It's BIG.

As part of the pick-up I recently made, there was an Amiga A2000. This was the primary reason for the trip and was the first item offered which I gladly accepted. Everything else was a bonus - but more on that in another post.

The Amiga A2000 is a 'big box' Amiga and it is an accurate description. These things are bloody HUGE! I had expected it to be a fairly typical desktop PC size from the early 90's. How wrong I was. The main case is probably one and a half times the width and height of the Olivetti PC my brother had in the early 90's.

(Stock image from Wikipedia)

This particular A2000 came with a CD-ROM drive, two floppy drives, a memory expansion (size unknown but suspected to be 2MB), IDE controller card and a hard disk. I don't think I will use the hard disk since the Buddha IDE card immediately gives access to the use of CF card adaptors* such as those used in the A1200 and A600. Even though the CF card adaptors use a smaller pitch connector I just so happen to have an adaptor that I salvaged from an A1200 many years ago. Hoarding works. :)

*foreshadowing - CFs don't play well with Buddha

Anyway, this machine, as with everything picked up, has been in storage for a very, very long time and is in need of an initial clean before any serious work can take place. But before even that, you know what we need to do.... Get that battery out!

I see, you little git.

Once that was snipped out I could carry on and see what damage would have to be dealt with. I've done lots of A500+ in a similar condition but with the size of the board in this machine, anything could be affected. 

Clip for the 2Mb MegaChip expansion. Nice!

Top removed - fat gut for scale

With the top off the scale of the motherboard becomes apparent. Again, it's massive! Far bigger than the A500 boards I'm used to. The majority of the real estate seems to be on the left side with all the Zorro II and PC slots. And don't forget that massive power supply.

Side note - I did not attempt to switch this machine for some time yet. The reason will become clear.

After marvelling at the size of the board and case I also had a look at the keyboard. Sadly, it is missing one key. BUT, if you're a long time reader of this blog you will know I have a thing about the different types of keyboards that Commodore used for the Amiga. Well, it just so happens that this one is a real chunk of unobtanium. Firstly, it uses real Cherry MX key switches (on the cheapest, thinnest PCB imaginable - thanks Commodore). Second, you'll see from the pictures that the keyboard has two 'A' Amiga keys. They are both red. Finally, the LED for caps lock is a rectangle at the bottom centre of the key rather than a circle at the top right of the key. All this means - apparently - that this is the earliest of early keyboards and is probably worth as much as the rest of the machine just on its own.

Having been in storage the keyboard needed a bloody good clean but was really simple to do. The unit itself is held together by clips (no screws here - they'd cost too much money - thanks again Commodore). This means it was relatively easy to get apart although I was nervous about breaking the clips, this plastic is probably 30 years old after all. The keycaps were very easy to remove too and only needed a gentle nudge from the back to pop off. I suspect that's how the missing key got lost but it does look like I could get a modern blank key that will be compatible with the keyswitch or even 3D print my own.

Clean-up started - note the red 'Amiga' key..

Tea required..

Following the usual wash of keys, brush off of dust and clean with wipes, the keyboard went back together without too much trouble. One support post had broken off and was rattling around inside but a touch of super glue put that back into place.

Finally, I popped it out into the sun for a light touch of 'light-brighting'. Not sure it made any difference but there you go.

Enjoying the sun - with guest appearance by
an A1200 case

One thing I found is that the keyboard case halves are slightly bent, almost certainly due to being in storage for so long. Not a problem in itself and it's happened because Commodore cheaped out and did not use screws in the two parts of the case. Where the clips lock into place there is enough room for the halves to bend but remain attached to each other. My efforts above with the weights on each end were to try and correct that - it didn't really do much. All I need to do is put the right thickness of feet on each side and it will be fine. :)

Back to the main board.

First thing to do was to remove the damaged CPU and Agnus sockets. This was fairly straightforward and, on first inspection, there didn't appear to be too much damage around the CPU pins which was a surprise (foreshadowing...). The Agnus socket just needed replacing and there was no damage to the board from the battery in this area.

