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.)

Another Amiga

Yes, you read that right. I just got another computer. Yes I know what I said about peripherals. The TF1260 counts as a peripheral and I hope to be ordering more in the next few days. Meanwhile, I got offered this so how could I say no? Thanks to Stewart Greenhill for his prized Amiga!

A big box Amiga! yay!

This is an Amiga 2000, the first of the “big box” Amiga range. It’s not working and I’ll need to organise a keyboard replacement as this one is lacking that crucial peripheral. The kind gentleman who gave it to me also gave me the 1081 monitor it would have been paired with initially, as well as some key cables, a mouse and some disks.

This unit also includes a Janus PC Bridgeboard, that allows the system to run PC compatible software, albeit, very slowly. It also has an MFM HDD, I’m guessing of around 20MB of capacity. I won’t hold my hopes out for that after 35+ years.

Possibly most worrying is that the original onboard battery is still onboard and the motherboard shows signs of corrosion. I’ll need to strip it, and give it the old 1.2.3. of Vinegar, followed by Distilled water followed by Isopropanol.

The monitor has a bung switch, but that is typical of these monitors, and I already have a replacement switch somewhere I can use to swap it out.

All in all, a nice pickup, although I suspect it’ll be quite the project to get from here to the “insert workbench” screen.

My last question though is “Where the heck am I going to put it?”

Have I mentioned how much I like having a 3D Printer?

One of the other things I picked up at the PAUG meet on Saturday was a ROM Switcher for my Amiga 600. This simply comes with a pair of small switches to choose between 4 different possible ROMs.

(It’s currently set to switch between Kickstart 1.3, 3.1, 3.2 and DiagROM but I want to swap out 3.2 for 2.5 as I don’t yet own Workbench 3.2)

Now as I’d removed the RF encoder, I had a perfectly good place to mount the switch.

I ran up a simple model in OpenSCAD, exported it as an STL, imported that into my slicer and thought “Wait! the time factor here will be in the printing and the height is quite low.”

Thus, I printed 5 versions of the model, all in 1% increments and decrements from my initial model. (So 98%,99%, 100%, 101% and 102% scaling)

3 of the 5

They came out great, and I’m finding a bit more care with my print cleaning gives me much more consistently good models. Best of all the best fit was the 100% model. I’m amazed!

In situ.

The fit for both the switch and the mount into the Amiga are tight friction fit. They aren’t coming out from external, which is exactly what I wanted.

Shaving Amiga Yaks

So last night there was a Perth Amiga Users Group catchup I attended, which was awesome fun.

The Beyond Retro team playing a game they’re working on.
Not Amigas, but VERY interesting nonetheless. A pair of Vectrex vector consoles.
Look! Amigas!

I, er, may have gone a little insane in all the excitement.

See, I bought something. Something terrifying and powerful and…

No, not the one ring!

It’s called a TerribleFire TF1260 and it’s a VERY fast, VERY powerful upgrade card for the Amiga 1200.

Let the Terrible Fire out!

This is running a 50MHz 68LC060.

To give it some context to the PC centric heathens out there in the audience, this is like going from a 286 with 2MB of RAM to a Pentium with 128MB of RAM.

It’s quite some upgrade. The TerribleFire cards are the result of work by an extremely gifted electronic engineer by the name of Stephen Leary. They’re open source and I sourced mine from RetroKit.

I currently have it working but there was some effort to get it there. Have I mentioned my Amiga 1200 is not in a case? I do have plans to make a custom cut case for it.
(Would anyone be interested in an article about that?)

Here’s my Amiga 1200. Note the complete lack of case.

First up, when I initially plugged it in, it was a decellerator, as the Amiga refused to boot. This was fixed by applying some deoxit to the edge connector followed by an ink eraser.

Next up, while the machine would happily boot into a plain workbench disk, it wouldn’t boot from the HDD. It would throw up Guru Meditation errors. After some great advice from Matt and David on the PAUG forums, I installed the MMULib and had it happily booting to an Amiga 3.1 Workbench.

There was a little more mucking around until Matt pointed out I could bypass the warning message on SysInfo to actually run it with an ‘060 in there.

Turns out if you just press the mouse button this just works regardless.

