizzard. It’d been falling over with a loud buzzing noise and failing colours. Oddly a tap to the top of the case would often fix the problem.

The motherboard in all its glory. The “bad” Capacitor was the largest one on the far left.

Opening it up I proceeded to check voltage levels, and when they seemed fine, I tapped around the various areas near the power supply and was able to consistently reproduce the issue with one particular capacitor. Out it comes!

Oddly, while removing this component, I noticed what looked suspiciously like a dry joint on a nearby capacitor. No idea which one was the problem but the issue was now fixed. I dropped some hot glue underneath both capacitors to help with avoiding vibration.

I also reattached the heatsinks for the 7805 and 7812 voltage regulators. They were fine, but not neat. I’d obviously been in a rush last time.

Finally I cleaned and rebuilt the reset switch mechanism. It was a simple metal dome arrangement, similar to the one found in Atari CX40 joysticks. a bit of scrubbing and removing some disintegrating foam and it’s as good as new.

The Reset switch PCB. Note how crusty those contacts look.

My next project I have just started work on is making a replacement for the controllers for the CreatiVision as mine have completely failed, and all my attempts to repair them have been unsuccessful. The fly in the ointment is they use a unique arrangement where three pins on the connector need to be connected to make a button press. This means DTST switches. Those are as rare as the proverbial hen’s teeth. I may have a way around using diodes, but I need to confirm.

This repair using conductive ink and tiny masking tape strips did not work…

Something to do on the weekend I guess. 🙂

Speaking of things to do on the weekend, I also did some work on building up an IDE buffer for my Amiga 1200. This will allow me to run longer IDE cables with more devices on them.

It’s all SMD, an area I’m not 100% confident at, but I was happy with the outcome of my endeavour.

The diode is there for scale..

For the capacitors I used sharp tweezers and a really pointy soldering iron. For the ICs, I used a knife blade (K) tip and drag soldered them, dragging away from the chip rather than along the legs. The blade meant it was done in two passes.
Also lots and lots of good flux and a really big magnifying glass.

Mutant Bee. Tac 2 Repair

While I work on a special project, I’ve been paused on all but the most basic work.

One project I did do (And had fun doing) was upgrading my Microbee Personal Communicator up to being a PC85b. This was literally just a swap of the top “core” board for the one I had left over from upgrading one of my other Microbees to the Floppy disk model.

The only complication was the system was very flakey, but after following advice from the Microbee forums, I replaced the inter board connectors with new ones from my stockpile of connectors and we were up and running fine.

While I was there I cleaned off all the excess flux residue from the bottom of the board. I’m not sure if it was from the factory or from rework, but this board was horrible. Isopropanol and a really good scrub got it all loose and moving. I then cleaned it up with more iso and tissues.
(My strategy is, once the residue is somewhat dissolved, flood the board with iso from a spray bottle, then drop down a tissue, then scrub the back of the tissue, forcing it into contact with the board. This works really well for sopping up the sticky residue. Learned that trick off Noel, from Noel’s Retrolab)

These were a horrible nicotine colour just from flux residue.

I also picked up a cheap second hand TAC-2 joystick on the weekend. These are built like the proverbial tank. No “switches” here. The directions are connected by a solid metal sphere with the ground wire and directly contact solid brass direction connectors.

Isn’t it a beauty?
The other end of that shaft is the joystick shaft itself. It seems to be one turned piece.

Even the buttons are brass disks held up with a spring.

I cleaned these with an eraser. These are the fire button contacts. About the size of an Australian 20c piece. Or a quarter if you prefer.
Here is a picture of the guts exposed.

Now, apparently something had decided to have a “nibble” on the cable. Rather than attempt to splice in a new cable, I decided to cut out the damage, and connect the two ends together. The cable was nice and fat, and I used glue lined shrinkwrap as a new outer sheath so I’m pretty happy that it’ll hold.

Nom nom nom
Cut, ready for twisting the end, and then joining back together.
Glue lined shrinkwrap. Ready for heat. This stuff is not going to go anywhere. I also shrinkwrapped each wire as well after joining.

What Next?

I’m in a contemplative mood today, and I’ve been thinking about my collection. Specifically I have been thinking about what I want to get next. Here are my thoughts.

