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Old 22nd Jan 2021, 7:41 pm   #219
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Right, so looking at Colin's link in #215 I would say that in the second and third captures the scope does not have a good enough GND connection to a known 0V point on the mainboard.

The waveforms on the computer board should ideally look more like the one in the first trace which you took from the calibration / test waveform output on the scope.

If the flying earth lead on your scope probe is long enough try clipping it to the lead on the right hand (-Ve) end of the big capacitor which has a cable tie around it.
I think Colin was using the resistor divider for his ground clip in #215, but from his following posts I think he knows now to use a 0v connection for the ground clip.

It would be good to get a set of scope traces for the 6502 pins that we discussed, to confirm the frequency measurements indicating the 6502 is not working, and also some practice for Colin with the scope ready for the next part of the investigation. Putting the scope captures in a doc file is a good system as it allows a brief description of what was being measure. Maybe use ctrl-print screen so only the scope window is captured.

I think Colin should stay well out of the CRT High voltages, but checking at the output of the main board is probably a good next step.

I’d recommend trying to find as many faults a possible before trying to buy more spares, I think there is more than just a faulty 6502.

Does anyone have any recommendations on a source for nmos 6502 or any confirmation that the later 65C02 or other variants could be used in this version of the PET?
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