Updates and some Smaller Projects

Well I haven’t stopped working on projects and while some of the have been successful, others have not been so successful. It doesn’t help that my desoldering station has broken. I just need to get some specialised glue to fix it.

Archimedes

The Archie still has a bunged Floppy Disk Drive and I’m stumped as to what the problem could be. I’ve traced every wire from the FDD to the the chips they connect to. I have then checked from those chips to either the bus or to the next chip. I have also checked those chips. I’ve run out of ideas as to what to look at next. Back in the naughty corner with it for now. It’s a pity. I’d love to have it working well enough that I could use it. I even have upgrades for it that are just sitting around as I can’t use them.

Testing all the connections. They all passed.

Commodore 64

I have a C64 that’s dead. Black screen. The Dead Test cart flashes once. That usually indicates the first bank of RAM. I’ve swapped that RAM with known good RAM. No change. I’ve swapped the PLA. No change. I probably need to get it under an Oscilloscope. This brings me to my next point.

Essential for debugging Commodore 64s

BitScope Oscilloscope.

I’ve hit the limits of what I can do with this scope. The big limitation is the lack of documentation. The website links only to a defunct video. Not the most helpful. I think I’ll need to get a new ‘scope.

Amiga MultiKick

I tried upgrading the ROM set on my 4 ROM Amiga MultiKick. I’m using an adapter in my TL866II+ to allow me to burn larger ROMs, in sections. It works well, but I haven’t been able to get Kickstart 2 to work. Normally it would just be a matter of reversing the byte order and burning it out. It shows up in the TL866 and looks sane. I just get the screen flashing red. The other 3 ROMs work fine. I even went out to see if there was a different version of the ROM and there’s not. I’m even using the official ROM from Cloanto that came with Amiga Forever when I purchased it.

This came with Kickstart 1.3, 3.1, 3.2 and DiagROM. I don’t need 3.2 on this system, and I don’t have a license for it. I’m trying to get Kickstart 2.05.

1081 CRT Monitor

This came with the Amiga 2000 and was reported as having a dead Monitor switch. Thankfully replacements are available and I even had some in stock. It was a relatively pain free job to crack the cover, remove the switch and solder on a new switch in it’s place. I even added shrinkwrap where the original switch had none. Tested OK with my Amiga. This is my first monitor with SCART.

I’d forgotten how heavy CRTs were.

GBS Control

I’d started this project a long time ago, but finally got it working the way I wanted. Effectively it’s a hack of the GBS8200 arcade scaler to make it more compatible and more stable with a wide range of systems. It consists of the GBS 8200, with an ESP32 development board wired in, as well as an optional high accuracy chip clock generator.
The whole thing is silly cheap to build and the picture quality is astounding. I’m using mine as a flicker fixer for my Amigas.
One of the more interesting things I attempted this time around was to add shielding to unshielded cables. The wires used for the video signal were just straight hookup wire, terminated in the “special” connector for the GBS. I found some old coax, stripped the outer plastic sheath carefully, then removed the copper inner sheath. I then “puffed” this up by compressing it along the direction the sheath ran. I ran the cables I wanted to shield through the middle of the copper sheath then stretched the sheath out over the wires. I terminated both ends with glue impregnated heatshrink to make sure it doesn’t go anywhere.
I don’t know if it’ll actually make a difference, but it sure looks nice.

Left: GBS Control. Right: NecroWare MCE Adapter

NecroWare MCE Adapter

This is a little kit I got made up when I ordered the boards for the Omega MSX. It’s designed to convert TTL level signals like those from an IBM CGA adapter over to VGA style signalling. It’s based around a GAL to do the level shifting. In fact, this was the first GAL I ever programmed! (I programmed an additional 3 for the Omega MSX).
While not advertised as working with the Commodore 128, I thought it was worthwhile to at least attempt to use it with the C128, as I knew the signalling was supposedly the same.
I’m pleased to confirm it worked flawlessly.
I have another Necroware project just pending parts.

Amiga 2000

I’ve started the long, long path of trying to get the Amiga 2000 back on its feet. Step one is getting the power supply sorted. This is proving “exciting” as the existing power supply was not only dead in an exceedingly difficult to fix way, the power supply itself had been mercilessly hacked by a previous owner.
My current plan is to modify an ATX Power supply to work in its place. I’ve modified the old PSU frame to take the new PSU. I just need to wire the Amiga loom to the ATX PSU. I’d like to do it in a way that I can swap out the PSU if needed. I plan to start by attacking an old motherboard for its ATX connector. I’ll need a desoldering station for that.

Someone took to it with tin snips. They just bent over the metal rather than removing it. I’ve bent it straight since.
This blown cap is under a heatsink. In turn power transistors are clamped to it. Their access screws can’t be accessed without desoldering several other components. I gave up.
ATX PSU in the chassis of the dead PSU.

Building a computer (Omega MSX)

One thing I’ve wanted to do for a very long time is to build a kit computer. Originally I planned to build a Spectrum 128k clone. I’ll probably still do that in the future, but as I had a Spectrum already, there was less pressure to get another speccy. I kept pushing it back.

Then I saw the Omega MSX.