CPU & Agnus sockets removed

Insert new socket here...

Looking over the board around the CPU I spotted a via that looked to be in particularly bad shape. After a quick run over with the iron and some flux it disintegrated... Arse. Still, I have a handy reel of wire wrap wire which is the perfect size for repairing this sort of damaged. The wire has a thick (relative to the wire thickness) coating. Note that, as this particular type of wire will be important later... 

Via repaired. Others are OK(ish).

Next thing, the power supply. This is more akin to a PC power supply and has a large connector to attach to the motherboard along with multiple plugs attached to another cable for the hard disk, CD-ROM etc. I had no intention of just plugging this in. Given the length of time this has been in storage it's entirely feasible that the caps may have leaked or degraded past the point of no return. This sort of thing could lead to unfortunate voltages frying the board.

After another bit of a clean up, the removed power supply was plugged in for an initial smoke test. 

No smoke. Nice.

Next up, the voltage test.

No so nice. The 5v lines were happily pumping out 7v. The 12v line could barely manage 9v and the -12v was around +4v. This is not a happy power supply. If I'd plugged this into the mainboard and switched it on there is every chance I would have killed the board completely. 

I'm not a power supply expert so this one is, basically, headed for the bin. I have an old PC power supply which should suffice, although it is a totally different size and shape. A problem for another day.

Power supply innards - but faulty. Boo!

The only thing salvaged...

First thing to do with the old PC supply is splice the Amiga motherboard connector on to it. I should point out that the old ATX connector had already been removed as the supply had been intended for another, long forgotten, purpose. Anyway, the colours between the ATX and Amiga supplies do not match at all. On the Amiga cable, yellow is 5v, blue is Ground, orange is 12v etc, whereas on the ATX red is 5v, yellow is 12v (remember that one!!), black is Ground and so on.

More useful information on this can be found on various websites such as here or here. After the splice I carefully checked, then double checked, then triple checked I would get the correct voltages out of the supply and at the motherboard.

So, the first big switch on. What did we get? A black screen. This was not a surprise as there was still the possibility of unseen battery damage on the motherboard. Since black screen is an indication of a non-functioning CPU I put together a spreadsheet as a checklist for each of the pins of the 68000.  These checks showed that pins 34 and 41 were not connected. 

Lovely, another spreadsheet.

Bodge wires - not neat but to be 
tidied up once (if) it works

A couple of minor repairs later and it was time to try again, but this time I used the excellent, if slightly unintuitive, DiagROM. This would tell me, either on screen or via the serial port, what the state of the system was at each point during bootup.

To hook up the serial port I used a fairly standard USB to serial converter so I could use a modern PC. The last part had to be done by using individual wires with female to female 'dupont' type connectors. These are just the right size to push onto the pins of the male plugs. Only three connections were required, TX, RX and GND. TX on the PC was connected to RX on the Amiga, and RX on the PC connected to TX on the Amiga (this is pins 2 TX,  3 RX and 7 GND on the Amiga serial connector, and pins 2 TX, 3 RX and 5 GND on the PC side).

This was the result:

DiagROM serial output

This was actually a good result, even though there is apparently no access to memory. It did mean that the CPU was running the software in the ROM. 

Just for giggles, I decided to put the original 3.1 ROM back in and try again. I was surprised at the result:

Woah! I must be close!

This made me think that I was on the verge of getting the machine up and running again. With DiagROM not finding RAM my immediate suspicion fell on the logic that controlled the RAM. This had always been the problem with the A500+ machines I had repaired previously so it would make sense that the same would be true here, despite the slightly different arrangements on the board.

To verify this, I removed the following chips:

U540, U541 - responsible for the address lines

U103, U104, U105 and U106 - responsible for the data lines

Two things came from this. Firstly, one of the 74LS373 chips came out as bad and needed to be replaced. Second, many of the pads on U540 and U541 disintegrated as the chips were removed. Most of the pads affected were isolated pads on the bottom of the board i.e. their connections to other parts of the boards were on top. I assume this would be down to the battery corrosion weakening the adhesion of the pads. Certainly, I did not have this problem on other parts of the board later.

