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Old 17th Jan 2021, 6:32 pm   #138
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Non-working Commodore PET 3016

Quote:
Measured (black) pin 8 UG5-> pins 2,3,6 & 7 UG5;
0 resistance when powered off
Measured (red) pin 16 UG5 -> pins 2,3,6 & 7 and have
2.19 MΩ on 2 & 3 and 2.4 MΩon 6 & 7 when powered off
These measurements were really meant to be made on the IC with the IC removed from circuit, the reason being that if you do them with the IC in-circuit you are not only measuring the IC, you are measuring whatever the IC is connected to as well. However the fact that they all read about the same anyway suggests that none of those four pins is significantly different from the others. (which is good).

For the first set whch I have quoted above, what is the meter really saying when you make those measurements because '0 resistance' is ambiguous - do you mean that the resistance is infinite (no resistance reading)? Usually if the resistance is too great for the meter to measure it will show a '1' in the left digit, the way it does when you have the meter in resistance mode and the probes not connected to anything.

Did you try your second (originally never powered) IC with pin 7 swung out to see if that can produce 1MHz on pin 7?

I'm actually beginning to wonder if your meter has some kind of 'blind spot' for 1MHz, maybe it can't decide whether to display it as 1000KHz or 1.000MHz (This is why I was hoping you could manually select the frequency range). To check this, put everything back to normal, power up, and with black lead on UG5 pin 8, measure the DC voltage on pin 7 of UG5. What do you get... 0V? or 5V? or 2.5V?
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