UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Non-working Commodore PET 3016

SiriusHardware · 12th Jan 2021, 2:25 pm

The suggestion for making resistance measurements hands free was based on the fact that you appeared to have a short between UG5 (7) and UG5 (8) at least some of the time. I'm not sure that is the case any more.

If:
-There is no short between UG5 (7) and UG5 (8)
and
-There is no 1MHz signal on UG5 (7)

The most likely cause of that is the 'UD' output on UG5 (pin 7) faulty, because we know the counter chain works as far as the UC (2MHz) output.

The other possibility is that UG5 is being prevented from counting up past 7 (0111) so the UD output on pin 7 never changes state. Does anyone have a handle on what's happening on the left hand side of UG5? - it looks as though it can be reloaded with 0, though I don't know under exactly what circumstances.

12th Jan 2021, 2:25 pm	#96
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: Non-working Commodore PET 3016 The suggestion for making resistance measurements hands free was based on the fact that you appeared to have a short between UG5 (7) and UG5 (8) at least some of the time. I'm not sure that is the case any more. If: -There is no short between UG5 (7) and UG5 (8) and -There is no 1MHz signal on UG5 (7) The most likely cause of that is the 'UD' output on UG5 (pin 7) faulty, because we know the counter chain works as far as the UC (2MHz) output. The other possibility is that UG5 is being prevented from counting up past 7 (0111) so the UD output on pin 7 never changes state. Does anyone have a handle on what's happening on the left hand side of UG5? - it looks as though it can be reloaded with 0, though I don't know under exactly what circumstances.