Computers

At this point I am really not going out of my way to buy any more computers with two exceptions. If someone offers me a system, obviously I will contemplate it seriously. I’m just not going to go and hunt down systems any more. No more eBay searches. No more trawling through message boards.

The two exceptions are:

  • The new Microbee – Ewan at Microbee Technologies is slaving away on a new “Premium Plus” Microbee. I want one. I just hope I can afford one at the time :-D. I may go into debt to get one.
  • A Sinclair Spectrum 128k clone – I really enjoyed building the Omega MSX2, and another “kit” computer sounds awesome fun. The Harlequin 128K would fit the bill, but I am also looking further afield at more exotic versions of the Spectrum 128k.

Consoles

At this stage, I want three more consoles. There’s a fourth I will add to the list as a “It’d be nice to have” but I’m not as desperate for that as for the other three. Other consoles I would probably accept, but I’ve got most of the ones I am desperate to play.

  • A Super Nintendo Entertainment System – It’s a classic. An icon of its time, and has a library full of games I want to play, and to play again. Super Mario RPG FTW.
  • A PC Engine – The littlest console that could! The powerhouse from Japan. The coolest console I never got to play. I remember seeing reviews of these in computer gaming mags at the time it came out. The performance was mindblowing. Do want!
  • The Atari 7800 – The best of both worlds. Able to play both Atari 2600 games and Atari 7800 games. It scratches my Atari itch. Also the controllers are not bad.
  • (the nice to have) Sony Dreamcast – I nearly got one of these. They have a decent library of games and are easy to mod.

Addons and Upgrades

There are a lot of these. Even after the “year of the peripheral”, there are more to get. Mostly around making my existing systems easier / more fun to use.

  • Hummingboard for the Apple II – Sound at last for the old beeping beast.
  • “Everdrives” for the consoles – A way of playing the games I want to play, when I want to play them. NES, SNES, PC Engine, Atari 7800. to name a few
  • An “All in One” cart for the MSX – There’s a variety of these. Most emulate cartridges, add more RAM and add additional sound capabilities.
  • A HDD solution for the Atari STs – ACSI2STM would probably fit the bill.
  • A case for the A1200 – Sigh. I need to revise my cutting file for this and get off my bum and actually make it.

Going for some doubleyous, boys.

(Obligatory Letterkenney reference now complete)

So it’s a long weekend, and thanks for some confluence of leave, for me it was a four day weekend. Such a nice thing occasionally.

Friday I spent mostly working on general chores, but in the evening I thought I’d finally drag out a project to start looking at. Now I know some of this will be my repair skills getting slowly better and better, but I think there was also some luck because, spoiler alert, things went better than I could have imagined.

Microbee 128K

First on the bench was the ‘bee, which has been vexing me for over a month now. It was not showing any signal on the screen.

Having exhausted what could reasonably be tested based on symptoms, and having applied many weird and wonderful fixes, I decided to “get back to basics” and start from one end of the system and work back. I chose to start at the Z80 CPU, and to check all the pins for activity, just to see “what I could see”.

The schematics for this were incredibly useful, insomuch as they laid out all the important signals, and their pin number in a consistent way.

This is the relevant section of the schematics for the CPU on the Main board.

First up, I had to use my “Core Lifter” boards to raise the Core (Ie top board with RAM, ROM and some controllers) up from the Main board (where the CPU and main I/O chipset lives, plus the keyboard)

Core Lifter boards. Essential for proper Microbee diagnostics.

Setting up the oscilloscope, I started probing down all the “special” pins initially. All the “special” pins are inverted, so active low. Quickly I noticed that while most were held high, or were oscillating, one was being held low, NMI. The Non Maskable Interrupt

OK. that’s not right. That means the machine is being constantly interrupted. It would never get anything done. (NMI is supposed to be pulsed so the CPU knows to go and look for what caused the interrupt.)

Interestingly, I had a suspicion something like this was happening. I thought it might have been the RESET line, but NMI, with hindsight, made more sense.

On the schematics, I traced the NMI line from the CPU across to pin 17 on the connector between boards. Not a problem. I can still see it being held low on the corresponding pin on the core board, so we seem to be getting somewhere.

I removed the “Lifer” boards so I was more easily able to get to the Core board and started following the signals back.