Broken.

So, after the near miss of the Guru, and the discovery of the faulty 74LS373 we must be on the verge of a successful start-up. Right? 

No.

With a new 74LS373 there was no difference in the DiagROM output. Even with the pads repaired on U540 and U541, the system could still not find any working memory. Very, very frustrating.

In my frustration I took a number of paths that proved fruitless. First, I soldered the CPU direct to the board. This made no difference. Then I tried removing the standard Agnus I'd installed to put the MegaChip back in and managed to crack the socket at one corner. F***. Strapping it back up with a cable ties appeared to work but, again, I was still stuck with no chipram detected. 

It was suggested that I needed a later version of DiagROM since 1.2.1 and 1.3 Beta had additional address validation on startup and this might help. So I downloaded the 1.3 Beta and broke out the Dataman S4 and my phone sanitiser (seriously) to wipe and re-write my current DiagROM EEPROM. But I hit a snag...

Dangnabit.

So I had to resort to eBay for the latest version. 

Anyway, it arrived and it told me, unsurprisingly, I had some address errors. 

Error...

These address errors seemed to be pointing at Address bit 11 being stuck. But despite my best efforts and many hours of tracing out traces (there's no A2000 on Amigapcb.org - sadface), nothing I did changed anything. The actual display output of DiagROM was limited to this:

Bad memory...

This screenshot was taken with the standard 8372A Agnus and J101 set to pins 1 and 2, and J500 closed. This should indicate to Gary that there is RAM in the 'Ranger' address space (apparently) hence the bottom of the screen is showing a yellow and red bar. The yellow bar is the first 512Kb of chipram and the second is the 'Ranger' RAM. In any case, it's broken still.

Annnnd, then the serial output from DiagROM just stopped. Having had some dealings with the serial chips in the A500 (MC1488 and MC1489) I knew where to look. Sure enough, after removing and replacing the 1488 - including a socket - the serial started to work again. Until it didn't. I actually worked out that the wires from the power supply to the motherboard were not making good contact. After a quick wiggle of the connector, the serial output came back. Interestingly, this course of action would also restore colour to the video output when it would suddenly decide to go monochrome - although I should point out that I was using an A520 modulator for a quick colour composite output. 

MC1488 in a socket. Not really needed
but, oh well.

By now, several weeks had passed and I had made no further progress. Except I released some magic smoke. At some point during my constant probing, I assume that I managed to short something to ground. Cue a sudden drop in video output, a large puff of smoke and a panicked leap for the power button. It was just a transient thing though, and after a quick repair, I was back to the same position, i.e. no chipram detected.

Magic smoke generator - oops

I decided to remove the sockets for U540 and U541 again as well as the CPU and try removing the repairs I had put in originally. I had reached the point where I thought that maybe I had made a mistake during the repairs.

The CPU repairs were relatively straightforward. I have a few reels of wire wrap wire which is perfect for this type of thing. As mentioned above, it's thin enough to be a trace replacement but has a relatively thick coating which also allows it to be used for 'bodge wires' without any danger of shorts.

The repairs to U540 and U541 were a bit more involved but not too onerous. I had drawn out where the pins should go and then got the multimeter on them. I added bodge wires where the traces did not seem to be making contact. 

U540 and U541 connections - what lovely handwriting..

U540 missing traces

U541 missing traces

I also went all out and replaced the Agnus socket (again) and checked all the traces from all 84 pins. Not a fun couple of hours but I did find a missing line from Agnus pin 83 - bodge wire added.

CPU pin repairs repaired. Again.

Agnus pin 83 missing link
(repaired during new socket installation)

Given that I now had another new Agnus socket I also went for it and re-installed the MegaChip. After many hours of careful, methodical repair, would this now work?

No.

Or, at least, not quite.

Garbled output - but not the usual RAM screen...

