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.


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.


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…


…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.


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.


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!


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.

Some new additions, some new repairs

While the last few weeks have been busy, they haven’t been that busy on a retro front.

I realised I’d ordered the wrong Floppy Disk controllers for the Microbee and the MSX controller, so I had to order replacements. They’ll take quite some time to get here, but that’s OK. Due to some financial commitments in my life, I can’t quite afford the many parts to finish either project at this point. This pinch will go away soon and I’ll be able to get a bit more aggressive with my parts purchasing.

As it is I have been able to get quite a lot of parts, only to run out of solder, of all things. Oh well. Next fortnight I guess.

Despite the tight budget, I did get two more systems, thanks to a reader of this blog (Hi Richard!) who has given me his old computer system collection. There’s some really interesting stuff in here.

The Breadbin

The other nickname for these was “Toads”, due to their colouring and general shape.

First up we have a classic “breadbin” Commodore 64. The power supplies on these models have a fatal flaw where the 5V rail will creep up and up and eventually burn out the system, so for now I have put it aside and used my own dedicated power supply.

The inside. Heatsinks applied to major chips to extend life.

On power up it presented a familiar blue screen of happiness. Further investigation, it looks like the SID sound has failed. I have confirmed this by trying the chip in a working system. Down the track I will purchase an ARMSID replacement. It will be nice to have both styles of C64, as my other units are all the later C64c styling. It’s in really nice nick.

The Beeb

Not what I was expecting

When Richard lulled this one out, I was astounded as I was expecting a “classic” BBC Micro Model B, possibly with one or two external drives. This is a much newer and stranger creature. This is a BBC Master Compact. It has more RAM, and the power supply and disk drive have been combined into what’s referred to as the “Monitor Stand”. (It’s the bit underneath the main unit there)

I inspected the power supply and discovered a very mazed X2 RIFA capacitor, so rather than try and power it on, I dug out a suitable power supply from my stash and plugged it in to the main unit.

RIFA cap is the block next to the fuse.

On power up it emitted the long familiar “Booooo Beep!” of the RAM test being completed and the system booting. (If you have ever used a BBC Micro of any type, you’ll know the sound)

Some of the keys weren’t working so I couldn’t test it very far but I was able to write the usual “Hello world” program, albeit without being able to use the SHIFT keys or the space bar. More on that later.

I was able to get to my local electronics store on Thursday evening and purchase a replacement X2 cap. This one is not Mica filled so should have a longer life.

Some quick work with the desoldering gun and out the old cap came and in the new one went, using some of the “scrap” solder I have on hand. (It just needs a bit more flux). I also cleaned up the power supply while I was at it.

The two X2 caps. the cracks are visible in the removed, old capacitor.

I need to mention the faintly bizarre way to get into the monitor stand at this point. As it has mains potential and has some juicy capacitors, it’s all marked as being “no user serviceable parts”. If you need to get in, here’s how to do it:
Firstly the front plastic bezel and the back plastic bezel simply pull off away from the unit. The side plastic bezels rae a lot trickier as they need to pivot on hidden lugs. They pivot on the base so pull from the top. (I was really terrified I was going to crack something in these old brittle plastics but it was fine in the end).
Next there are 4 metal screws on the underside. Once they are gone, the top cover is now free to simply slide off the main unit.

A little bit of research revealed that the keyboard on the Master Compact isn’t a mechanical keyboard like older units, but is a rubber dome system. I opened it up by removing about a million screws, and cleaned all the contacts with isopropyl. For the space bar and the SHIFT keys, I also cleaned the carbon contact on the rubber domes gently with an ink eraser followed by a dab of isopropyl on a cotton bud.

The inside of the Master Compact.

Now everything had either been repaired or cleaned, I gave the system a go and it works perfectly now. I have no plans to upgrade this one at this juncture, although I am eyeing up some internal upgrades to make booting games easier.

The rest of the haul

Richard also provided two CRT Monitors, a printer, some BBC Compact software, a datasette for the C64 and a bunch of cables, dust covers and even a tray hand made to hold the C64.