The appropriate part of the Core board schematic

Following the signal on the schematic led me to pin 6 on IC49, a 74HC14 inverter. At the other end of the inverter, I could see the signal was high, so that IC must have been fine (HINT: FORESHADOWING!) so I moved behind that. R12 looked OK and was a weak pullup anyway. IC 41 was a 74LS08 AND gate emitting a high signal. Coming into it was a high signal on pin 5 and a “low” signal on pin 4.

That doesn’t look right. If only one of the pins is high, it should be emitting a low signal.

I get out the desoldering gun (I recently got a new handpiece for this and it makes SUCH a difference!) and quickly had the chip out and straight into my tester where… it passed!

D’oh! Maybe this was one of those cases where the tester isn’t testing properly? I drop in a socket and plonk it back on the board and keep probing around. Something is niggling my backbrain and I can’t work out what it is. I check pins on the next IC back from IC 41, which is another inverter on IC49. I can see a strong low coming into it but… the signal coming out feeding into the AND gate doesn’t look right. It’s riding up way above ground up around 1.5v which is well into the “undefined” area for logic of this type. Maybe here is my problem? I pop it out and whack it in the tester and that inverter fails the test. Whoah. Could this be it?

It was late by this point so I had to wait until the morning before whisking out to the local electronics shop for a replacement. Thankfully they had the component in stock, which was nice.

Getting it home I plugged in the new chip and powered up the ‘bee. Still no signal. D’oh!

I checked the NMI line and it was now behaving itself. I could see activity all over the place on the board… I thought I better eliminate the obvious and tried a different Microbee… which also had no signal. Double D’oh! Fiddling with the video cable and I could see a BASIC prompt picture. Plug in the 128K ‘bee again and I can suddenly see the white block cursor. Excitedly I plugged in the Gotek drive emulator with the right USB stick, powered it up and… IT BOOTED! I was so happy I let out a whoop.

(I also fixed the stupid video cable once and for all. It had got twisted, which had bent a connector, shorting the video signal.)

I did a quick happy dance, and then spent half an hour playing various Microbee games. Finally I screwed the case back on and started contemplating my next thing to fix.

So pretty! I’ll be doing a version in acrylic when I can. Anyone out there own an acrylic wholesaler that would like to sponsor me? 😀

How about something much harder and more vexing?

Acorn Archimedes A440

So I set myself a real challenge this time. This system had been broken for closer to six months at this point, but now I was much more confident about using my oscilloscope and thought it was time to get back “at” it.

On the bench it went and I reviewed where I was up to. It had a repeatable problem where the drive would never be properly seen. It would proclaim “Drive Empty” whether it was a real floppy disk drive or a Gotek drive emulator.

Not happy, Jan.

A lot of people on the StarDot forums thought it had to be IC29, A 74HC574 logic chip (It’s a flipflop. It’s been so long since I did logic at Uni I can’t even remember what that means any more. I should go and do some research) that didn’t seem to be getting the right signal on its select line (pin 11).

Random photo of the inside of the BBC Master system, mostly taken so I knew where the power leads went.

Before I went down that path, I wanted to test my 1772 Disc controller chip in a “known good” computer, so I stripped down my BBC Master, socketed the 1772 in there and tested the chip from the Archimedes, which, of course, promptly passed all the tests. OK, one issue down.

The relevant part of the A440 Schematic

After confirming I was actually using the scope right, I confirmed that, no, the select line was never being triggered. I looked up the schematic some more and pin 11 on IC 29 conveniently connects to pin 11 on IC31, which is a 74HC138. It’s a demultiplexer. It takes 3 binary pins and, depending on the values, selects one of 8 output pins. One of those pins is what’s connecting to IC 29.

So looking at IC 31 under the scope, I can see lots and lots of activity on the three input pins, so some of those output pins should be doing something and… nope. Nothing. Not a cracker. Could this be another easy fix once I knew the real culprit? Quick! Back to Jaycar to grab a couple of 74HC138s.

Plugging one in and powering up the Archimedes, I access the Gotek drive, which promptly lights up and starts reading. Whoop! More happy dances! I go and give my long-suffering wife a big sloppy kiss, before re-assembling the Archimedes.

The rest of the day is spent resetting the Archimedes back up. I have added back in the HDD Podule and even installed and tested a joystick adapter that plugs into the printer port. (I had built this ages ago and it was while trying to test it that I discovered the problems with the Floppy drives.)

