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

SiriusHardware · 30th Jan 2021, 2:46 pm

We have a theory that the CPU may be reading one of several 'illegal' opcodes from the system databus which are able to put the CPU into a 'trance' state in which it appears inactive.

Although it is also possible that a databus line stuck high or low could cause a similar problem, random or progressive reconnection of the data bus lines won't really help us much, although I can see where you are coming from. There would be no harm in trying it, though.

Edit: Crossed with Julie. Colin has already reconnected all of the address lines to the address buffers and the CPU still runs, albeit with the databus lines still disconnected. We're now asking him to scope the address lines before and after the buffers to verify that the buffers are actually functioning as buffers.

30th Jan 2021, 2:46 pm	#365
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: Non-working Commodore PET 3016 We have a theory that the CPU may be reading one of several 'illegal' opcodes from the system databus which are able to put the CPU into a 'trance' state in which it appears inactive. Although it is also possible that a databus line stuck high or low could cause a similar problem, random or progressive reconnection of the data bus lines won't really help us much, although I can see where you are coming from. There would be no harm in trying it, though. Edit: Crossed with Julie. Colin has already reconnected all of the address lines to the address buffers and the CPU still runs, albeit with the databus lines still disconnected. We're now asking him to scope the address lines before and after the buffers to verify that the buffers are actually functioning as buffers.