The Omega is an MSX 2 “remake” with some compatibility with the MSX 2+ standard. It’s an open source project and the boards can be ordered from any PCB fab of your choice. I ordered some boards last year, as well as a big order from an e-bay seller who was selling “all the silicon” components as a bundle. I ordered the special 64 pin oddly spaced socket for the video chip from AliExpress. Just before Christmas I ordered the rest of the components from two different suppliers. This was mostly passives, connectors and sockets. Incidentally, if any suppliers want to sponsor me, reach out to me!

The board with the first few resistors in.
Some of the resistor arrays had these strange long legs. Presumably for automated assembly. I used them to repair a broken chip later.
All the resistor and resistor arrays are now in.
Sockets, resistors and all the non polarised capacitors.
Everything is now in. I just need to install the chips in the sockets.

Once I had all the components, (Bar three. More on that later) it was time to star assembling. This was remarkably simple. I simply worked from lowest to highest, starting with the diodes, then resistors, then resistor arrays, sockets, capacitors and finally connectors. I only had a few mishaps along the way.

  • Firstly, one of the DRAM did not want to go in to the socket and I accidently snapped off one of the legs. A quick patch with a bit cut off one of the resistor arrays and it dropped right in.
  • Secondly, I bent a pin on the Yamaha sound chip. I didn’t even notice this until final inspection. Simply bending it out was enough to fix the issue.
  • Thirdly, and this only came up in testing, I had the SRAM and EPROM switched. Neither was the exact brand as specified in the BOM. They were substitutions, so this is my own damned fault. Swapping the two chips fixed this final main board issue.

I was testing and inspecting continuously as I assembled things. Mostly I was just making sure there were no shorts between 5v and GND. I checked after the resistors and sockets went in, and then again after the capacitors went in, and again, once more, once the chips were in. At no point did I get a short, so that made me confident enough to actually try the system.

On my first power up, with I got a black screen. This was good! This meant that enough signal was being generated that my screen was synching to a valid video signal. This usually means that most of the system is executing. Occasionally on startup, I’d also get a few seconds of garbage on screen. More signs that it was mostly working. After some hair tearing, I finally caught on to the issue with the SRAM and EPROM being swapped. Swapping them back and we had success! The MSX logo came up and it booted to a command prompt.

Keyboard, pre stabilisers.
MSX Basic!

At this point, the second round of issues came up, and they were all with the keyboard.

  • Firstly, I’d accidently ordered the wrong resistor array for the keyboard. Initially I just bodged in a set of the appropriate resistors and made my own array. However, while doing some cleaning of a storage container full of components, I later discovered that I did have the correct array. Ironically, it was a part I’d incorrectly ordered for a completely different project. Hang on to your spare parts, folks. You never know when they’ll be useful.
  • Secondly the LEDs were super dim. Guess what? A 470kΩ resistor is not the same as a 470Ω resistor. I’d used resistors with a thousand times the resistance. No wonder the resistors were dim! A quick substitution and we were good to go.
  • Finally I’d got some of the LEDs in backwards. In my defense, the boards were marked poorly for polarity on these components.
Heat sinks in place.

I will mention some of my experience building this board:

  • There are a lot of capacitors! Over 90. I think I went a bit cross-eyed installing them. Finding where they all went was time consuming. There were two I couldn’t find after several minutes of searching. In the end, I opened the PCB in KiCAD and used the built in search function to find where they were supposed to go.
  • Ditto for 74 series “jellybean” logic. I ended up having to use KiCAD for finding one of the locations.
  • There were three components that I simply could not locate. I have them on back order. Thankfully they are only the audio out RCA socket, the RTC battery holder and the printer port connector, none of which will slow me down.
  • The instructions are more than sparse. They’re practically hiding. I hit several issues where I had to guess. Of course, after the build, I found the following site which has excellent instructions. They’re in Spanish. Use an auto translator. You’ll be fine.
  • I haven’t been able to get RGB video working yet. I still have a little more work to try before I give up. SVideo is awesome, though.
  • Compiling the BIOS seems completely undocumented. I just grabbed a “pre rolled” BIOS instead.
  • The JED files for the GALs were difficult to find. They’re on the GitHub page. They’re just not obvious. All the instructions talk about using a converter to convert a text file to a JED. Unfortunately the software doesn’t work under 64 bit Windows. Just look for the JEDs.
  • The keyboard assembly for the spacebar is horrible. You have to bend your own stabiliser bar. Mine is still not right. It works but it’s just not “right”.
  • There’s this one Sony chip with a strange width. I ended up using two pieces of machined pin strip socket.
  • The stabilisers for the keyboard vexed me for a long time. Firstly, you need to slide the smaller part into the larger part. Then you clip the stabiliser bar into a pair of the stabilisers. It goes in the middle hole. It clips in at the edge. The stabilisers then clip in. You put the smaller side with the lip into the larger hole and the side with the split goes into the smaller hole.
  • The LEDs on the keys go through the keys. Don’t get this wrong.
Through the hole.Don’t try soldering them down first.
The completed assembly. I stole these keys off another keyboard. I want better keys.

Big Boi Mac

TLDR: I have a working Quadra 950

The Long Version: So on December 31, I went and picked up two Quadra 950s, in an unknown state, but one with battery damage.

Having taken the first off as a break (Being repeatedly woken by the neighbours, who decided to “party all night” does not help one’s ability to fix systems. I finally asked them to turn the music off at 5:15am, having already asked them to turn it down at 4am) I got stuck into the corroded system on the Saturday.