Why SysInfo, you may ask? Because it’s the gold standard for irrelevant benchmarks that prove nothing and are of dubious value. And in that spirit here are the before and after shots.

BEFORE
AFTER

That’s some upgrade! Hopefully by the time I get around to building the case, I’ll be able to use the onboard IDE port to connect to an IDE CD-ROM I have earmarked for the system. At that point I will truly have the Amiga of my dreams 😀

Trying not to get discouraged

So it’s been a frustrating week of stuff not getting fixed. The kind of week where the hobby feels more like a “job” than “something fun”.

Firstly the Archimedes is still having problems with the floppy disk, despite me swapping out the 74HC574. I will need some time to put it on the bench and properly investigate the root cause. In the meantime, the Archie will have to sit in the naughty corner, or, in this case, the plastic tub of shame.

After that failure, I decided to recap the Amiga 600. This went surprisingly well. I recently got some more tips for my TS100. These were a KU tip and a JL-02 tip. The former is like a knife blade, and is great for drag soldering and anywhere where lots of heat is needed. The latter, on the other hand, may be one of the most useful soldering tips I have ever used. It’s a long, delicate tip with a curved end. It’s not great for heavy heat transfer, but for delicate work, it’s amazing!

There were four capacitors wedged hard up against plastic fixtures, that I had been unable to desolder. With a little foil and polyimide tape, and the long thin tip, I was able to successfully solder all four caps without any grief. In fact, those were probably the two capacitors I was most happy with.

The rest proceeded uneventfully, except for one cap being in backwards. (Always check your polarity before you turn on. I did, and spotted the offender before I turned on, thus avoiding blowing it up. I quickly removed it using the two iron “Chopstick” method and resoldered it.)

Once it was fully recapped, I powered it up and success! I had a system patiently waiting for a disk.

I had ordered a IDE to CF Adapter so I thought “Let’s see if I can get this installed?”.

This is where things started to go wrong.

I initially set up the CF on an USB to IDE adapter, connected to an Amiga emulator, and after some false starts, I was able to get this booting happily on the emulator. As soon as I tried to get it to boot on the real hardware it would simply be ignored.

In desperation, I cannibalised the Gotek out of my BBC Master system, and tried installing directly from Workbench images directly from the A600 itself. While I could recognise the CF card and partition it to my heart’s content, I could never get it to actually show the drive on my desktop so I could format / boot it.

I tried two different CF Cards. No luck. Eventually Matt on the PAUG forums pointed out there was a bug in the version of the Kickstart ROM I’m using that makes it incompatible with hard disks bigger than 40GB. Huh. The smallest CF I have is 64GB, and that one isn’t seen as a Hard Disk. I guess I’ll need a new Kickstart ROM.

All in all, a frustrating week, despite the success with the recapping.

The board, Sans capacitors. Amiga motherboards were named after songs by the B52s, this one is “June Bug”
First capacitor in. Note the lack of clearance.
Second capacitor in! They were NOT fun to solder in.
Third and fourth. After these four, it got a LOT easier.
Only two through hole capacitors left to go on this section.

A week of leave, a week of retro goodness!

What a wonderful thing a week of leave is, especially if you have nothing planned, except your hobby.

I deliberately left myself plenty of time for just mucking around. I set myself three project goals, with some option “stretch” goals.

  1. Work out what was wrong with the floppy drive on the Archimedes.
  2. Decap the Amiga 600
  3. Print a 3D case for the Creativision Megacart

Archimedes

I got the Archimedes on the bench pretty much Friday evening and it stayed there for most of the week. The first thing to do was to completely strip it down to just the motherboard, the PSU and the CPU riser. That way I could have a look at what was going on with all the signalling.

I must put a big thank you to the StarDot forums, who, as always, were invaluable in their assistance.

Breaking out the logic probe and the schematics, there seemed to be 3 prime candidates that could be the cause of the fault.

  • IC47, a 1772-02 Floppy drive controller chip. This was a very commonly used chip for this era. Also used in the BBC systems among others.
  • IC38, a 74LS05 hex inverter. This is used as a simple inverter buffer. The prime candidate!
  • IC29, a 74HC574 flip flop. Not quite sure what this is doing, but it ties into several key drive pins.

I started with IC47, and initially I thought this was the most likely candidate. I could see data going in but no data coming out. Turns out I was looking at the wrong pin! Oh well, the spare I have ordered will be useful somewhere else I am sure 😀

This one was fine.

