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

Mark1960 · 1st Mar 2021, 5:03 pm

DA0 is better when UD7 is enabled, but still driving to a lower voltage than the other data lines.

I don’t see the output on DA0 when UD8 or UD6 are enabled, but still suspect there is something loading the DA0 output of the proms and stopping them from driving as high as they should.

For the spikes on the data lines, I think this is just short time pulses with a 4MHz sample rate on 20us per division. You might want to check how they look at 10us or 5us per division, just to help your understanding of what you see on the scope, but I don’t have any concerns about those.

I think its time to consider removing the data bus buffer, maybe only the one connected to DA0. Unless anyone else thinks there is something else that could be stopping the proms driving DA0 to the same level as the other data lines.

1st Mar 2021, 5:03 pm	#724
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,298	Re: Non-working Commodore PET 3016 DA0 is better when UD7 is enabled, but still driving to a lower voltage than the other data lines. I don’t see the output on DA0 when UD8 or UD6 are enabled, but still suspect there is something loading the DA0 output of the proms and stopping them from driving as high as they should. For the spikes on the data lines, I think this is just short time pulses with a 4MHz sample rate on 20us per division. You might want to check how they look at 10us or 5us per division, just to help your understanding of what you see on the scope, but I don’t have any concerns about those. I think its time to consider removing the data bus buffer, maybe only the one connected to DA0. Unless anyone else thinks there is something else that could be stopping the proms driving DA0 to the same level as the other data lines.