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

SiriusHardware · 28th Jan 2021, 7:21 pm

What should be the minimum pin connection set which is needed to make a 6502 free-run?

-5V supply (pin 8) - 5V
-0V supply (pins 1 and 21) - 0V
-Clock in (Pin 37) - 1MHz clock
-RDY (Pin 2) (Held high)
-IRQ (pin 4) (Held high)
-NMI (Pin 6) (Held high)
-Reset (Pin 40) (Momentarily low, then held high. The reset circuit takes care of that.)

Did I get everything? If so, then let's say you take a spare 40pin socket and you snip off all of the pins (-except- the ones above) flush with the underside of the socket. Really really close, so that there is no chance that the clipped pins will make contact with anything the socket is plugged into.

Plug the modified socket into the 6502 socket on the mainboard, then plug the 6502 into the modified socket and see if the 6502 will run, with the lower address lines active, with just those essential inputs connected. If it still doesn't wake up then I think we may have to consider that the 6502 is faulty, but if it does spring to life then we are looking for something which is preventing it from working when placed in the mainboard socket.

Rather than sacrifice a spare socket, you could achieve the same aim by gently bending out all the 'unwanted' 6502 pins to the side so they hang over the side of the mainboard socket, as you did with pin 7 of UG5 a while back. However this would be a lot more pins bent on a much more exotic IC, and there is always a risk that pins may snap when you try to bend them back into shape.

Before you consider trying this, just wait and see if anyone picks up anything I may have overlooked.

28th Jan 2021, 7:21 pm	#298
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: Non-working Commodore PET 3016 What should be the minimum pin connection set which is needed to make a 6502 free-run? -5V supply (pin 8) - 5V -0V supply (pins 1 and 21) - 0V -Clock in (Pin 37) - 1MHz clock -RDY (Pin 2) (Held high) -IRQ (pin 4) (Held high) -NMI (Pin 6) (Held high) -Reset (Pin 40) (Momentarily low, then held high. The reset circuit takes care of that.) Did I get everything? If so, then let's say you take a spare 40pin socket and you snip off all of the pins (-except- the ones above) flush with the underside of the socket. Really really close, so that there is no chance that the clipped pins will make contact with anything the socket is plugged into. Plug the modified socket into the 6502 socket on the mainboard, then plug the 6502 into the modified socket and see if the 6502 will run, with the lower address lines active, with just those essential inputs connected. If it still doesn't wake up then I think we may have to consider that the 6502 is faulty, but if it does spring to life then we are looking for something which is preventing it from working when placed in the mainboard socket. Rather than sacrifice a spare socket, you could achieve the same aim by gently bending out all the 'unwanted' 6502 pins to the side so they hang over the side of the mainboard socket, as you did with pin 7 of UG5 a while back. However this would be a lot more pins bent on a much more exotic IC, and there is always a risk that pins may snap when you try to bend them back into shape. Before you consider trying this, just wait and see if anyone picks up anything I may have overlooked.