A500, cold boot gurus?

[jimbob]

I have almost fixed an A500 which came to me dead but it has a niggling fault remaining which I'd like to track down given the damage that had previously been done somehow.

First the symptoms -

Probably ~80% of cold boots result in a guru, left click or Ctrl-A-A will then get me to kickstart screen. After this the Amiga seems to be working normally. A few different codes come up but his one is most common -

#00000000 . 00001970

All zeros in the error code, is that weird?




Next the possible red herrings -

I thought at first that the guru only appeared when no drive or terminator was connected to DF0: but I have now seen a guru with something connected so maybe a red herring.

I also thought at one point that connecting a 512k trapdoor card stopped the guru, but I've seen one in this case too. Another red herring but the cold boot crash is definitely less frequent when either or both of these things are connected. Another odd thing with the memory card, after unplugging it, I believe the guru code is referencing an address in absent slowmem. As if some signal is stuck somehow even after power off?

ie - card is connected, very rare crash on cold boot.
switch off, remove card, wait a minute, power on -

guru #00007C04 . 00C01570

Any ideas appreciated.




And finally the back story -


When I got it, it displayed only a black screen. I measured 5V and it was a little low so I thought something was sucking a lot of current, sure enough the 68k was burning hot. Presumed dead.

After replacing that I could get to a kickstart screen but not read from DF0:
Replaced Paula and could now boot from DF0:

Next I found that adding a trapdoor card caused a blue screen just for an instant then normal boot but no slowmem from the card. Replace Agnus and this is fixed.

So 68K destroyed and Paula and Agnus faulty. I have also by the way reseated other chips, and swapped around CIAs but the cold boot crash is always lingering.

So the Amiga is basically working now, the reason this is really bothering me, (apart from just not being a perfect repair), is that the board had three toasted chips so something horrible has happened to it and whatever small fault is still present could be a mild symptom of this but perhaps may have been the cause when attaching an expansion or peripheral or just randomly.

[Franchute13]

Hi Jimbob
Did you change the capacitors of the PSU?
regards

[jimbob]

PSU is not a standard Amiga one, it is an industrial type thing I keep for testing. Works great on lots of other Amigas so I think it is solid.

I am thinking of changing the two main filter caps on the motherboard though. Maybe thay are a bit tired.

[Zetr0]

@jimbob

If I could offer any advice, I would check all the solder welds on all the sockets of the board - it reads as though, due to cold starts and intermittent GURU's that you have a dry solder joint - most likely on one or more sockets.

[jimbob]

Thanks Zetr0, the solder side of this board looks really good. Nothing to see under my normal magnifier but under my wee hand held microscope, it's hard to tell, then nearly every single joint has some crazing on the surface.

I won't rule it out but will try some other things first before resoldering everything. Thing is the board runs solid once it is going, passes all "wiggle tests" too, so I'm not sure this will be it.

[bebek]

How about freezer spray and treat with cold ic's when Ami is on - one by one.

[jimbob]

Have to leave this one aside for the moment.

Freezer spray made no difference once the machine is up and running. I'm not gonna try using it on cold boots as the fault is not 100% repeatable and the spray is pricey!

[RiP]

Those errors are very similar to me. My A500 works fine until I turn off/on it quickly ~under a minute.
Hope someone can help

http://www.amiga.org/forums/showthre...t=70502&page=2