Pulling open the system revealed a long, still slightly sticky trail of rust and corrosion, running between two sets of SIMM sockets.

Eww!

It took me a few goes to get the system apart. The procedure (Which I have now done several times now) is as follows:

  1. Remove the front cover over the speaker. It’s held on with two clips on the bottom of the panel, and two near the top, which clip through the case and are accessed from the inside of the case. Unclip the speaker wire.
  2. Remove the drives and drive caddies. Don’t forget to remove power cables and both the floppy drive cable and the SCSI cable. The caddies are held in by a single screw on the front of each caddy. The are clipped in and slide straight out towards you. Be careful around the floppy drive. You may have to unclip one side of it’s front panel.
  3. Remove the caddy holder. It’s held in with two screws. It slides sideways towards the back of the case and then it slides forward.
  4. Remove the power supply. First, unclip the main board power connector. It’s held in with a small press clip. Then remove three screws. One at the front and two at the back. It slides out towards you.
  5. Remove the programmer and reset buttons. Gently squeeze them from inside the case just before they enter the front panel, then push them forward out of the front of the case.
  6. On the back of the case, on the right hand side, in line with the gap between the SIMM sockets is a spring loaded plastic clip. Push down on it and slide the whole motherboard sideways towards the front of the case. The whole motherboard will now be loose. Pick it up from the front side of the case and lift it out. The back half will follow.
POP! Dribble dribble dribble.

Once I had it out, I took it across to the sink and rinsed and scrubbed it to get the worst of the nastiness off it. I followed with plenty of vinegar. (I left it for a few seconds until the bubbling stopped). Another rinse under the tap followed by distilled water followed by a spray of Isopropyl alcohol over all the major chips.

I made sure I scrubbed the back too as some of the corrosion seemed to have worked its way down the legs of the SIMM sockets and out the other side. This worries me as it may mean the board has corrosion on one of the middle layers.

After that, out into the sun to bake off all the water. It was a nice hot day so the water evaporated easily. I flipped the board to make sure no water was hiding under anything and gave it a second spray of Iso.

While it was drying I checked out the SIMMs that had been in the system.

There were 12 SIMMs. Two were a complete write off. Two, however, seemed worth salvaging as they were labelled “8MB” so back into the whole water -> vinegar -> water -> distilled water -> isopropyl. The rest were completely fine. I have them a quick cleanup anyway and all out in the sun.

Drying in the Aussie sun. Yes, that’s a BBQ they’re sitting on.

Now onto the case. Same process as before then out in the sun. It’s pretty badly stained, but it’s inside the case so, what can you do?

Snot inside the case

I let that all sit and dry and started working on a Mac to VGA adapter. There are some articles out there that list all sorts of details, but the best guide I found was this one. I built myself a nice high bandwidth connector. Not pretty but who cares?

Not pretty, but my kind of not pretty.

Not wanting to work more on the systems, but not wanting to lose momentum, I also start looking at the floppy drive, which needs a whole lotta love. I start work on it but at this point I chose to stop for the night.

The next day I was feeling more enthused. I asked around on the “Vintage Apple and Macintosh Enthusiasts of Australia” Facebook group if there was anything I’d need to check before firing up the “good” system.

I also went and watched an excellent video on cleaning and servicing the floppy drive, while I waited for replies to my query on Facebook. I immediately got to work and cleaned and lubricated the drive.

I went back to check on Facebook, and after several cries of “Naah just turn it on” (Including one from a certain expert) I decided to plug it in and turn it on.

Nothing.

Hmm. Maybe the power supply? I have a spare. Swapped it over.

Nothing.

At this point I measured some resistances and the whole board seemed to be short circuited, showing only 5Ω of resistance across the 5V rail. Odd. That didn’t sound right. Out came the multimeter and I spent the next half hour checking resistance across all the Tantalum capacitors.

It all looked fine.

I even started looking if there were tricks to turning on the PSU by “hotwiring” it in a similar fashion to what you can do with ATX power supplies. It was about this point I made an important discovery. What I assumed were power buttons on the front? They’re the programmer’s button and the reset button. You need to plug in a keyboard and turn it on from there. D’oh!

Plug in the keyboard (and mouse for good measure) and press the button!
Immediately the enormous fan spins up… and spins back down. This is actually good! It’s doing “something”. A kind soul on the forums mentions that this is probably a bad PSU. Oh well. I do have TWO of them. Plug in the second drive and… whoosh! It roars to life.

I have the video plugged in and I wait and wait and wait, and just when I’m about to give up hope, up comes a hashed grey screen and a cursor. We have life! There’s the familiar “Insert floppy” symbol.

Alright!

I happen to have a floppy disk on hand so let’s check the floppy drive. The disk drops in fine, attempts to read, fails (As expected) and then ejects… Or tries to eject.

The eject mechanism made a sad little whine, then a grinding noise followed by a whirring noise. Welp. Time to look at replacing that gear that always fails. Sure enough it has turned to orange powder. It’s amazing! The gear literally is softer than chalk.

I turn the drive gear so the notch is to the front. This will trip the sensor so the drive stops spinning. I also reached out to my friend who is a much better 3D Printer person than me, to see if she can print me a replacement gear or two on her high end resin printers.