Several games of Pacmania followed. (The Archimedes port is simply a stunning version. Possibly the best port I know of. Fast and buttery smooth)

I’ve also used Arculator (An emulator of Archimedes computers) as a bridge to allow me to write software to “blank” ADF floppy files for use with the Gotek.

Currently I have the Amiga 1000 on the bench. Let’s see if we can get that working too?

Some Glue, Some Art

While I have made absolutely no real progress on my Microbee, I did make some progress on the Amiga 500 and the Amiga 1000.

Firstly, the Amiga 1000 is currently booting off Kickstart before dying in its tracks. It’ll boot Kickstart, reboot and then lose synchronization on the screen. Basically dead in the water. At this point I’m fairly sure it’s a memory fault on the “mezzanine” board that Kickstart loads into, but that’s a project for another day.

The mezzanine board his clearly visible here as the raised section central to the picture.

As part of my diagnostics, I removed the internal floppy disk and dropped in a Gotek. Did you know you have to remove twenty nine screws, in six different types to remove the floppy drive? I do now, and I am not looking forward to having to remove them all again later to work on that RAM board 😀

Dear Commodore. Did someone in upper management have shares in a fastener manufacturer?

While I had it apart, I cleaned and lubed the mechanism and carefully cleaned the drive heads. I use Inox grease on anything that touches plastic and white lithium grease on any metal-on-metal parts.

It now seems pretty happy to at least reliably boot the Kickstart, even if it crashes on completion/

The drive internals, during cleaning

Of course the next step was the Amiga 500. That led to a difficult moment where I had to cut a 30 year old “warranty void if removed” sticker. I tried removing it with hot air, but it’s so old, I don’t think there’s any plasticity in the glue any more. Eventually I just cut it as neatly as possible.

After that it was a much more reasonable 9 screws to get the floppy drive out and lube and service it. This one was pretty gummed up, but after some TLC and quite a lot of swearing I got it all cleaned up and it’s now working, albeit not 100% reliably. It seems to need cleaning every second disk. That may simply be old media or the drive may be on its way out. Long term I’ll probably fit a Gotek to the A500, simply because it will make it so much eaiser to use.

I’d worked out a “pipeline” to make new floppy disk images, which was both simple and effective.

  1. Get out an Amiga with a Gotek already installed. In this case that meant the Amiga 600.
  2. Connect the external Floppy Disk Drive to it.
  3. Boot it into a copying suite from the Gotek. I use XCopy Pro. An oldie but a goodie.
  4. Set your copier up to copy from internal to external. (The internal being the Gotek)
  5. Load up the image you want to copy across, make sure you’re set up for a suitable copying solution (I prefer Nibble+).
  6. Insert a blank Double Density disk in the external drive and start your copy.
  7. Once done, clean the external drive.
It works!

With this pipeline, I was able to make a bunch of copies of classic games. After that I decided they needed sprucing up, so I used CorelDRAW and a template to make some floppy disk artwork, suitable for the subject of each disk. I used a mix of cover art and screengrabs with each.

After that it was just a matter of printing them to glossy paper, cutting them out neatly, spraying some workable fixative to the back and et voilà! Disks that look nicer than the originals.

Every time I see that IK+ logo, I hear the theme music in my head.
Custom chips in the A1000
The venerable Motorola 68000 in the A1000

Life Gets in the Way

It’s been nearly a month without a post. While some things have happened in the meantime, not a lot of new developments have occurred.

Microbee: First the bad news

Yeah. That’s not right.

I was supposed to be bringing one of my Microbees to the Perth Amiga Users Group gathering, so of course, I chose the DRAM 128k with the external Gotek…

Of course it decided to fail two days out and I am yet to recover it at this point. There’s been a lot of back and forth on the Microbee forums as to what may be causing the problem but I don’t yet know what the root cause is. I’ll keep looking.

Current symptoms are that when you turn it on, you get no synch on the monitor. If you repeatedly press the Reset button, you sometimes get the “I’m booting” cursor (But no boot) or garbage on screen. If you repeatedly press the Reset button, while holding down M, you sometimes get the Monitor but no characters. I’ve managed to get a RAM test working and the RAM is checking out.

Microbee: Now the Good News

Classy! Pity the desk is such a mess.
Even the back looks good.