DiagROM reached this point and crashed - every time

This is the first signs of life since the Guru so many weeks ago. But what could be wrong? Fortunately, a very helpful chap on twitter suggested it was a crappy Agnus socket. I was initially doubtful, since this socket was nearly new. To eliminate it again, I took out the MegaChip and carefully bent all 84 pins of the Agnus socket out significantly further than they had been before. 

Another switch on attempt.

Oh.

My.

Goodness.

It works.

ROM screen

Early boot screen (hold both mouse buttons down)

The ubiquitous ATK from Keir Fraser

"Colours, so many colours..."

This has been a real labour of love but it's not over yet. The 2Mb zorro card expansion doesn't work and comes up as 'defective' on boot when it's plugged in. The Buddha card works with hard disks but is, apparently a real pain in the posterior to get working with Compact Flash cards. This is slightly annoying but I do still have a couple of hard disks I could possibly use. The original hard disk does still work but is quite small. I also need to hack the PSU into the space of the original without zapping myself or killing the machine...

Of course, I could just remove my PiStorm from the A500+ and stick it in this too - I think it will fit with the PI mounted to the top.

In any case, this behemoth of an Amiga is on the way back to full use. YAY!

A Good Day(ish).

Last weekend I went on road-trip to pick up some stuff from a very nice chap near London. It was a couple of hours drive to get there from the sunlit uplands of the Midlands but before I tell you what I was picking up, let me regale you with my tale of woe from the day. That way, you can decide if it was worth the trip or not.

On the way down the motorway (M5) my clutch pedal started to stick down. Not all the way, but far enough that the normal clutch travel - biting point etc - was within an inch or so of movement just above the floor. Not great but driveable. I soon managed to hook my foot underneath the pedal and pull it back up into the normal position. Sometimes the clutch would be completely normal for a bit, sometimes it would immediately stick down again. Not a major issue on the motorway as I managed a healthy steady speed.

I reached the destination, did the pickup and then set off again. With about 60 miles to go to home, the clutch pedal went flat to the floor. And I mean FLAT. No chance of getting underneath it, no way to change gear. I had to pull over to the hard-shoulder and get my hand under the pedal to pull it back up. I had some minimal clutch control again and continued.

Then it happened again..

And again..

After struggling for an hour I made it to one of the busiest local roundabouts imaginable but only a few miles from home. I needed to keep moving as, by now, the clutch was down on the floor and the only way I could keep moving was to crash the gearstick from one gear to another (not first - no chance of getting it into first). On the approach to said roundabout I was saying the desperate motorists prayer, "Don't stop, don't f***ing stop." to the traffic in front of me. You can probably see where this is going.

I had to stop. 

Car immediately stalled. Reach down and try to pull the clutch pedal up, no luck. Try to re-start the engine but it's in gear so won't start (it's a push button start). I flick the hazard lights on, into neutral, restart the engine and keep trying to get it into second while the engine in running but I couldn't take the handbrake off as I'd roll back into the cars behind me, and as soon as I engaged the gear with the handbrake on, the car stalled. 

Many people stopped to check if I was OK. Several offered to help... No. Wait. Not one single person offered to help or even stopped. Not one. After the initial queue of annoyed motorists tutted and tooted their way past me there was a bit of a gap in the traffic and I managed to get the car started and, most importantly, moving.

via GIPHY

Cue the last few miles with me being in third gear all the way, no gear changes and no stopping. Not a fun few miles. But I made it home in one piece with my pickup.

Was it worth it? Here's the list:

Amiga A2000 with unknown amount of memory and Buddha IDE card, 2 x floppy drives and CD-ROM drive

Amiga A1200 with 68030 25Mhz accelerator and 8 meg

Amiga A1200 with 68040 40Mhz accelerator and 32 meg (accelerator not working)

4 x Amiga mice (condition unknown)

Goliath power supply for the '040 A1200

Video digitiser

Colour splitter for the video digitiser

Cheetah Bug joystick

CD32 controller (original Commodore)

Misc disks and software

Hell, yeah it was worth it. :)

Multiple mice. All four now working.