OK so we are now at the point where we can start building up the server some more. I have several SCSI hard disks and some SCSI CD ROM drives. I start “simple” by testing the three drives that came with the Quadras. The first disk I try doesn’t even try and spin up. The second makes a disturbing “pew pew!” noise and the third spins up but does nothing.

Time for some lateral thinking. I know it’s not termination. Could it simply be that the drive is unpartitioned? OK so if we start from that, how do we get the system installed? What about booting from CD? I wanted to put one in there anyway…

Out comes the CD ROM. I quickly find a copy of System 7.5.3 and burn it to a blank CD/ I check the jumpers are all “sane”, plug it in and hold down the ‘C’ key to tell the system to boot from the drive. Amazingly, it boots first time.

Happy Mac!

Yahoo! We have a working Macintosh! Best of all, the SCSI hard disk that’s in there is recognised. I do a complete install, and it even boots correctly. I am amazed.

Happy Drive

Just in case I check the other two drives and with either of them in, the system won’t boot. I think the drives themselves are completely dead. A pity, but 350MB should keep me going for now. Down the track I might buy a different storage solution, or work on some of my random SCSI CDs I have lying around the place.

At this point I check and I have 40MB of RAM already in this system. Short of the maximum 256GB, but not to be sneezed at. Wonder if I can do better? Remember those 8MB sticks? I pull them out, clean them up with an eraser, then reflow the contacts with fresh solder as the current surface is so bad it’s brown down to the copper.

Taking the outermost bank of SIMMs out and rebooting, my memory drops down to 36MB. Good. I figured this one has 2 banks of 4 x 4MB sticks for a total of 32MB and 2 banks of 4 x 1MB for a total of 8MB.

By removing the final bank or 4 x 1MB and substituting 4 x 8Mb I can theoretically bring it all the way up to 68MB. Let’s see if my Plan works?

So much RAM!

It works! I’ve salvaged the 8MB SIMMs.

At this point I start doing cosmetic stuff. The first thing I notice is that somewhere along the line, the system has taken an awful knock and both the case and PSU are actually bent. The case I’m using is also stained with something nasty that doesn’t want to come off the outside of the case.

The PSU I eventually fixed (After an abortive attempt to swap the shell with that of the PSU with dead capacitors) with some good old percussive maintenance. I hit it with a hammer over a block of wood until it’s back in shape. Now it fits nicely.

As for the case, I ended up swapping everything over to the other case, as it’s in a much better state. A bit of elbow grease and it looks quite presentable. As a side effect I discovered the speaker in the “dirty” case is dead.

(For those trying to keep up, there were two Quadras, one was clean in good shape but with a corroded motherboard, 2 dead HDDs and a dead PSU. The other Quadra had a bent case, a damaged speaker but a good motherboard and a working but bent power supply.)

This thing is a monster!

There is still a lot of work to do. For reasons I am currently unsure of, the CD ROM seems to have stopped. Not sure if it’s the drive or the system. (I’ve tried a second SCSI CD ROM but I don’t know if that one is good or not either. I’ll have to try my external case and see if the drive works with the SE/30). I also need to make a cover for the front of the system to cover the 5¼” drive bay but still allow access to the CD ROM.

There also may be some upgrades in the future. More on those as they come to hand.

I also want to start work on the second system. If I can, I’d like to salvage at least some of that system. Hopefully I can fix the mainboard and the PSU. It would be great to salvage another system.

Rounding Out 2021

What a year!

To cap it off nicely I was visiting a fellow collector today. (Hi Greg!) I wanted to drop him off some Commodore 64 stuff for his collection and he had a nice surprise for me!

Not one, but two Mac Quadra 950s. Pretty much the “top” 68K Macintoshes available!

Wow!

Banana to scale

These are truly massive full tower systems, so once I have on on it’s feet, it’ll be living under the desk, not on the shelf.

One, unfortunately, has battery damage, so tomorrow I’ll be neutralising that with the same Vinegar -> Distilled Water -> Isopropanol treatment that I did to the Amiga 2000.

I’m extremely hopeful I’ll be able to get one good one out of the pair.

†The 840av has a slightly faster 68040 in it but only can take half as much RAM. It is also not as expandable.

EDIT: I just realised I got fourteen new computers in 2021. So much for “no new systems” 😀
That’s more than half my collection arrived this year. Amazing! So much generosity from so many people!

The final MicroBee is complete!

Thanks to uBee and Brad, I now have all the parts to finish off my 16k MicroBee.

It’s a beauty! Yes, it’s yellowed. Yes, there’s engravings in the top cover. Yes, the keys look like the teeth of a chain smoker, but that is exactly the type of character I like in my systems.

Some quick notes:

The screws holding the top case to the lower case turn out to be an exact match for a bunch I purchased in bulk from Jaycar a few years back. I think they were the part number HP0414, but I’ll check and post here later.

The “case badge” was designed up in CorelDraw and printed onto silver paper. I covered it with clear contact, cut it with a roller cutter for straight edges and then applied some workable fixative spray glue. This kind of pipeline (CorelDraw, Laser printer, Roller Cutter, Workable Fixative) has become my “go to” to make surprisingly realistic badges and labels for a whole heap of systems. They’ll never pass anything more than a passing inspection, but they do look better than nothing at all.

Go. Go. Go. Gotek!