The case is finished and it looks amazing! I need to do a final version in clear and smoked acrylic but I am super happy with the way it eventually came out. There is a minor issue, but so minor I’ll correct it without having to cut another test revision.

MSX: The Slow boat

Still waiting for the chip to arrive from China. Hope this one is not a fake…

Amiga 2000: Still Broken

I’ve been doing a lot of probing around and checking on this and I think it’s a problem with the Angus custom chip. I have also borrowed a DiagROM off a friend, but I need to get a null modem cable organised. There’s also another thing that will most likely help with this…

Pickups

…or more accurately drop offs as the person who gave these to me was kind enough to deliver.

So while I was at a local convention, I was approached by someone I have known for many many moons (And would consider a friend) approach me and ask if I wanted some Amigas. Of course I said “Oh yes please!”. She and her partner were downsizing and the systems had been sitting in the cupboard for a while.

Now it took a few weeks for timings to be right and the whole time between the initial offer and the systems arriving, I didn’t want to say anything in case I jinxed things 🙂

(This was particularly difficult at the Perth Amiga Users Group, I can assure you)

But in time, things aligned and my friend dropped off not one, but two Amigas!

Left: Amiga 500, Right: Amiga 1000, Middle: cables, mouses, external floppy drive

These are, respectively, an Amiga 500 and an Amiga 1000. Oddly the 500 is the later (cost reduced) system. I had neither of these systems at this point. There’s also another 1081 monitor, 3 genuine Amiga “tank” mouses and an external floppy drive.

Knowing more than is possibly healthy about these systems by now, I checked, and unfortunately the battery in the RAM expansion on the A500 has rotted out. Thankfully the damage seems confined to the RAM expansion, and, even then, isn’t too extensive. I hope to have the RAM expansion fixed next weekend. I just need some parts.

See that dark green? Corrosion.

The A500 is also running an older version of Kickstart (Think of something like a BIOS, but more feature rich), which I found interesting. It suggests this system must be an early model. Unfortunately, as far as I can tell, the floppy disk drive on it is not working. Might just replace it with a Gotek and be done with it.

About that desk…

There’s also the original factory seal on the bottom of this system, which suggests it’s never been opened, which is amazing in itself.

You don’t see many of these intact

The A1000 has been opened at least once, by me, as some power supplies in these models have RIFA caps, which can explode. Thankfully mine does not have that problem and it’s absolutely fine inside.

Yes it will need some TLC.

The A1000 has an interesting configuration where the Kickstart of the system is on floppy disk, rather than in ROM like later models like the A500. Unfortunately I have not been able to get this one to boot off the provided Kickstart disks. I’m still working on that. One approach I have taken is to use the external Floppy with my Amiga 600, so I can copy files from the internal Gotek to the external Floppy.

The other thing about the A1000 is the custom chips were somewhat unique to this model… and one other model. That’s right! My Amiga 2000! (Later Amiga 2000s had a different chipset. The same one in the Amiga 500)

This means I’ll be able to use the A2000 to test the A1000 and vice versa. Happy days!

This A1000 is also complete. It has the keyboard, the keyboard cable, the front RAM cover and even the strange right angled connector on the Tank mouse. It’s super nice to have such a complete system.

Finally the 1081 monitor works fine, which is nice as these are very capable CRT monitors with SCART out on them.

Hey, the Amstrad was the first computer I could lay my hands on with a SCART cable handy.

My goodness, it’s been a while!

Hi Intarwubs. It’s been a while since my last post. Things have been very slowly proceeding, and then, like unplugging a cork, there has been a huge rush this long weekend.

Updates on the last post

So some quick updates on everything covered in the last post.

Firstly the Microbee ROM switcher is working fine. It always was. Turns out to be user error on my behalf. D’oh! The command to call the upper half of the ROM was PAK12. I was using PAK9. Ironically, by the end of this article I will no longer be using that board.

Secondly I was able to find an actual user manual for the Taxan monitor, and it’s actually a really nice monitor! It’s got RGB plus either H/V synch or synch on Composite. Plus, with the push of a button it becomes a green screen :-). It even has a second connector for CGA or Apple III RGB. That’s a good coverage!
As it only has the one connector for the primary RGB input, I have made a pigtail that ends in the much more common DIN 6 connector. I’ll probably end up using it with my MSX.

