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

SiriusHardware · 14th Apr 2021, 10:42 pm

Right, so now do this bit suggested earlier.

Code:

POKE 59426,0

and then measure the voltages on the IEEE port 1,2,3,4,A,B,C,D connections - all those lines should be 0V / logic 0.

If you then

Code:

POKE 59426,255

and measure the voltages on pins 1,2,3,4,A,B,C,D again, all those lines should now be at logic 1 (~3V or greater).

If you get the voltages suggested, that will tell you that the port is working in output mode but not in input mode.

Generally speaking this is likely to be a problem with the MC3446 buffers, but we will also do checks to make sure it is not caused by UC6, depending on what the above checks find.

14th Apr 2021, 10:42 pm	#1661
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,560	Re: Non-working Commodore PET 3016 Right, so now do this bit suggested earlier. Code: POKE 59426,0 and then measure the voltages on the IEEE port 1,2,3,4,A,B,C,D connections - all those lines should be 0V / logic 0. If you then Code: POKE 59426,255 and measure the voltages on pins 1,2,3,4,A,B,C,D again, all those lines should now be at logic 1 (~3V or greater). If you get the voltages suggested, that will tell you that the port is working in output mode but not in input mode. Generally speaking this is likely to be a problem with the MC3446 buffers, but we will also do checks to make sure it is not caused by UC6, depending on what the above checks find. Last edited by SiriusHardware; 14th Apr 2021 at 10:48 pm.