Looking at the monitors, there’s a 14″ Thompson branded monitor (Model CM 36632 VPR, which I can find absolutely nothing about on Google) with a SCART in. It seems to work OK, for a screen of this vintage. The power button is a bit gummy, so probably needs opening and cleaning.

Next up is a 12″ Taxan (Model KS12R305S-AN, also a mystery on the internet) with a pair of mystery connectors. The cable I have doesn’t seem to match either the C64 or the BBC so I’m at a loss as to what it should plug into.

There was also an Epson LX-800 printer, complete with tractor feed. It’s a parallel port printer, so compatible with several of my systems.

Other stuff

I completed the ROM switcher for the Microbee. It mostly works, insomuch as I can choose a ROM easily enough. Only thing is, the second ROM in each pair is always the same. Not sure what is going on there. I’ll need to research how the bank switching is working.

It works, but it doesn’t work how I expected.

I spun yet another spin of the Microbee case. This one is extremely close to being “right”, to the point that the ‘bee is currently living inside the prototype. There’s some minor tweaking on some holes to be done (There always is), and one of the braces was out by 3mm because I measured its location from the wrong reference point.

Stuff coming down the pipe

So it’s been a while since I did anything major. I did do another spin (My third so far) at the laser cut Microbee case, which revealed I needed to refactor parts of it.

Top View.
The ports all line up, which is nice.
The inside.

I tried to make a fastening system so the upper half and the lower half could be screwed together, but I was too clever by half, and it was never going to work. Thinking about the problem, I came up with a new solution which is dramatically simpler. Back to Artifactory on Wednesday to cut more MDF.

I do look forward to finally being able to cut this from acrylic. I think it’ll look awesome.

Mail Delivery

So I was work from home for a week, and, of course, everything I’d ordered for the last few months finally arrived last week. The last two packages trickled in today.

This will mean I am much more able to continue with some projects. I’m a little limited on free spending money right now, but the components I need should be local and cheap.

By the way, none of the following was sponsored. All purchased with my own $$$. If any one feels like sending me stuff to review, reach out! 😀

This was only the stuff for me. My partner gets stuff delivered to my work too.
Item 1

This first item is an External Floppy drive adapter for the Amiga. I plan to use this to add a second drive to my Amiga 1200 when I finally laser cut the box for it. I plan to use the drive that was the internal drive as the second drive. Purchased from via ebay.

Items 2 and 3

Next up is a pair of PCBs from JLCPCB. The blue one is my own creation. If it works, It’ll plug into a ROM socket on a Microbee and offer 16 different ROM addresses. No idea if it works yet. The theory is pretty simple.

The purple one is an MSX Floppy Drive interface. Can’t wait to get this one assembled! Loading software into the MSX via tape is an exercise in masochism. I will drive this one from a Gotek.

Item 4

Next up are a pair of Floppy disk controllers. These are for the MSX PCB above. I ordered two in case one was a dud. Now I’m hoping both work. More on that in a bit.

Item 5

These are 10 27C256 EPROMs. They’re 256 Kilobit roms. 8 KB each. Also purchased for the MSX project. I have no doubt I will find uses for the other 9.

Last but definitely not least, item 6.

Finally we have the star of the show. This is a Microbee DRAM Core board. These will clip into one of my existing Microbees, upgrading them from 32K to 128K, and also (once populated) add a floppy drive port. This particular core board is out of a Star Network Workstation, so is missing all the floppy drive logic. Guess what? The key chip is the WDC37C65C Floppy drive controller. Have we seen that anywhere? 😀

All in all, there’s only a handful of chips that need adding and a mess of passives. I need to catalog exactly what is missing but i’m hopeful I can either get it all locally.

Once I have it working I plan to add a Gotek to it. After that I think my stash of Goteks will be dry. Oh well. I’ll have to order some more. I got a good run out of the last order of 5.

Upgrading the VRAM in a Quadra 950

So you have a lovely Macintosh Quadra 950 with only the onboard 1MB of VRAM, and you want to upgrade it to the full 2MB? Here’s how.

