A4000 boot error colours - Magenta?

[paul1981]

Sounds like it could be bad motherboard capacitors. Have they been changed? If they haven't, then remember they're 20 years old now. Just a thought.
Another thought would be the main oscillator on the motherboard (28MHz on A4000?). I've never had one die on me before, but it is possible. I know they can go flaky and sometimes die completely, so it's something else to consider.

[paul1981]

The electrolytics have all been changed. So far I've changed all of them once, and then I changed the 47uf (the ones on the +5V line) with low ESR Rubycon ones. I've got more Rubycons on the way for 22uF and 100uF.
The oscillator is fine, because once it starts working it continues to work fine - until I turn it off.
I think you're right, though, it must be the caps, surely.
Interestingly, the +12V_USER rail is at 11.65V - I wonder if that's enough.... the PSU is giving out +12.4V, but the other side of D175 is only 11.65V. Is that normal...?

I don't know what D175 is, but if there's no hard drives attached then I believe that the +/- 12V rails are used for the audio amplification circuit only, so I wouldn't count on the 12V line being important at this stage.

The oscillator is fine, because once it starts working it continues to work fine - until I turn it off.

If all else fails, and you've replaced all the caps, then you could try the oscillator as a last resort. Maybe sometimes it just doesn't start up correctly. Small chance, but you never know your luck. You could try reheating it before replacing it. A couple of months ago there was someone on here with a Blizzard1230IV which had a dry joint on its oscillator.

[paul1981]

I wish it were as simple as the oscillator! If that were the case though then the CS-PPC would still be working, as that uses the external clock.
D-175 is the diode seperating the PSU's +12V line and the usable +12V_USER line. It's got a voltage drop of about 0.7V which I think is correct.
I think again you're right about the +12V line being just for the audio amp, but I believe the Amiga checks for a steady +12V rail before booting doesn't it? This is the usual cause of A600s not booting, I believe. It certainly looks like this is what's happening, anyway...

The 28MHz clock is required for the custom chips and video circuit. This is always in use whether you have an accellerator card or not.