In my last big order from a ubiquitous Chinese e-commerce site, I ordered FIVE Gotek drives, earmarked for a variety of systems, including my Amiga 1200 (when it gets built), my Amiga 600 and the Atari STᴱ.

OMG GOTEK! (And OLED and Rotary Encoder)

I had a cunning plan, and one of the reasons I’ve been so quiet recently was that I’ve been working on the plan.

You see, one of the things I don’t like with the Gotek is, by default, it has only got a 3×7 segment display, and a pair of buttons to run things. I wanted upgrades in the form of a nice big OLED display and a rotary dial. But where to put them? When I’d been working on the Archimedes, I’d had the clever idea to mount the screen on a cable, and that seemed to work well. I wanted to take that to the next level, so I’d been thinking about the design for a while.

The old version. It worked…

The long linear connector of the design for the Archimedes took up space and was not very elegant. A better design was needed. I knew I only needed 7 wires.

“Seven you say? Surely the rotary encoder needs 5 and the OLED needs 4. Isn’t that nine?”
Aha! you’ve been fooled! The GND and +3.3V pins are shared between the Rotary encoder and the OLED, and the Rotary encoder actually only needs 4 pins not 5.

I decided on using a DuPont connector for the computers and Pin Header for the OLED Display. I settled on a pin being removed to make sure the connector couldn’t be plugged in backwards and from there a 2×4 row of pins was the logical size.

I sat down with the Wiki and carefully plotted out my pins. Then I looked at them again and rearranged the pins completely to be more logical 😀

Trust me! These are all you need!

Grabbing out the crimper I made up the socket in about 40 minutes. Note to self, next time use multicoloured “rainbow” wires. They’re a lot easier to keep track of what pin goes where.

It took me 3 goes to get all the pins in the right place.

At this point I made the other half. This consisted, on the connector side, of some experimenter’s board, some pin header and a zip tie for strain relief. I soldered on some nice flexible 8 core cable and soldered on the OLED and rotary encoder to the other end.

At this point I tested everything and it worked as planned.

I’d already flashed the Goteks with FlashFloppy, but I needed to get some more pin header, with 2 rows and a right angle, as if the pins stick straight up, you can’t close the case. A quick trip to Altronics fixed that. Now the connectors could lie flat inside the case.

Next I 3D printed two different styles of bracket (one for the Amiga 600 and one for the STᴱ to hold the DuPont connectors in place. A dab of super glue and the whole things were done on the computer side.

Atari STe with the connector in the LCD slot.
FF for Flash Floppy modified. The thing on the top is a pizeo speaker for the drive click.

Next up I printed up a nice case for the OLED and the Rotary dial. It’s almost good enough for release. I need to tweak some dimensions but it still looks good.

I’m happy with the 3D printer.

Finally, having accidentally shorted two wires and severed a third, I resoldered the connector, covered it in hot glue, then a piece of cloth that I’d impregnated with hot glue, then finally gently heated the whole thing so everything hot glue bonded together. THis gives me an incredibly strong connector I can easily remove.

Surprisingly practical.

I’m very happy with this!

Works on Amigas too!

Upgrades, Problems, Parts

It’s been an exciting few weeks.

Archimedes

The Archimedes continues to confound me. I finally got a replacement 1772, plugged it in and… No change!
At this point I have swapped out all the chips that feed the floppy disk. If you look at the schematics, I have socketed and tested IC29, IC30, IC38, IC 46, IC47 and RP1. No change. It’s going to be continuity testing from here on out, which won’t be fun.

I have replaced many of these,

Upgrades

Some of the upgrades I recently ordered started flowing in at last as well.

I got an ElkSD128, which brings the Acorn Electron up to an insane 140k of RAM and also adds both a Joystick adapter AND a SD card interface. This makes the Electron a little powerhouse!.

An unassuming white box.
How much RAM?
Press “T”! Press “T”!

I got a TFW8B SD2PET Future which finally adds easy to use storage to my Commodore PET. Files at last! (I promptly loaded a few games to muddle around with. I do like how well documented this was.)

Plugged in
DOS Wedge loaded and now I can see all the software on the SD
Like PETfrog

I also got a set of five Gotek FDD emulators which I have converted to FlashFloppy firmware. So far I’ve only installed one in my Amiga 600, with a nifty external rotary encoder and OLED. (I also have some 3D bits and pieces to make it up into a nice little package. I’ll be covering all the Gotek stuff in a separate post in the next few weeks.)

Many machines will no longer need Floppy disks

Spectrum

Finally, I got a DIVMMC Enjoy Pro. Unfortunately this isn’t working. The DIVMMC isn’t displaying its proper BIOS screen.
Next step was to clean the edge connector, but that didn’t help. (I also reflowed the power connector because I was seeing some unreliability.)
As this still didn’t help, and the next step involved getting a new Z80, I decided to completely resolve the edge connector as being a potential issue. The Spectrum doesn’t have fancy gold plated edge connectors. It has a simple solder plated edge connector. This was looking a bit “well loved” so I took the time to flow and clean each and every edge connector “pin” on the edge connector. My methodology was pretty simple. I dropped some fresh flux across the pin, then ran fresh solder onto the pin, using the hot soldering iron tip to “scrub” the underlying corrosion patches to remove them, finally following up with solder braid to bring them back to a smooth “factory finish”.

