A4000 040 Dead jim?

[spirantho]

Disconnect everything except the Chip RAM SIMM and the power and display. Then turn it on. You should see the screen turn black, and then a momentary sync on the TV while it resets the AGA chipset. The screen will eventually turn purple (hopefully). If it doesn't - wait some more. Wait a few minutes. Perhaps an hour. There's reset circuitry that waits for a stable voltage, and this can take a long time if the caps are bad.

Next: Turn it off and put the keyboard in. Start up the Miggy, and when it's been on for a while, press the CAPS lock key. It should light. Press it again, it should extinguish. Then press it repeatedly many times. If it stops lighting/extinguishing, then the CPU is not doing anything. If it keeps doing it, the CPU is working.

If you get any colour on the screen other than black, tell us what it is.

I had this problem with my beloved A4000 - the screen just stayed black.
After recapping it entirely, and rewiring the power supply, I eventually tracked the problem down to something more simple - it was just the Alice chip that had come a little loose from its solder points. 30 seconds with the Aoyue rework station, and it's worked 100% ever since.

[spirantho]

Incidentally, looking at your signature... capacitor failure in an A600 also manifests itself as a black screen, usually with the Caps Lock light stuck on. So if this the problem with your A600, now you know why.

[spirantho]

If I understand your psychological profile correctly (i.e. similar to mine!), there's no point pinching the FD from the 600 for your 1200, because you will want to come back and repair the 600 at some point.

[spirantho]

Schematics are your friend.

J213: ChipRAM size. Should be jumpered to ground (2MB). No, 8MB won't work.
J214: 8MB Alice. Should be set to pins 2/3 (2MB Alice)
J500/501/502: Sync on Green. Just leave them as is. Not sure what they should be, I don't think you want SoG as it has a sync signal anyway.
J852: RAM size. Set to 4MB for 4MB SIMMs (unsurprisingly). Doesn't matter for now as you should only have your Chip RAM SIMM inserted. You have tried another Chip RAM SIMM, yes?

[spirantho]

Open circuit is default, don't worry. My A4000 hasn't had a keylock since about 1999 when it was towered!

[spirantho]

First thing I would do is change the caps if you've not done so already.

You can also try powering the machine on while pressing gently on the chips (i.e. try turning on pressing on Alice, then turn off and try turning on with Paula etc. etc.).
Could be a CPU failure. Do you want to borrow my CPU board? I have a spare '030 board lying on a desk at home if you want to try it (but I want it back )

[spirantho]

Did you try pushing down on the chips when turning it on (especially Paula, if it's erratic)? You might have sit there for about a minute with your thumb on the ceramic while it tries to boot.

[spirantho]

At least give me a chance to have a crack at it before you divvy it up. A4000 motherboards are quite hard to find (read: bloomin' expensive) these days, and most of the useful parts on it you can get from a much more common A1200....

[spirantho]

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