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

SiriusHardware · 25th Apr 2021, 7:16 pm

Your results do sound as though there may possibly be a fault on the 6522, pin 14. To explore this further, remove the 6522 and carefully bend pin 14 outwards at an angle so that the IC can be replaced in its socket without pin 14 going into the associated hole in the socket.

Then try again with the measurement of the voltage on UC5 pin 14, both when the cassette 2 port is idle and when it is attempting to drive the tape.

When idle, UC5 pin 14 should be at logic 1, high, and when trying to drive the cassette 2 motor pin 14 should be at logic 0 / low.

When trying this, it may be that the cassette 2 motor will start running as soon as you turn the power on to the PET. If so, that in itself will be useful to know as it will mean that the motor control circuit Q3, Q2, Q1 is probably OK, but just not getting the turn-on signal from the 6522.

25th Apr 2021, 7:16 pm	#1748
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: Non-working Commodore PET 3016 Your results do sound as though there may possibly be a fault on the 6522, pin 14. To explore this further, remove the 6522 and carefully bend pin 14 outwards at an angle so that the IC can be replaced in its socket without pin 14 going into the associated hole in the socket. Then try again with the measurement of the voltage on UC5 pin 14, both when the cassette 2 port is idle and when it is attempting to drive the tape. When idle, UC5 pin 14 should be at logic 1, high, and when trying to drive the cassette 2 motor pin 14 should be at logic 0 / low. When trying this, it may be that the cassette 2 motor will start running as soon as you turn the power on to the PET. If so, that in itself will be useful to know as it will mean that the motor control circuit Q3, Q2, Q1 is probably OK, but just not getting the turn-on signal from the 6522.