The left side has had fresh solder applied. The right has fresh flux. the “marks” in each pin are corrosion into the solder.
Here they are after the solder has been cleaned up with solder braid.


Alas the problems persisted. I was a bit depressed by this and was concerned I’d need to buy a new Z80 just to test. Then I remembered I actually had a spare Z80 in my collection.
Out came the desoldering gun, and with a little effort I was able to desolder the z80, drop in a new socket and test.

New socket under the Z80 CPU. It’s the long chip to the right under the heatsink.

Unfortunately the system still failed to load the DIVMMC BIOS. I’ve reached out to ByteDelight for more diagnostics hints. Hopefully it won’t need to go back to them. It’d be almost be cheaper for them to send me a new one.

Microbee

I caught up with Brad from the MSPP forums for a coffee (Hi Brad!) and we chatted for a good solid hour and twenty minutes. Brad had very kindly donated me the missing key for the 16K Microbee. It’s keyboard is complete!
I have a potential top and keyboard cover coming, which would nicely finish this system.

I have taken CTRL

I’ve also started work on an evil project to build an adapter that will allow me to use a 27c2001 ROM in the place of one of the ROMs in the PC85 Microbee as a switchable 16 ROMs. Silly but fun.

PCB

I also got some PCBs. The biggest one was a full set of boards for the Omega MSX2 which should keep me amused for a few weeks :-). I also got an amplifier I designed as well as two boards designed by Necroware.

All hail the Omega

Repairing Microbee No3 Keyboard

The third Microbee was now nominally “working” insomuch as it was booting reliably to the command prompt. Only thing is, I couldn’t test anything further without a keyboard.

The keyboard was partially working, and having removed the keycaps I could see a mix of 3 different keyswitches. White stemmed with a horizontal bar, Black stemmed with a horizontal bar and Black stemmed with a vertical bar. Without exception every single vertical barred keyswitch had failed.

The system, including a mix of keys. I have already desoldered most of the keys by this point.

Thankfully I wasn’t the first to have to fix these. Microbees have a certain reputation for keyboard failure. There is a great article on exactly how to fix them.

Out came the desoldering station, and without too much effort, I was able to get 39 of the keys out without difficulty. A small handful resisted so I left them for later. Conveniently, one of my sets of pliers was exactly the right width to grip on to the top of each keycap and remove them once desoldered.

My procedure was pretty simple. First, mark which keyswitches need desoldering with a marker. Desolder with the desoldering station, check the pins were loose, and if both pins were loose, gently lift from the frame with the pliers. Some needed an additional “suck” with the desoldering gun but most only needed one pass.

Four Down, thirty three to go.

Later, I would remove the remaining keyswitches by reflowing, desoldering and in one or two extreme cases, simply heating the solder joints while gently tugging with the pliers. Usually only one pin was still stuck so that got the recalcitrant switches.

Once all the switches were out in a batch taking them apart was a combination of terror, brute force and careful levering.

The procedure I adopted (Based on the article above) was to jam a thin flat bladed screwdriver down one side, next to the pins and lever the plastic away from the body, then jam it down besides the other pin. Finally wiggle the screwdriver sideways and down so it forced the middle area between the two already abused sections apart. Once done, you could force the screwdriver gently in further, then lever the back off the switch. At this point if everything is going right, the switch would come apart into it’s component pieces. If not, then either the plastic cracks or the back sproings off and the spring flies off, never to be seen again. Trust me, I speak from experience.

Thankfully I only lightly cracked two switches and I found the spring eventually.

Each switch consists of a body, a base of two gold plated contacts, a spring, a keystalk and a small carbon embedded contact on a strip of rubber.

Body, keystalk (with carbon contact in situ), base with contacts and spring

Once apart, I cleaned the two contacts with a soft ink eraser followed by the ever popular isopropyl alcohol. I then dragged the contact gently across a sheet of paper once or twice., followed with a dab of isopropyl. After that came reassembly followed by testing. Using a multimeter and a pair of alligator clips I tested each switch after reassembly. One or two needed a second pass, and maybe adjustment of the contact positions by gently heating them with a soldering iron. I could then straighten the pins in the softened plastic and reassemble.

A closeup of a base, showing the contacts.

Before cleaning, most had a resistance between 2KΩ and 10KΩ. After most were around 200Ω with arange from 400Ω to 80Ω. Basically a tenfold improvement in conductivity.

Once all the first wave were done (All 39) I reassembled a single key and soldered it in. Testing it worked perfectly! OK, the other 38 went back in. One turned out to be a stabiliser for the shift key so I pinched the keystalk from it for one that was broken, and used the broken one behind the shift with a jury rigged spring to provide counterpressure. (I’m not entirely happy with this. I may swap out the spring for a different type in the future,)

At this point I removed the remaining eight switches (as detailed above) and cleaned and reseated them too.

There was a little excitement when the bodged in 33k resistor array being used as a keyboard pulldown snapped a leg, (It mounts across two of the screws in a very annoying fashion) but was able to rejoin it.

Finally, I was able to test all the keys, plus loading software. Everything now seems to work correctly, within the limits of the system. This is a 16k computer with an old version of the ROMs, so compatibility is somewhat limited.

It lives! Pay no attention to the messy workbench 😀

Finally, I cleaned up the speaker and remounted everything in the lower shell.

