A4000 boot error colours - Magenta?

[spirantho]

Hi people,

Still fighting my A4000.
Occasionally it boots, and I'm fairly sure now it's to do with the CPU connector. I've got the voltages up nicely, so that should be ok.
I've cleaned and re-cleaned the CPU connector but it's so bloomin' difficult to get at, I still can't be sure it's clean.

Anyhoo, the symptom at the moment is a bright magenta screen on a cold boot. I know the CPU is basically working because if I remove the chip RAM, then it sure enough boots to a green screen.
Very occasionally I get a white screen.
Quite often I get nothing at all - just a dark grey screen as though the CPU is doing nothing.

I've tried with both the original 030 module and the CS-PPC, same thing on both.

All this time the Caps Lock light works as it should, no error codes or anything there.

Anyone got any ideas? Thanks if so!

[spirantho]

I'll try the caps lock for longer when I get chance tomorrow.
It's the same magenta as when OS 4 boots, yes, but this is on a cold boot with just a floppy attached.

edit: it did work very occasionally earlier today but now it's just this magenta screen instead. The TV signal is displayed fine though.

[spirantho]

Well here's an interesting thing.

I just re-fluxed and re-flowed Fat Gary, Ramsey and U145, as well as using the contact cleaner on U103.

Not had a magenta screen since. In fact it's booted about 4 or 5 times with the A3630. Still no boot with the CS-PPC, and with the 3630 it often needs to be soft-rebooted after about 30 seconds of blank screen - which implies irregular voltage still. My +5V line has now been capacitated with Low ESR Rubycon caps, and the line is good at +4.96V. However, the -12V has fluctuation, and the +12V may have too, so I'm going to recap those lines too with posh caps....

Odd. I just put the CS-PPC back in and now both CPU cards have gone magenta again. Yet I'm pretty sure the CPU slot is ok now....

[spirantho]

I've already done the CSPPC. I think it's fine but I don't have another 4000 to test with.
It's gone back to magenta screen again now. I've re-socketed U103 but no change.
I've noticed that eventually it does actually go off the magenta screen. It tends to go to a magenta/black combination screen as if it can't make its mind up what colour to go, and then returns to magenta again - or occasionally black.
Here's what just happened:
Power On -> Magenta screen -> *wait a few minutes* -> Magenta/Black striped -> Magenta -> striped -> Magenta -> (C-A-A Soft reboot a few times) -> Magenta -> Lined -> (C-A-A soft reboot) -> Boot normally.

Right now it's sitting there looking at me with a friendly looking disk being inserted into the drive, as if nothing was ever wrong.

I just C-A-A again....   booted fine.

Powered off....
Powered on....
Insert disk animation (normal boot).

Surely it's a voltage problem somewhere. I wonder if the magenta screen is actually the machine waiting for the voltages to settle down still.

I've just ordered some 22uF and 100uF Rubycon caps to replace the cheap ones I was using, maybe they'll help on the -12V and +12V lines. Maybe D175 could be changed too.
And just ordered some 10nF for good measure. Maybe they need replacing too.

I just power cycled again... back to black screen. Didn't touch anything, it just didn't reboot... but I reckon if I wait a while it may do!

[spirantho]

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...?

[spirantho]

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...

[spirantho]

Just swapped it (the crystal) and it didn't improve. I had to swap it with a non-known-good one though (from a broken A600) so it's possible it's broken on both, but I doubt it. Going to fix the A600 and see if it works with the crystal to find out.

[spirantho]

I just checked the ROMS - they contain the correct data, so that's ok.
I think I'll check the connections next.... I've already tried reseating them, they're both good.
One person in that thread said that he had a similar problem with leaking caps on the sound module - that'd imply a +/- 12V line error, though, which I do suspect....

[spirantho]

Well.. I found the cause of the mysterious magenta boot screen!

One time when my A4000 managed to boot, and it was sitting on the insert disk screen, the screen suddenly went magenta again.
But what was weird was that the screen then filled with white lines.... but I could see the insert disk screen in the background!
I quickly checked Alice's temperature, to see if it was hot, and... the lines disappeared!
Let go of the chip... lines return. Press on chip, lines go. Hah!
One quick reheat of the chip with the Aoyue SMT rework station, and the problem got worse - black screen with bad sync.
Not giving up, I took Alice off completely, put a bit of fresh solder on some of the pads, put Alice back on...

Bing! Machine boots! First time! And second time! And every time for the last 30 or so attempts.

So if your A4000 doesn't boot, and you get sporadic booting with no obvious symptoms, just maybe you just need to resolder a custom chip or two.

Hurrah! Now I think I'm going to find a heatsink for Alice.....