Next I moved onto IC38. Now these fail all the time, which is why I probably should have checked it first. The only reason I didn’t was a gut instinct. The logic probe showed this chip was happily inverting just as it was supposed to.

This one was also fine.

This left IC29. Now I don’t really understand how this chip is supposed to work, but simply looking at activity, I could see data coming in on the input side, but nothing coming out of the output side. Everything was locked. The Drive Select pins were all being driven continuously and the Motor pin wasn’t being driven at all. This could explain the lack of any activity.

Having a likely suspect, I carefully desoldered the chip, using my desoldering station to remove the majority of the solder, and my brand new hot air rework station to carefully loosen the remaining solder. Popping it out, I stuck it in my TL866 II+ and ran a logic analysis over the chip which promptly failed! That seems to vindicate my suspicions. Unfortunately it’s not a chip I can buy from any of the local suppliers, so I have one on order. In the meantime I’ve stuck a nice machined pin socket in there to make the next step easier when the part does arrive.

A machined pin socket, ready for the replacement chip.

Amiga 600 decap

The Amiga 600 still had 4 capacitors I’d been unable to remove due to the limited room around the remaining capacitors. All four were relatively “flush” up against an existing component. I had attempted to remove those components, without much success, so I was at the point where I needed newer tools, and finally I had a hot air rework station.

The four silver strips mid picture were where the capacitors were. The components above and below are soft plastic and are heat sensitive. I used lots of polyimide tape and aluminium foil at this point.
Two more horrible caps removed. Right up against that coil above.

As this was a new tool, I practiced on an old PC motherboard until I was comfortable with my work. I certainly managed to “pop” a capacitor that turned out to be through hole, not surface mount, but that board had loads of bent pins so I didn’t mourn it much. It did vindicate my basic approach. Slow air, 380 degrees for leaded solder, lots of polyimide tape and aluminium foil insulation around the temperature sensitive components near where you are working, and slowly slowly does it.

I gently heated the general area, trying to heat the board evenly as to not warp it, and at the same time raise the temperature of the components. Eventually they came free with only a light pressure on the tweezers I was using to gently lift the components with.

With this technique I was able to remove the remaining four capacitors. Replacements are on order. Soldering these components back in? That’s a problem for “Future me”. I suspect a delicate tip on the iron and, again, loads of polyimide tape and aluminium foil.

3D Case for the Megacart

This one was mostly me in front of a computer with OpenSCAD and lots of trying and trying again. The Madrigal Design forums had several people assisting here, with a BIG shout-out to Tom over there who managed to print a cartridge before I’d even had a chance to get mine on the print bed. It allowed me to rapidly iterate two new versions based on his feedback. I’m already contemplating yet another iteration, to add a way of securing things a little more robustly.

Once I had the designs in OpenSCAD, I was able to export as STL, then feed them to my slicer and begin printing.

These are a little too big for my resin printer, so I need to print one part on its shortest edge and another on it’s side. This means the prints take 8 hours and 5 hours respectively. If I had a bigger print bed I could print them directly on their faces, which would drop the print time down to much closer to under two hours.

(If it’s not obvious, the slowest part of printing with a resin printer is resetting the z axis. Anything that is larger in the z axis takes longer, so you usually try and align your models to be largest in the x and y axis)

The quality of the top was… OK. I think I need to get better at leaning my models. There’s some smearing that I think is improperly cleaned resin that rehardened.

Unfortunately the base failed completely. I need to review my print settings and reevaluate to see what went wrong. I don’t think it bonded properly to the print bed.

It emerges from the vat!
The top section. I think adding internal supports may help in future.

Afterword

The moral of today’s episode seems to be – You don’t need additional tools until you do, and then you wonder how exactly you lived without them beforehand!

Now I have hot air, I think the next tool I will want to get will be a proper bench power supply with adjustable Amperage, Voltage and probably two voltages at once. That may be something for next year, though.

Broken Archimedes, Working 3D printer

No post last week. I got busy with non “retro nerd” stuff and didn’t have anything to post.

So far this week has been a lot more exciting.

