Fixing Amiga 4000

[spirantho]

You need to check the area around the RTC quite thoroughly. If they get confused, they can affect the reset line quite easily!
What are the voltages on the board for +5V, +12V and -5V?

I would recommend changing all the capacitors on the A4000 motherboard, especially if you're getting ripple and a strange voltage on a TTL device like that. It's not hard to do as long as you have an SMT rework station (I use a £50 Aoyue 8208 which works brilliantly).

If you really can't get it fixed let me know as I've fixed A4000s before as part of my business (usual cost is £50 including a re-cap).

[spirantho]

The other thing to watch out for is the screen syncing and the power light.
You need to watch out for the first screen sync where it initialises to a black screen, then it should make a slightly longer sync, visible on the screen momentarily. This happens when it starts successfully booting the kickstart. Yours probably doesn't do this, as if the reset line is being held low it won't get this far.

Have you checked all the traces around the SMT chips next to the battery? The tracks can look good but can actually have lost connection from the battery residue.

Changing the caps is one of the first things to do, though.

The CPU card is almost certainly fine. The CAPS LOCK procedure just checks to see if the CPU is active, not if it's working.  The keyboard has its own buffer - when this is full, the caps lock light doesn't change any more. The CPU is needed to empty the buffer, so of course when the reset line is held active (low), then the CPU can't empty the buffer and the keyboard buffer stays full and stops responding.
Does Ctrl+A+A work, by the way?

[spirantho]

4V isn't a TTL level. I'm not sure that's what you want. Having said that I vaguely remember that mine may have been like that, but I'm not sure.

It doesn't always give a green screen with no Chip RAM module in. Test it with a known good Chip RAM SIMM.

Edit: It does sound like the problem I had with a battery damaged A4000. The mouse chips U975 and U976 had a faulty chip, and one of the tracks had dissolved from the battery. Changing the chip made the CLK line tick again, which allowed the system to start working. Take a very close look at the tracks around those two chips with a multimeter, checking for continuity with the other chips in the chipset which use the SCLK line.
What schematic are you using? http://www.amigawiki.org has fantastic schematics.