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.

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 Sordan.ie 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?

VRAM

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.

The Archimedes is back on the bench

Now I have an oscilloscope, I thought it was time to break out the Archimedes. So far it has resisted my attempts to diagnose exactly what is wrong with it but I will persevere.

Why must you vex me so?

Symptoms are the same whether I use a Gotek or a real drive.
When you try and access the drive you get a “Drive empty” error. The disk drive motor does not spin.

I have:
Replaced the drive cable, making sure I use one with pin 1 cut for the Goteks. (It doesn’t make life easier with the pin order being reversed on the A440)
Tried two different Goteks (They power up and respond. I have rebuilt the config to have the right settings for the Archimedes as well)
Checked voltages (5v and 12v are fine at the cable)
Replaced a mess of logic in and around the FDD controller. ICs 29,30,38,46.
Traced all the connections from the 34 pin FDD connector to the next chip / resistor array.
Reset the Config. (Hold down Delete when booting the Archimedes. You also need to do this if the CMOS battery ever gets disconnected)
Replaced the WD1772 with another one from ExxosUK (Who is probably as close to a reliable source as I could find)

I’m hitting a strange issue when I connect my ‘scope to the system and try measuring the drive signals, where rather than reading, then throwing an error, the system just locks up instead. I need to learn more about using my oscilloscope.

Meanwhile I have done a couple of other projects.

I got offered, and accepted a huge CRT TV. This thing took three of us to lift it. It’s a “29 inch” model and is obviously a late model system, with both SVideo and Component inputs. Unfortunately on inspection, I noticed a very bulgy capacitor, so that’s staying off until I can replace it.

It was very dusty inside too.
Bulgy cap is bulgy.

I finally got around to making a Apple IIgs to SCART adapter cable so I could use my IIgs with my Commodore 1081 monitor. It’s pretty simple. 2 resistors and everything else is just connect the pin to the connector. Here is the guide I used. The SCART connector I got from a cable I had surplus. I’d purchased an RGB cable for my Sega Megadrive II, but despite me choosing the right item on the order, I was shipped a cable for the Megadrive 1. Thankfully they let me keep the incorrect cable and shipped me the right replacement. I kept the incorrect cable around “just in case” and just desoldered the cable and used the connector when I went to make this new cable.

The CRT turns the harsh lines into softer blurs, and what looked like odd dark blue and white bars on LCD came through as a light blue shade on the CRT.

On an LCD, that background is harsh stripes.

As is often the case, the cable flopped around loose in the 15 pin shell. 3D printer to the rescue! I have even redesigned the OpenSCAD file I sue to generate these cable glands to be parametrised, so I can easily update it to match new cable hoods and cable thicknesses as needed. If there’s any interest I can stick it up on GitHub, but it’s a really simple design.

This took 2 minutes an 40 seconds to run. Most systems can do it in well under a minute.

Finally I got the piece I needed to fix my Creativision keyboard adapter, and got it working. This allowed me to type in a piece of software developed by Noel’s Retro Lab, used to benchmark BASIC on 8 bit systems. We managed to turn in a truly abysmal speed, making the BASIC on the Creativision among the slowest so far, and slower than even notoriously slow systems like the ZX81. Our shame is also our pride.

I’ve also done some maintenance, in the form of swapping out the regulators, and an old capacitor. I am still seeing some issues with it so I need to get to the bottom of that. I need to heatsink the graphics processor in it next, as they are notorious for running excessively hot.

Posting will slow for a while

So I’ve gone back to work after an extended holiday, so output is likely to slow for a bit.

However, I’m still doing retro “stuff” so I thought I’d share some of it.

One of the coolest projects I completed on the weekend was building an MT32Pi Hat. This consists of a Raspberry Pi running a “Bare Metal” emulator to run emulation of both the Roland MT-32 (Thus the name) and a SoundFont compatible synthesiser. The MT-32 was a very popular early MIDI module, with a lot of support on a huge range of platforms, from MS DOS systems, Atari ST, Amiga and even Apple II.

So far it’s been fun playing with it. I only have the single computer capable of playing MIDI files currently but that has kept me amused. I’m working on getting MIDI out working on others.

Why yes, that IS held in to the bog standard Pi Case with Electrical tape. Why do you ask?

I’ve also been doing more work on the case for the Microbee. I need to do at least one more MDF prototype before I go for the “main” Acrylic cut, but she’s getting there!

The older prototype case is at the back.

I have also started cutting MDF for the Amiga case I have been planning for at least 4 years. This is being slowed down by a general shortage of MDF available right now.

I call this “using all of the buffalo”.

I have printed a backplate for my Dick Smith Wizzard, from a design from Mr Lurch.

I think the pitting comes from not letting the resin settle before printing.

Finally, an interesting box arrived today. Oooh! What could it be?

Expanding on removing corrosion caused by batteries.

Recently in a Facebook chat, the question was asked: “How do I deal with battery acid damage so things don’t get worse?”.