Seriously, this is an odd connector. It’s primarily used in high end Japanese video.
Not blurry in real life 🙂
The pigtail

Microbee Disk Conversion

This took a lot of time, but it was so worth it in the end.

For those new to the feed, I had received a “StarNet” Microbee Core board. These were used as network terminals with no local storage. The booted off a local network server as a low cost alternative for places like schools.

The difference between these and the floppy disk units was a handful of chips and a BIOS changeover.

First up was ordering a whole slew of chips and components from all over the world. Some local. Some from China and some from the US.

While I waited for parts to come in, I began soldering in sockets and all the components I had in hand. I already had all the resistors, the variable capacitor and all but one of the normal capacitors.

All the parts I had on hand.

I was able to source on particularly tricky chip (a 74LS06) locally from Artifactory (membership has its benefits) and another I thought I was going to have problems with (a 74LS07), I found while going through my parts bins. (I sort everything by category, but it still sometimes means sifting through dozens of components)

I also did some research and burned myself a suitable FDD Boot ROM to replace the network boot ROM which it came with.

Slowly the parts filtered in and I built up the board. The last bunch of parts all arrived over a period of two days, which was pretty nice.

After that it was simply a matter of soldering in a resistor array, a variable resistor, a lone cap and an edge connector. Then I just dropped all the chips in their sockets.

All assembled.

After some procrastination, I took a deep breath and turned it on and… nothing. Not even synch to the screen.

Sigh.

Well, I do have a fancy new oscilloscope, and thanks to my fellow Artifactorians, I was confident I knew how to use it. I soldered a nice stable earth lug into an empty socket to assist me with my testing.

I decided to start on the address lines on the ROM socket. Immediately I saw data! A series of nice square pulses. That’s a good sign. That means it’s trying to do to something. Let’s check the rest of the pins.
After some probing around A14 on the ROM was held high, but checking the schematic, that was deliberate. Looks like it allowed larger ROMs to be used by tieing up one of the lines so that only half needs to be addressed.
Next I looked at the data lines and while most were fine, Data line D0 was being held low. Hmm. Shorted to ground. No wonder nothing good is happening.

I did some digging and I identified several possible culprits. The first one, the ROM itself, was easy to eliminate as I’d already tested it while writing it. Next was IC35, the WDC2793. This was socketed so was easy to remove and test. Nope. Still D0 held low.

This led, according to my searching, 3 primary candidates: IC29 (74LS175), IC24 and IC 25 (4164 RAM) all hung off that data line according to the schematic.

I jumped onto some forums at this point and asked for help. I knew I had spare 4164 RAM from fixing my Acorn Electron, and I knew I could buy new 74LS175s as well, but I wanted to see if there was anything I hadn’t thought of. I suspected the RAM. I always suspect the RAM (Spoilers: It wasn’t the RAM)

While I waited to see if anyone responded, I got impatient and socketed the 74LS175. It passed testing in my TL866II+ EPROM/Chip tester and the short was still there.

Meanwhile I’d had a response suggesting I also check IC 16 (74LS174) and more tellingly, check around the edge connector as D0 was right next to a ground connection there.

Guess where the fault was? Yep. I’d accidently shorted D0 at the edge connector!

Some short work later and I was getting what looked like a cursor. This was a positive sign! Little did I know HOW positive.

Cursor

Back to the forums I asked what I should be doing next. I was advised to hold down the M key on boot to see if the system got into the Machine Code Monitor. Lo and behold it worked! Amazing! What I thought was the cursor was the system booting but having problems getting to an OS.

The same poster asked if I’d modified the baseboard yet. LOL what? This hadn’t come up as something you could do. I was pointed to a suitable tech sheet, the wonderfully named “Microbee Hardware Notebook” (which is chock full of mods, tweaks and improvements for your ‘bee) which had a whole 2 pages on modding a baseboard for DRAM systems and immediately afterwards, 2 pages on testing the floppy controller.

Modifying the baseboard wasn’t too hard once I knew it had to be done. A simple matter of cutting 3 traces, soldering in a bridge and a single resistor.

Once done, I was able to run the tests on the floppy controller, ready to proceed to my next step.

There was one more hurdle. I needed to make a power supply for the Gotek I planned to use as a floppy drive.