In related news, some kind people are helping me source the one missing keycap for the CTRL key, and possibly an upper shell for it! Awesome!

Three Bee, Three Bee!

For anyone trying to follow along at home, last we saw the Microbee computers, I’d managed to make the cable for the Microbees, and proven the base 32k “Communicator” model was working fine. I’d resurrected the PC85 and upgraded it to an 85b model complete with a bunch of embedded games. Now back to the last of the Microbees, the 16k early model.

Straight up this was missing the “A” ROM, so I needed to arrange to get one. This unit used the rarer 2532 ROMs. I played around with the idea of getting some 2732s and making adapters, but in the end I found an eBay seller selling them so I ordered and waited… and waited and waited. Approximately 2 months after my order, they finally arrived. They looked a bit scabby but that was OK as long as they worked. Unfortunately I had no way of burning these models, but I had a friend who could help. I dropped them off to him and waited. Turns out both ROMs were duds. Neither would take an image. D’oh! Thankfully the seller refunded without argument (which makes me suspicious). The friend was able to find a 2532 in their parts bin and was able to burn me the ROM.

Now, at this point I have one good confirmed working ROM but that’s it. I plugged it in and turned it on and… Nothing.
Not even video synch.

Hmm. Not the end of the world. I was kind of expecting this. Next step is to clean all the ROMs and the legs from the top “Core” board to the lower “Main” board. While doing this I noticed that the last row of pins on the “C” ROM were completely missing. I can only assume at some point in the past, someone had inserted the ROM incorrectly and accidently sheared off the two pins, and then hadn’t noticed when they put it in correctly. This was easily fixed by simply soldering on some replacement legs made from offcuts from a resistor.

What’s missing from this picture?

Aaand this time we get a loud “BEEP!” from the speaker. Alright! Still no picture though.

I checked up with the various Microbee forums and someone confirmed that a beep means the CPU has started and is running code. Excellent! Now to look at the picture.

At about this point I bumped the board and suddenly got an inverted picture with a barely visible cursor. That’s promising! I’d occasionally get a screen full of garbage. At this point I knew what to do next. I replaced all the ROM sockets, the socket for the 6545 video chip and the connectors between the base board and the top board. I also cleaned the legs of every single ROM and the 6545.

I only got this a few times

No picture.

I try swapping the 6545 for a known good one and still no picture. Hmm.

Oh wait! I haven’t plugged in the video cable.

Now I’m getting a picture! A little grey but a picture nonetheless! Keyboard is rubbish but not unexpected. Let’s put it in the case and… No picture… What?

OK so something was obviously loose or failing here. I knew it wasn’t the chips as I’d swapped them over. I knew it wasn’t the sockets as they had been replaced. I pulled out the schematic and had a look at likely candidates. Next in the chain was a resistor (R20, an 82Ω resistor) or the socket the video plugged into. Both were a bit “crusty” so out with the desoldering gun and out they come. Replacements went in and… no improvement. Oho! It’s going to be one of those kind of jobs. By this point I was having to go to Jaycar or Altronics more than once a week, just to keep the forward momentum going.

The schematic.

I actually broke out my BitScope at this point and started looking for video signals, starting at the composite connector and working backward. At the composite connector there was absolutely no signal. At the connector side of R20, there was no signal. At the other side of R20, nearest the transistor (TR2, not labelled properly here) I could see a video signal.

See those dips? Every line of a composite signal starts with those.
See those squiggles sticking up? Individual pixels on the screen in white.

It took me a while to realise the signal was at a way too low voltage of about 0.3v before it went into R20. It was supposed to be closer to 1v peak to peak on the other side of R20 and it’s not going to go up at all. If I jumpered around R20 I’d actually get a picture. Could it be the amplifier transistor at TR2?

The offending video circuit area. At this point I’d already swapped out R18, R20 and was about to swap the transistor

OK so on the forums everyone thinks that TR2 is the likely suspect so back to Altronics I go.
And that makes no difference at all. Gah! I’d also swapped R18 out as it was out of spec. I’d also reflowed every single solder joint in the area and gone over the board with a magnifying glass, just in case there was a short.

Could it be the Capacitor? Hmm.

At this point, someone on the forums mentions that I must have a very old Microbee as it sounds like the video fix has never been applied. Their Microbee didn’t even have a capacitor at C20.

Video fix?

OK it turns out that MicroWorld had issued various fixes, and one of the BIG fixes was updating the video circuit with a bunch of changes. Diving into the “Microbee Hardware Notebook with Updates”, on page 63 was a complete change to the video circuit.
What the hey? I have all the components on hand. Let’s give it a go.

The revised video circuit.

Guess what? It worked!

It’s possibly crisper in “real life” than through the camera lens.

Nice stable picture, no issues.

Huzzah! Interestingly, once I got C20 (the Capacitor I was suspicious of) out of the circuit, I tested it and it was showing only a few nanoFarads. I’m curious if the circuit would have worked “as is” with that replaced, but I’d much prefer a “fixed” circuit. The picture is wonderfully crisp.

Fixed at last

The next step will be to work on the keyboard. It’s an interesting mix of three different styles of keyswitch. Desoldering has commenced.