Poor Archie

My Archimedes 440 has decided that, no, it no longer wants to read Floppy Disk images. This has kept me occupied for most of the week, on again, off again. The symptom is every time you try and access the floppy drive (real or Gotek), there’s no motor activity, no drive lights and an error of :
Error from ADFS Filer
Drive Empty

Which is not great. After checking the obvious stuff (Make a real FDD image just in case, check files on the memory card have the right config file, check cable, check power, make sure the Gotek is powering itself up and allowing images to be shown) I got to the point where I knew I was going to have to disassemble the whole thing and break out the Logic Probe for further diagnosis.

This is a not insignificant undertaking as the Archie has a lot of different screw sizes mounted all over the system. It’s also awkward and heavy.

There were SO MANY screws in this.

I girded my loins (metaphorically) and got on with it. Now it was out of the case and laid out neatly on my workbench, I was able to get out the logic probe and “have a look” at the state of various lines. There were some obvious candidate places to look, but I stared with the FDD cable itself. Probing around the Gotek connector, there didn’t seem to be a whole lot of life. All the pins were being held either high, low or in one “special” case as floating. Turns out that was a “Not Connected” pin in the standard, so that’s OK I guess.

Right, no activity there. Let’s move further upstream. The next easiest chip to check was the FDC Chip, a VL1772-02 Floppy Drive Controller chip.
This is where things got interesting.

I ran across all the pins with the logic probe. There was definitely some data on some of the pins. Interestingly the place there didn’t seem to be any activity was on the output pin (Pin 22, WD) to the floppy. Could it be a bad FDC?

I checked the buffer inverter chip sitting between the floppy cable and the FDC chip. Each pair was suitably inverted from the input, so at least I could eliminate that.

I’ve ordered a replacement chip from Exxos UK as they have them for an extremely reasonable price. One of the forum members over on the Noel’s RetroLab Discord suggested them and OMG were they cheaper than any other source I was able to find. Exxos also has an excellent reputation, and I’ve been a member of the forums for quite some time.

Three Dee Printed Goodness

So the reason I discovered my Archimedes was unwell is I went to use it to fire up a new joystick interface I was building. This is a very simple interface with only a handful of diodes and a DB25 male connector, plus half of a Playstation extension cable.

A handful of diodes. My soldering has improved in leaps and bounds over the last few years.

I had got the bits together, soldered up and assembled in a shell when I looked at it and decided that the hole at the back was just too ugly to be allowed to live. The cable flopped around. This could not lead to good long term reliability.

When you have a 3D printer, everything looks like it needs to be printed in 3D 😀
This also gave me a chance to play with Fusion 360, a package I am learning slowly.

A few minutes using CorelDRAW to prep the primitive to convert in Fusion 360 into a model to import into the slicer software and I had a thing. Today I was also a lot more organised than I had been for my first print. I had good gloves, I had organised my workspace and I was comfortable prioritising what needed to be done and when it needed to be done by.
My prints got rinsed in a timely fashion and not for too long, cleanup was easier and overall everything was just so much smoother.

Oh boy does it show in the prints.

My first prints had an almost chalky feel to them. These are glossy, smooth and rock solid.

The finished product is just great!

That cable is not going anywhere
It’s a friction fit!

The Shape of Things to Come

I have a hot air rework station now. I plan to teach myself to hot air desolder over the next week. I will be practicing on some old “junk” motherboards, before moving onto finally decapping my Amiga 600.

Achievement Unlocked: 3D Printing

Over the last few weeks, I’ve been accumulating all the “bits and pieces” to finally properly use my 3D printer. Today everything came together and I finally printed my first 3d print!

Printer in action!

It’s a little holder for the rotary encoder and OLED display for a Gotek drive. I often mount them externally on some cable, so that it’s easier to access the buttons. This is particularly useful for things like the Archimedes where the Gotek faces the rear or the Amiga where it connects through the side. No more having to peer around to read the display 🙂

It’s not perfect, but OMG it looks nicer than I expected!

Ignore the gap at the bottom. I have fixed that with a dab of superglue.

What would I do different? Probably some sort of clasp for the front and a bigger, more robust hole for the screws at the back. The Rotary encoder bit wasn’t quite right. Other than that, I’m very happy.

Total print time was 45 minutes for the base and 4 HOURS for the top.

I’ll release the SCAD files once I have made the corrections.