Having recently dealt with both the Quadra 950 and the Amiga 2000, I felt eminently qualified. Here is my answer

This is my method. There are many like it but this is mine.
Remove the motherboard, rinse the affected area with white vinegar. It should “fizz”. Keep applying vinegar until the fizzing stops.
Rinse thoroughly with tap water and scrub the area. Rinse with distilled water. Rinse with isopropyl alcohol. (You need to get under the chips).
Place in a hot, dry environment. (I stick it in the sun for an hour or so) This’ll neutralise that alkaline from the battery completely.
You may need to scrub at tracks if the corrosion has got under the solder mask (Tracks will look “dirty” under the mask). If so, you need to remove the mask and clean the track with a very mild abrasive (ink eraser or fiberglass pen) until the corrosion is gone.
You’ll then need to seal the tracks. There are professional products out there, but I’m slack so I use nailpolish.

Now, while this is a good answer and barely fitted in a standard reply, I thought I’d expand on it a bit here.

Remove the motherboard, rinse the affected area with white vinegar. It should “fizz”. Keep applying vinegar until the fizzing stops.

To expand on this, I’d be using an old toothbrush to apply the vinegar, and scrubbing aggressively. Not “lift tracks” aggressively, but like you’re brushing your teeth. You really want to react as much of that alkaline as you can.

Rinse thoroughly with tap water and scrub the area. Rinse with distilled water. Rinse with isopropyl alcohol. (You need to get under the chips).

Each time you want to make sure you treat all the are of the previous step. With the tap water step, you really want to remove every last bit of alkaline, vinegar and any other by-products of the reactions, if possible. Distilled water can be a single pass. With the isopropanol, you’re trying to get rid of water trapped under things like chips and sockets. When I used to do this for a living, we had a big tin of it, and we’d soak the entire motherboard in the isopropyl for 15-30 minutes before drying.

Place in a hot, dry environment. (I stick it in the sun for an hour or so) This’ll neutralise that alkaline from the battery completely.

This is further drying. If it’s not sunny, once most of the iso is gone, you can stick it in an oven set to about 50°C for 15 to 20 minutes. That should dry it out.

You may need to scrub at tracks if the corrosion has got under the solder mask (Tracks will look “dirty” under the mask). If so, you need to remove the mask and clean the track with a very mild abrasive (ink eraser or fiberglass pen) until the corrosion is gone.

You can also scrape back the mask carefully with a fine flat bladed screwdriver. Also watch out for fibreglass pens. They drop itchy, irritating fibres everywhere. I always work over a piece of paper, which I fold and discard at the end.

You’ll then need to seal the tracks. There are professional products out there, but I’m slack so I use nailpolish.

Yep. Nail polish. A colour so hideous my wife, who collects nail polishes, didn’t want. Works well, and at least I know where I’ve covered tracks.

Understanding Memory Chip Codes

I wrote this up for a forum post and thought I’d share it here. It’s not 100% accurate but is “good enough” to help in a lot of cases.

The discussion started with a poster trying to understand how we knew what the capacity of a 41256 RAM chip was.

It’s actually there in the chip name. There’s a standard (Gotta love standards. There’s so many to pick from)

The first digit is whether it’s SRAM or DRAM. 4 for DRAM, 6 for SRAM, so this is a DRAM chip.

The second digit is how many “bits wide” the chip is. Ie how many data pins are there exposed. Commonly it’ll be 1 or 4. I suspect there’s 8 but I’ve never seen it. So  41 series is 1 bit wide DRAM. You can only read / write 1 pit per chip. I have systems using 44 series RAM (Commodore 64 later models) so they’re 4 bits wide and you can read or write a 4 bit nibble per chip.

The rest of the numbers to the hyphen is the number of “cells” of memory there is. Now this is tricky, because you need to multiply the number of “bits wide” the RAM is by this number to get the actual bits, and then by 1024, because it’s a measurement of kilocells. (Confused yet? Took me YEARS to be able to read these). So this chip is 256k x 1 bit wide, thus 32 kilobytes of potential storage.

Now remember that second digit? This is where that becomes significant.

The RAM on late model C64s was 4464 RAM. Thus DRAM, 4 bits wide, 64k cells of 4 bits wide. Thus each of these was also 32 kilobyes wide. The difference? Whereas 41256 needs eight chips to make an 8 bit datapath, 4464 only needed 2 chips to to make the full 8 bit datapath.

Now, not all systems have 8 bit datapaths. I have an Archimedes (Sadly, currently not working as well as it should) that has a 32 bit wide data bus.  It has an absolute sea of 411024 RAM on the motherboard (The nomenclature is slightly different because it was sourced by a different manufacturer, but it’s equivelent). 

So, DRAM, 1 bit wide, 1megabit.  But it needs to read it 32 bits at a time, so there are 32 of them, for a grand total of 4MB of RAM.