68040 Card - not working...yet.

A2000 Battery - Removed shortly after this was taken

The 68040 accelerator was something I wanted to look at immediately. I had no idea what the RAM size was at this point (spoiler?). A quick examination of the board revealed some worrying burn marks on one side.

Burn, baby burn.

It's not any prettier close up..

So I removed the capacitor to give me a clear run at cleaning this up. And it cleaned up fine. I was worried there'd be some serious damage to the board but, after a generous dose of IPA and several cotton buds, it looked almost new. Very, very strange. I replaced the capacitor with a new one (47uf at 16v is about the only surface mount cap value I have!) and continued inspecting the board. 

Cleanup complete - cap removed

New cap installed

Battery. Gah. Battery begone.

No battery here (anymore). No battery damage either - phew!

The only other thing I found was that one of the PLCC chips had ridden up slightly out of its socket. A careful push down and it clipped nicely back into its socket.

I decide at this point I should probably renew the thermal gunk holding the heatsinks onto the 68040 processor. These chips run hotter than the '020 and '030 and some cooling is absolutely required although it doesn't normally need to be too extreme.

Cleaning the processor was a bit of a pain but with IPA and a bit of elbow grease I got it looking almost new and ready for some new thermal tape (due to arrive tomorrow).

In need of a clean.

That's better - ready for new thermal tape

Heatsinks will be reused so they get the
same cleaning treatment

But I couldn't just leave it. I had to see if it would now work. After wrestling it into the A1200 with wooden feet (more on that next time) I tentatively switched it on with the heatsinks resting on top of the CPU and the fan resting on top of that. I wouldn't be keeping it on for long or doing anything strenuous, I just needed to see if it worked. A 40Mhz 68040 Amiga is a rare beast these days.

Did it work?

What's that? A 68040 you say?

Oh, yes. :)

More Amiga next time.

Fix it 'til it's broke - The Third

After dealing with a broken Agnus 8375, it was time to turn my attention back to the A500+ board that was still not working.

A500+ Board from HELL

Initially, I had some very odd symptoms. The board would almost appear to boot (with a floppy drive connected). It would run through the sequence of black screen, grey screen, white screen but then no initial Kickstart screen. With a floppy drive connected the drive would show activity as if it was loading data but the screen would stay white. So something weird was going on..

First thing, I tried swapping the main custom chips, just in case one had gone faulty or was starting to fail. This made no difference. In fact, all of the custom chips worked perfectly in the Rev 6 A500 board I have (except Agnus - Rev 6 and Rev 8 Agnii are NOT pin compatible). But then I realised that the A500+ board was no longer getting to the white screen. Now, it would start at black, then dark grey then it would stop. Hmmm.

Given that this is an A500+, the board has had some previous repair, including sockets for U12 and U13. I tried swapping those chips with known working spares. No difference. In fact, things got even worse. Now the board was stuck on a black screen. Doh.

This was beginning to get a bit annoying. I had DiagROM, so hooked up the serial output to see what was happening. The initial test the DiagROM performs is very limited due to only a tiny amount of RAM being available for actual use, but it was showing errors right from the start. 

Well, that doesn't look good.

Then, in a potential case of the Baader-Meinhof phenomenon, Adrian from Adrians's Digital Basement uploaded a video where he had an A500 board (Rev 6) with a potential RAM error and he was using DiagROM to try and solve the issue. As it turned out, his video showed that he did have some dodgy RAM chips but, in my experience, Amiga RAM is pretty hardy and in all the A500+ boards I had previously repaired, I have NEVER had a RAM fault. 

In any case, I went ahead and de-soldered the RAM from my board for two reasons. Firstly, it meant I could put it in a socket, and second, it meant I could test the chips in a handy RAM expansion board that uses four of the same RAM chips with the Rev 6 board along with the excellent Amiga Test Kit from Kier Fraser. Several people on Twitter were convinced that my issues was almost certainly a similar issue to Adrian's i.e. dodgy RAM chips. 

Removing the RAM proved to be a right pain in the behind. Although the battery damage to the RAM was very limited, the solder on many of the legs had reacted with the battery chemicals meaning the solder was dull and would not flow. I managed to damage several traces due to my growing frustration and impatience. Fortunately, the repairs were fairly straightforward and more an annoyance than a major problem.