Now, my Microbee already has a stepped down power adapter with a switch in a jiffy box. I figured I could hide a simple 5v 7805 based regulator inside the box, no worries at all. I quickly lashed something together using some experimenter’s board, two spare capacitors, a spare 7805 I had as well as a heatsink off a past project. the whole project was tiny, and snuck inside empty space inside the jiffy box without any issue whatsoever. I ran up a power cable and terminated both ends in 2.54mm headers (Purchased from Altronics in a kit that I an no longer seem to find) which have an added bonus of being compatible with Floppy Drive Berg connectors with minimum modifications, and are a lot cheaper and more readily available. In the box I terminated in a second male connector and the whole thing was ready to go.

The external switch box.
The regulator. 2 caps. 1 7805. A heatsink.
This is the connector that goes to the FDD.

Having checked all the voltages, also for shorts and basically fidgeted for a good 15 minutes, I finally loaded up some Microbee images , plugged everything together and powered it on.

Turns out this wasn’t even that compatible with my Microbee!

I may have sworn at this point. It. Was. Working!

After this, the rest was anticlimactic. There was a slight detour where I tried fitting the whole system in a Microbee case. (Won’t work as the connector is in the wrong place)
I also tried a newer ROM. (Won’t work as I had already chosen the last version that worked in non “premium” Microbees)

I also discovered the disk image I’d chosen to test things wouldn’t work with my model as I’d accidently chosen one for “premium” models. 😀

My Disk based Microbee lives.

LIFE! Give my crea… Wait I think we’ve done that joke.

My next step will be to box this one up in a nice home made case. I have already started work on the next generation of the laser cut case, so that will hopefully be along shortly.

MSX Floppy Disk Controller

This one was started before the Microbee project, but finished afterwards, so apologies for any confusion here.

Similar to the Microbee, this one consisted of ordering a whole bunch of parts and waiting for them to arrive.

Thankfully there were less parts on this one, and most were available locally. As a result I had this project mostly done earlier than the Microbee.

Waiting for parts.

I also had to build up a power cable. Thankfully the Omega works off 5V, which is the same as the Gotek needs so it was a simple job to make a splitter Y cable.

Power splitter.

Everything arrived and I soldered it all up.

Only thing was, it didn’t work. Was it a problem with my Omega or the board? The system wouldn’t complete a boot and the Gotek kept complaining about a cable fault.

Thankfully the build documentation was excellent, even when translated. Super giant hats off to the team that wrote them!

I worked through the steps described, even going so far as to burn out a simple game ROM to try in the cartridge as an interim step. The cartridge ROM worked, which at least confirmed the issue wasn’t the Omega not being able to boot systems.

The next step was to measure the frequency on pin 4 of the 74LS04 in the clock circuit. Out comes the oscilloscope again. Except things didn’t look… right. The clock looked weak and was more of a triangular shape. I wasn’t sure at this point if it was me using my ‘scope wrong or a genuine issue.

At this point I took the whole setup out to Artifactory and the team there helped me confirm that, no, I wasn’t imagining things. The clock was terrible. The easiest thing to do was to compare it to the clock on the Z80 which was a world apart. Clocks should not look like triangle waves 😀

Taking it all home again, I realised I had a spare 74LS04 from a different manufacturer at home in my spare parts bin. In it went and now I was getting a nice square wave clock. Excellent!

Except the system was still not working. I knew at this point that the only thing that could be stopping things working was my FDD driver chip, the WD37C65B-PL. I’d ordered 3 so I tried a different one. The system went wild! Hmm. Tried chip 3. Different behaviour again.

I was suspicious at this point. I took a closer look at the chips. All three had the same manufacturing codes! The chances of that are basically zero.

The lower row of numbers should be different for every chip manufactured. These three are all the same

On a whim I wiped the top surface with some isopropanol on a cotton tip. The top wiped off! These were fakes! I raised a complaint with the supplier.

Cotton tip before and after rubbing chips with iso.

I reached out on Facebook to the local community, and Matt (who I had worked with on his Atari ST) offered to lend me a card with a WD37C65B-PL onboard I could use to test my card. I took up his kind offer and…

Donor board.

Yes! I have a working FDC!

Snaaake!

I’ve ordered another chip from a source I have had good luck with in the past and I will return Matts card to him now I know everything works.

This all needs a case

I also need to work on a case. I’m thinking something acrylic could be nice. That way the purple PCB will show through.

The final card.