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CBM PET 710 WITH BASIC PROBLEMS

No sorry, I had understood to check pin 22 of the "no" eprom... pin 22 of the Nop is pulsing..
 
Ah, so the CPU should now be executing instructions out of the NOP EPROM (with any luck)...

Do NOT disturb this setup.

Check all of the output pins of U31 again - just to make sure it is only U31 pin 7 that is going LOW.

Dave
 
So there is no need to measure it.

I am interested in U31 pin 7 and 9-15 ONLY.

Which of these pins are LOW/PULSING?

Dave
 
Ok, so it is executing out of the NOP EPROM.

What IC type is U42? Give me a chance to locate it...

Right, if we are accessing the NOP EPROM, we now need to look at the data bus of the NOP EPROM with one probe whilst monitoring pin 22 of the NOP EPROM as the oscilloscope trigger (- SLOPE).

We need to look for the NOP $EA instruction.

Dave
 
daver2 said:
What IC type is U42? Give me a chance to locate it...
Click to expand...
Is this...i probed U42 pins and i have problem with pin 7.... if i touch i have no signal and sometimes i see a flash of red light on the logic probe...
 

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but as you say "let's not distract ourselves" from this....let's continue with the current measures....
 
U42 is the video shift register. Totally unconnected with your problem. Although being hot is not necessarily good.

It is clocked from a very high frequency and it is highly unlikely your logic probe will work anywhere near that frequency at all!

Because of the high frequency, this will increase the power dissipation of an IC - faster = more heat generated...

Dave
 
can I turn off the computer now? I'm afraid that too much heat will burn the CPU (assuming it isn't already burnt) :)
 
Why would you assume this?

If you turn it off, you will have to get it back in this mode again tomorrow...

Your choice...

Dave
 
daver2 said:
Why would you assume this?

If you turn it off, you will have to get it back in this mode again tomorrow...

Your choice...

Dave
Click to expand...
Ok if there's no risk of some IC getting too hot and burning, let's continue with the tests...provided you have time and desire ;)
 
There is always a risk with everything...

It is getting quite late for you though isn't it - so perhaps 'call time' for tonight.

But remember, you are going to have to get the machine back in the same state again tomorrow by repeated pressing of the RESET button until (and if) you get constant activity on the CPU SYNC pin AND the NOP EPROM pin 22.

Dave
 
daver2 said:
There is always a risk with everything...

It is getting quite late for you though isn't it - so perhaps 'call time' for tonight.

But remember, you are going to have to get the machine back in the same state again tomorrow by repeated pressing of the RESET button until (and if) you get constant activity on the CPU SYNC pin AND the NOP EPROM pin 22.

Dave
Click to expand...
Ok Dave, we can continue tomorrow! Thanks so much Sir! Did you receveid my p.m?
 
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