Spot the damaged traces...doh.

Repairs following my impatience.

Once the sockets were installed and the testing was complete, I was able to see that all of the RAM chips were completely fine. The issues were NOT caused by the RAM. Gah.

Sockets galore

Handy test unit. :)

By this point, several days had gone by and the board was taking up a lot of time. I was convinced that there must be a dodgy trace somewhere so I had generated a multi-tab spreadsheet (everyone loves a spreadsheet) with pin to pin connection details, listing each pin of the major chips and what they were connected to. The 84 pins of Agnus were 'Not Fun'(R). But this also showed no issues with the traces other than previous minor repairs.

One of the comments I had on Twitter came from the most excellent Jan Beta who noted that old and crusty sockets were a major source of problems on previous Amiga boards he had worked on. I took notice of this and decided to solder several chips directly to the board. The chips that received this treatment were:

• U12
• U13
• Gary
• CPU
• Even CIA
• U36 
• U37 
• U15 
• U42

Some of these would normally be soldered to the board anyway but had had sockets fitted as part of previous repairs.

Sadly, this made virtually no difference. What I did notice was that the intermittent RAM fault had disappeared. Interesting... But DiagROM would still get through the memory test and then crash.

Argh! Crashu!

Back to the broken trace theory.

No broken traces.

At some point during all the pulling, pushing, removing, installing two things happened. One, I managed to put it a RAM chip upside down. I have to tell you now that they get bloody hot when that happens. It took me several minutes to realise where the HOT smell was coming from. But the RAM chip in question survived - told you the Amiga RAM was pretty hardy.

RAM the correct way round now..

Two, it broke my 2.04 ROM. By this point I had reached the stage where the 2.04 ROM would show a black screen but the 1.3 ROM would show an immediate green screen. The reason for the black screen on the 2.04 ROM was because it was dead. Completely. Dangnabit.

But the green screen was another clue that this was down to RAM not working properly. Perhaps the Agnus chip wasn't sitting right in the socket. After a careful removal I could see that several of the spring pins in the 'economy' socket I had were bent right into the socket. Perhaps this was the issue. So I fitted another brand new socket.

Damaged socket pins?

Third time's a charm.. no wait..
Third time's a pain in the 

Annnd after all that. No difference. Green screen on the 1.3 ROM and an inevitable crash of DiagROM.

I had had enough at this point. I think I had spent the best part of 20 or 30 hours trying to make the damn thing work. Even DiagROM had stopped working properly and would only display a line of garbage at startup now.

One last ditch effort. I removed the gaggle of chips in the 'data path' i.e. U10, U11, U12 and U13 and fitted brand new sockets. Sadly, I had no 20 pin sockets, but I did have plenty of 24 pin sockets. So, given that this board is staying with me, I decided to just remove the four pins from the end of the socket and solder them on to the board. Providing the chips are inserted fully to the right there is no issue. Of course, if I accidentally put a chip in to the left I will almost certainly kill it but at least they are fairly standard logic chips, if a bit harder to come by these days due to the apocalyptic state of the world...

Shiny sockets

Following this I tried booting it up to see if I could get DiagROM back to where it was with the serial output. 

I nearly fell off my chair. The machine booted flawlessly into DiagROM. 

What. The. Heck.

I was so stunned I forgot to take a picture of DiagROM working. But it worked. I put the ROM back to a normal kickstart, attached a floppy drive with an ATK disk and tried it again.

Standby for action!

Memory! All alone in the moonlight...

So it works. Here's my theory on what was wrong. I think the original problem was that the sockets on the board had corroded/oxidised over the time it's been sat in the box. When I took the sockets off and soldered chips directly to the board (specifically around U10 - U13) I suspect I bridged one or more pins or tracks without realising. Once I took them back off the board and put the sockets on this was cured. And the brand new sockets cured the original issue.

My gut told me it wasn't a RAM fault. I should've listened harder to Jan Beta. :)