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Spirantho
22nd July 2012, 11:44
Hi everybody,

Maybe somebody here can help.
My A4000 has been unreliable for some time. I assumed it was a dodgy connector or something because I found that when I pushed on the Zorro backplane or sometimes the CPU card, it'd boot normally.... but I think now that may have been coincidence.

Anyway, since then it's got worse. I now have the A4000 on my desktop with nothing attached but a Chip RAM SIMM (known good) and the 68030 CPU card.

Occasionally, it boots. Usually, it doesn't. It just gives a dark grey screen.

Looking at the address lines on the Kickstart 3.1 ROM U176, I can see that when I cold or warm boot the machine (C-A-A works fine) the ROM is accessed for about 1/2 second, then a brief 1/4 second or so of flat line, and then usually it starts oscillating the address lines on pins 2-9 (A0-A7). Pin 1 (A17) is high at 5V. I can't read the other address lines easily. /CE is ground (active), and /OE on the ROM is inactive once it has entered this cycling state, so it must be reading something else.

I have:
recapped the board (electrolytics only). Voltage is now about 4.91V.
swapped CIAs
Re-flowed Gary and Ramsey.
Resocketed the socketed DIL chip.
reflowed the ROM sockets.
Cleaned the CPU connector.
Cleaned it again, with contact cleaner.
And again.

I also have a CS-PPC which doesn't boot in the same way but I can't reach the ROMs to test them with that; the 3630 is more convenient.

I think I need an A1200 motherboard from somewhere so I can start swapping chips around, but does anyone have any advice in the meantime?

Just to re-iterate, when it boots, it tends to work perfectly.

Thanks if anyone can help!

Buzzfuzz
22nd July 2012, 11:54
Never use contact cleaner for starters.

You could try an ATX psu with the ATX to A4000 plug from Amigakit, or make it yourself.
Weird starting problems and then running fine tends to psu problems, I've seen a few of these things happening recently myself.

duga
22nd July 2012, 11:57
Never use contact cleaner for starters.

You could try an ATX psu with the ATX to A4000 plug from Amigakit, or make it yourself.
Weird starting problems and then running fine tends to psu problems, I've seen a few of these things happening recently myself.

Or a SFX power supply if you want it to fit inside the A4000.

Buzzfuzz
22nd July 2012, 12:05
Skydivingirl's ATX PSU fitted in a normal 4000D PSU case.
http://www.amibay.com/showthread.php?t=7593

Spirantho
22nd July 2012, 12:16
Sorry, forgot to mention - this is using an ATX PSU with the adaptor from AmigaKit.
I'm using a PowerCool 450W Modular PSU here, and a Corsair CX430 at home. Both are almost new, and work fine.

PSU was my first thought too... but the lines seem to be stable, particularly the 5V one. I replaced the 47uF caps with Rubycon low ESR radial ones, by the way.

hikey
22nd July 2012, 12:20
Check the reset lines. In particular, _IORST. This starts from U141 and goes to various chips on the board.
If you've had capacitor leakage in the audio section it can get broken between Paula and CIA U350 (pin 37), and that will cause intermittant no boot.

Dragonheart
22nd July 2012, 13:26
Never use contact cleaner for starters.

Why not, if I may ask?

Buzzfuzz
22nd July 2012, 14:44
Never use contact cleaner for starters.

Why not, if I may ask?

Use it only if it's air and Isopropyl alcohol, not all contact cleaners are only with these and thus can damage the plastic of the connector.

After that give it a good dry with a hairdryer, not too close of course, and then leave it to dry for at least 2 days.

Spirantho
23rd July 2012, 18:50
Thanks for the advice!
I wanted to check the /IORST line today but I never got chance. Tomorrow, hopefully....

Incidentally, I'm not sure what the contact cleaner I use has in it to be honest, but it is designed to be used on computer connectors, and the plastic seems just fine so far. It would be a bit silly to have a contact cleaner for plastic-framed connectors if it dissolved the plastic, so hopefully I'm ok!

Spirantho
24th July 2012, 10:48
Well here's something interesting.
IORST line is a nice and stable voltage. But is 4.2V correct, because that's what it is...?

Spirantho
25th July 2012, 19:51
Guess what?
I'm typing this under OS 4 on my A4000. Cool, huh? Prometheus works, CS-PPC works, Voodoo III and RTL8029 work. All good.

The cause of all my troubles? Alice had had her connections go a bit bad. Once I'd removed it and replaced it (after re-touching some of the solder pads), the Miggy booted up perfectly and has done ever since.

Yay!

Thanks to everyone who offered help, it's appreciated!