Need Help with my Amiga 4000

[slammers]

I have a 4000 (non-tower) that has been sitting around for years and decided to try and fire it up. Unfortunately it just gave me a blank screen. I checked the battery and it had a minor leak so I removed it and inspected the PCB and could not see any signs of damage.

I unplugged the HDs and Floppy powered it up a few times. On one occasion it actually booted and gave me the screen saying 3.0 Roms and the animation to insert the Workbench disk.

So I plugged in the floppy and tried again. It took quite a few power cycles but managed to get the boot screen again and load up Workbench 3.0 off floppy. It showed I had my full 2mb chip ram and 8mb fast ram. I browsed the disk and everything seemed to work. It worked for maybe 15 minutes and then the pointer froze. The screen remained active.

So I then plugged in my HDs to see if I would get lucky but unfortunately I have not been able to get it to work since, even unplugging all the peripherals.

The keyboard seems to work, the caps light blinks when I power up. If I press Ctrl-A-A the light blinks and the HDs cycles.

The motherboard looks very clean. There is no sign of bulging or leaking caps. I used meter to check all the electrolytics and none had shorts. I guess they could still be bad but there was nothing obvious

The power supply seems ok, I get 5.08V, 12.02 and -11.96. According to my scope they are all nice an clean. No ripples of any kind.

I could not detect any noticeable hot spots. The Alice chip gets a little warm (36C) but not extreme.

So I am looking for some advice on how to proceed. I am a little confused on the color sequence, when mine did work it only went from black to dark gray before the bootup menu appeared. Does the 4000 go through all the startup colors?

Since the screen stays black is that a sign of the processor not detected? Is there a signal I can probe that would indicate whether the processor is detected?

I put my scope on some of the Zorro slot pins and see activity. C1 and C3 are 3.57Mhz.

I also have an Amiga 3000 that does work. Is it possible to plug the A3640 expansion card into the 3000 to see if that board is the problem?

Thanks for any help you can provide.
Shawn

[SACC-guy]

My guess is that the cpu board had worked loose and might need cleaning and re-installing correctly..

[slammers]

I did that when I removed the battery from the mother board. Also re-seated all socketed ICs including the ROMs, the 68040

I have removed and reseated the A3640 multiple times.

[kirk_m]

Color codes are not all they're cracked up to be, IME.

But, yes, upon booting up, it is normal for the Amiga to go from black, to a dark grey once the video syncs and the machine starts to boot.

Look at the CPU slot under magnification (as well as the connector on the 3640 itself) and make sure none of the little pins inside have gotten bent.

Are you getting any activity on the _DS and _AS lines on Buster?

[Kremlar]

Post some pics of the battery area.

[darksun9210]

agree on the battery thing as first point of diagnosis.

yes you can plug the A3640 board into the A3k. they were a cheap upgrade for 030 machines for a time when A4000/040 owners were upgrading and selling off their A3640 boards. Plus it's not a bad idea to rule that out as a point of failure, but.
it is a bit of a slog as the A3k's CPU slot is under the drive tray/carrier - that is only easiest to remove after taking the PSU out.
also you'll have to play with some jumper settings on the A3k to switch clocks to the CPU board to get it to run off the installed CPU board rather than the internal 030.

another thing that might be worth doing if you can get one cheaply and easily enough is an A4000 to ATX psu adapter - rule out any power problems. check the ends of the power leads going into the mainboard that they aren't corroded or burnt.

pull out all fast ram. pull everything you can. get your machine to a basic working state first, then start working your way back up. My A4k resurrection process i recently went through to bring mine back to life - i ended up figuring out that all 4 of the fast ram sims i had installed on the board on it were dead or not-trustworthy. Somehow my DVDrom drive was toast aswell.

if your A4k is one with a simm slot for chipram, see if you can get some life with a different simm in there?

i wish you luck on your journey!

[slammers]

I did some more research and I have the rev 3.0 A3640 board with the issues with C105 to C107 being backwards. I checked these caps and they were not leaking but I changed them out and corrected the polarity.

I did notice the C102B and C102E were leaking. So I replaced those as well.

Unfortunately it still would not boot.

So I looked at the 200 pin Local Slot connector under a microscope and I could see some form of contamination of the gold plated contacts. It looked very odd. So I cleaned that up with some contact cleaner and that seemed to fix the issue. Now have a working 4000.

I am not sure if the video is working completely though. I can use my Commodore 1080 to get to workbench but when I run some apps the screen goes black. If I do some mouse button magic I can get back to the workbench. If I drag the workbench window down, there is a window behind it that is grey and has random black pixels everywhere.

It may just be that the video is running at a higher rate than my monitor can handle. I have an NEC Multisync 3D that I am sure I used on the 4000 but I seem to have lost my Commodore DB23 to DB15 adapter. I have EGA to VGA adapter but that does not seems to work (DB23 to DB9 cable -> DB9 to DB15 adaper, -> NEC VGA cable from monitor). I suspect the pin outs with this combination are just wrong.

Is there a connection diagram for DB23 to VGA available so I can make something up?

[darksun9210]

Glad to hear you're back up and working

i found this. but it looks deceptively simple
http://wonkity.com/~wblock/a4000hard/connvga.html

[slammers]

Thanks a lot. I found another a something myself but did not indicate the buffers for the sync lines.

I will make one of these up once my DB23s arrive.