My long term plan is to take the nicest looking of the three and see if someone is interested in trading for a “premium” disk based model, with me paying the difference. I’d really like a disk based model. Stick a Gotek in and I’d be right to load all the software I could want, without having to rely on tapes!

A huge thanks to everyone on both MSPP and the MicrobeeTechnology forum for all their help and support. You folks rock!

Fixing the Amiga 2000 (Part 1)

EDIT: See the new final paragraph for some updates.

When I got the Amiga 2000, the initial fault reported was “Dead Power Supply”, but as it had been in storage for a long time, I suspected a secondary fault of “Battery damage” may have joined the original fault. The Amiga 2000 has an onboard rechargeable battery that, after 20+ years will ooze a green alkaline solution across whatever it’s near and proceed to eat it.

Made in Germany

As such I opened the Amiga with some trepidation. As I went, I made an interesting discovery, based on a throwaway comment on the Perth Amiga Users Group. It turns out what I have is a much earlier Amiga 2000. One of the original “German” systems. These are notably different insomuch as rather than being a “big box” version of the Amiga 500 desktop system, they’re the “big box” version of the original Amiga, aka the Amiga 1000.

This leads to some limitations in design that impact what can be done with these systems.
Firstly, the 1MB of RAM is 512K on the mainboard and 512K on a riser in the slot that later models use as a CPU upgrade slot.
Secondly the chipset is very much stuck in OCS territory, and it uses the older DIP format, the same as the Amiga 1000.
Thirdly the Video slot is much truncated compared to later versions. It really only has the same signals as the rear 23 pin connector.
Fourthly the Zorro slots are unbuffered, which means what upgrades will work is severely limited.

Onto the cleaning. I removed all the cards in the card slots and the memory riser. This is where I found something interesting! The power connector had been connected incorrectly. This may be the source of the reports of power supply failure. EDIT See final paragraph.

Janus Board. Basically an 8088 computer on a daughterboard.
Memory Riser. I believe I can upgrade this to the full 1MB by populating the top row with more chips.
This shorts a whole bunch of voltages. Not good.

I removed the drive/ power supply sled and the extent of the battery damage was revealed. It did not look pretty in there. The CPU had green legs and there was a circle of about 5cm of corroded components.

(For those watching from home, this is where I discovered all the photos I’d carefully taken were all blurry! WTF camera?)

Did I mention this is a BIG mainboard?

Removing the battery was… interesting. The corrosion has a particularly bad reaction with solder to render it into something closer to a ceramic. A mixture of metal oxides and other crud.

Initially I whacked on some of my good flux, tried adding some fresh solder, and using the desoldering station with the widest nozzle. The first conductor came clean straight away. The second conductor needed a quick refresh with some additional solder to clear the rest of the way. The final, most corroded pin that was attached to the groundplane? It sat there and sniggered.
I added more solder, which pooled and blobbed on my soldering iron.
I added more flux, which rapidly turned into fancy smoke, making no change to the joint.
I scraped away the top layer of brown gunge with a small jewelers screwdriver, added a more aggressive flux, added more solder until it had a bead on it, and then hit it with the desoldering gun and… it finally cleared!

A little pressure from the other side and the battery popped clear.

This… is… VARTA!!!! (That joke never gets old)

Right let’s inspect…

Eww. C43 and C44 have ceased to be.
Solder mask flaking away
Close up
More ewww! That chip with all the green legs? That’s the Motorola 68000 CPU.

OK so I have some work in front of me clearly.

Initially I hit the affected areas with white vinegar. This has the effect of stopping the corrosion from continuing by neutralising any remaining alkaline. I gave everything a scrub with a toothbrush at the same time.

I then rinsed the whole board in tap water to wash away as much of the vinegar as I could.

Out came all the socketed chips for inspection, a quick spray with isopropyl and, if needed, a further cleaning. Most were fine but some needed attention with an ink eraser.
I’m still not convinced the 68000 will be OK. if the alkaline has crawled up the legs into the innards, it may be an ex-processor.

Next I gave the board another scrub down, this time with distilled water. I then liberally applied isopropyl and put it out in the sun to dry, turning to make sure both sides were getting sun. I redosed with more isopropyl and repeated.

Amazingly, the board didn’t look as bad as I had initially expected. I took to the traces around where the battery had been with a fibreglass pen (I hate these things. They drop glass fibers everywhere which are a skin irritant. My solution is to put a piece of paper under what I’m working on and throw the whole sheet in the bin at the end.) and cleaned up everything including surrounding vias.

Everything seems to still be intact. It’ll need a new solder mask in a lot of places, but all things considered, it’s not to bad at all. There are two capacitors that literally only exist as leads now, but I’m not sure if that was caused by the shorted rail or by the corrosion or a combination of both.

Solder mask needed.

For now, it’s going in storage until I have significant time to look at it. The corrosion should be mostly neutralised, or at least dramatically slowed. In the new year, I’ll drag this out again and begin the slow job of seeing what needs further work.

EDIT: Thanks to Stewart Greenhill for this Amiga. (I never post names without permission first)
He has mentioned that the offset rail on the PSU was post the PSU blowing up so was actually not the root cause. It’ll make this repair more interesting. I suspect my easiest solution will be to replace it with a modern PSU, plus a “Tick” circuit. (Amiga 2000 has a clock signal synched to mains frequency, the “tick”, that it uses for video timings.)