Firstly you will need 4 sticks of compatible VRAM. These come in either 256K or 512K sizes. While you can use 512K sticks, only 256K will be visible to the system, so a bit of a waste.

Make sure you observe Anti Static precautions for the next few steps. At a bare minimum, make sure you are earthing yourself to the metallic parts of the system chassis while you work. Better yet, use an ESD workstation. (My entire desk is an ESD workstation)

Open the side panel with the two press in latches at the back and swing it open from the back edge.

Side panel removed

Now unplug the 50 pin SCSI ribbon cable from the board (It has two levers on each end that pivot out and backwards that will assist you with this task. Try and move them out at the same time), unplug the power lead to the motherboard (There is a clip that needs to be pressed in at the top to release it), the drive power leads (These also have a clip like the power lead to the motherboard) and the floppy drive ribbon cable. (Despite the difference in size, it comes out just like the SCSI cable).
Fold the cables up and out the way. Don’t worry about this with the motherboard power cable.

Now, on the top metal rails between the drives and the power supply, remove the outer two visible screws. There is a concealed screw behind the front fascia, but we’ll get to it shortly.

Cables folded back and outer screws removed.

Now slide the entire upper drive assembly towards the back of the case. There’s a little thumbrest near the back that can assist. Remove the drive assembly and put aside.

Next you need to remove the front fascia. First, unplug the speaker. It simply unclips from the two pins it’s connected to. There are two plastic clips in the middle of the fascia that protrude into the case. There are another two underneath the system.

Carefully lever the clips away so that you can remove the fascia. Just be aware, these plastics are up to 30 years old, and can be quite brittle. Take it gently!

Fascia removed.

Once the fascia is gone, there are three screws (Two at the back and one at the front) to remove to allow the power supply to come out. Once they have been removed, the power supply can be lifted straight up and out by the cable ties through it.

One at the front, two at the back.

With the power supply out the way, you can now reach the VRAM slots. they’re the 4 white ones at the top.

Starting with the uppermost SIMM socket, place the VRAM SIMMs in with the chips facing the top of the board (assuming 256K SIMMs. For 512K simms, put the side marked “256K” facing the top) in at about a 45 degree angle, and slowly, applying a pressure towards the point the SIMM meets the socket, lever the SIMM to vertical, making sure both metal clips engage.

Once all four are populated, you can start buttoning the whole system back together. It’s pretty much a reverse of disassembly. The only trick I can suggest is that while inserting the power supply, it’s easiest to get the front guide in the “L” shaped guide before getting the back part lined up. Don’t forget to plug back in the speaker.

Power on and you now can use 24 bit colour in all but the highest resolutions. Those now support thousands (16 bit) of colours. Enjoy your new Macintosh setup.

Some upgrades for the Quadra 950

Thanks to the ever generous Greg, I have received several NuBus cards to my Macintosh Quadra 950. They’re provided in a “unknown” state, so it’s going to be a fun job to install some of these and see what we can get working…

So what do we have here?


First up we have a generous helping of VRAM for the 950. This will bring my screen resolution and colour depth to maximum on the built in video.

Next up we have a pair of network cards. Both have 10_T connectors, which is good. This will allow me to get the 950 on the house network.

Next up we have a Lapis PROCOLORSERVER 8 II. Yep, bit of a mouthful. It’s a video card. There are drivers available for it. It is fully populated with RAM. So far I have not been able to find much more about it. Mysteeerious! I’m hoping it will feature some QuickTime acceleration on those two FPGAs.

Next up is a RasterOps accelerator. These things act as a cache. You stick RAM in the 30 pin SIMM sockets on the end and it can accelerate performance. No idea if it’ll make much of a difference. I’ll need to benchmark beforehand and afterwards.

Here’s a pretty standard RADIUS Pivot card. (A V2.6) This is a backup card “just in case”. RADIUS cards are well supported.

Finally the DigiDesign AUDIOMEDIA. This appears to be quite a competent sound card. Check out the white Motorola 56001 DSP chip! Hope I can get that working 🙂

I plan to install these upgrades one-by-one over several days. This way I’ll be able to test the cards without having to work out what is breaking things.