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

SiriusHardware · 8th Mar 2021, 9:35 pm

A percentage of difference between one line and seven others which are theoretically identical to it could turn out to be significant, so we'll remember that anomaly for the future.

Each of those pairs of UI10 / UI11 pins is in turn connected to a pair of DI/DO pins on two of the 4116 RAMs, so you have a total of 6 IC pins connected to each of those circuit nodes. If you have one out of the 6 pins faulty and five normal, that could certainly shift the reading away from what is 'normal' on the other, similar nodes.

A quarter of a volt is quite a significant difference between your 'gold standard' 0V and the supposed 0V in that area of the circuit. With power off, can you measure the resistance between some of the RAM IC pin 16s and your usual 0V point? It should be very, very low.

8th Mar 2021, 9:35 pm	#834
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,567	Re: Non-working Commodore PET 3016 A percentage of difference between one line and seven others which are theoretically identical to it could turn out to be significant, so we'll remember that anomaly for the future. Each of those pairs of UI10 / UI11 pins is in turn connected to a pair of DI/DO pins on two of the 4116 RAMs, so you have a total of 6 IC pins connected to each of those circuit nodes. If you have one out of the 6 pins faulty and five normal, that could certainly shift the reading away from what is 'normal' on the other, similar nodes. A quarter of a volt is quite a significant difference between your 'gold standard' 0V and the supposed 0V in that area of the circuit. With power off, can you measure the resistance between some of the RAM IC pin 16s and your usual 0V point? It should be very, very low.