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Cbm 2001 Pet strange boot

So, get yourself a screwdriver (or some other blunt, insulating ‘weapon’) and gently press on various chips one at a time, flexing them slightly, whilst observing what is running on the screen.

We are going to see if we can provoke a crash whilst mechanically stressing a device and a small area of the PCB slightly.

Let’s see if we can provoke the fault.

Dave
 
daver2 said:
So, get yourself a screwdriver (or some other blunt, insulating ‘weapon’) and gently press on various chips one at a time, flexing them slightly, whilst observing what is running on the screen.

We are going to see if we can provoke a crash whilst mechanically stressing a device and a small area of the PCB slightly.

Let’s see if we can provoke the fault.

Dave
Click to expand...
Just do it but nothing happens....i am sad :(
 
Don't be sad...

Today the PET may be happy. Tomorrow may be another day for it. If that is the case we repeat first the freezing and then (if that doesn't work) the flexing...

Dave
 
One problem with freeze spray, it tends to spread around to adjacent components. and can confuse the test.

One way to apply more focal & directed cooling to a particular component is to wet a cotton cue stick with IPA and apply it to the part or IC top a few times. The latent heat of evaporation cools the part down and you can keep applying it. With this method it can find temp sensitive components in crowded areas too.

It could be worth doing this in the area around the Crystal and master clock area. There is a possibility at the time of the fault that the clock was stopping. Perhaps hook up the scope to the clock and have it there running, so if it happens to crash, you can confirm whether or not the clock was the cause.
 
Yes, I did suggest that Dave monitors the clock pins as well as the SYNC pin when the beast crashed.

I am not sure whether he did or not?

I made up a little cardboard box shield (just the right size for each IC type) and use that to contain the spray to the IC of interest.

I don't see much point in using the logic probe though. If you want to do something I would suggest a bright light and a magnifying class to critically look at the soldering and pins of the ICs. Look for dry joints, corroded IC pins, contamination (especially old flux residue) and any signs of lifting tracks or other mechanical damage. Be critical!

Dave
 
daver2 said:
Yes, I did suggest that Dave monitors the clock pins as well as the SYNC pin when the beast crashed.

I am not sure whether he did or not?

I made up a little cardboard box shield (just the right size for each IC type) and use that to contain the spray to the IC of interest.

I don't see much point in using the logic probe though. If you want to do something I would suggest a bright light and a magnifying class to critically look at the soldering and pins of the ICs. Look for dry joints, corroded IC pins, contamination (especially old flux residue) and any signs of lifting tracks or other mechanical damage. Be critical!

Dave
Click to expand...
MAybe time to reinsert all original rom and waiting for freeze???
 
I find this with things that are on the edge. Sometimes they work and sometimes they don't. It took me a long while to resolve this self same unreliability with my Cromemco Z2.

Dave
 
You can if you want. But I don’t see much value to be honest. Does it error because of faulty DRAM (or associated logic) or because there is an instability elsewhere with something more fundamental?

Dave
 
Daver2, i'm desperate....pettester is still running and he never stucked!!
yet the temperature is the same as yesterday ...
 
It has been less than an hour of course...

But if you feel brave, put the correct ROMs, PIAs and VIA back and give it a go.

But, if it misbehaves tomorrow, you are going to have to revert to the ‘simple’ PETTESTER again to work on it again.

Dave
 
I suppose it's possible that the ice and spray dislodged something whch was causing an intermittent short .....

Alan
 
ajgriff said:
I suppose it's possible that the ice and spray dislodged something whch was causing an intermittent short .....

Alan
Click to expand...

I was thinking the same thing. Or flexing the board has made a better connection?

In both cases you will never know what the problem was until it returns again sometime in the future. If it has dislodged something, there is a chance it is still there lurking...

Dave
 
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