1st Mar 2021, 7:43 pm
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#733
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Octode
Join Date: May 2012
Location: Perth, Scotland
Posts: 1,804
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Re: Non-working Commodore PET 3016
4.94V - same as UD7/8/9 pin 21.
I'll check the PROM.
Colin.
Quote:
Originally Posted by ScottishColin
All the PIn 20s seem to be driven from UD2 pins 14,15,16,17 (Sheet 1 of the schematics).
Should I see continuity from those pins to pins 20 on UD6/7/8/9 when the power is off - or do they only get continuity when something actually happens in UD2?
Colin.
Quote:
Originally Posted by dave cox
I think you proved earlier that the CPU was running through the whole address range (activity on A0-A15) so the PROM UD6 *should* be selected (pin 20 low) at some point. I would be following the pcb trace/continuity from UD6/20 back to whatever drives it - it will some kind of address decoder, but i can't find a handy schematic to go further !
dc
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Quote:
Originally Posted by SiriusHardware
Doesn't seem to be anything wrong with UD2, which is producing the UD6 _CS1 (pin 20) pulse that you are showing on your yellow upper trace.
With power on, can you check the voltage on UD6 CS3 (pin 21)? (should be +5V).
When you are looking at UD6 pin 11 (D2) you are also looking at UD7 pin 7, UD8 pin 11, and UD9 pin 11 because all of those pins are connected together.
The fact that you have no activity on the D2 data line when UD6 _CS1 is low is surprising. As I recall, you just about got your Arduino Mega PROM reader working. If it's still lying around, try reading UD6 to see if it is still OK.
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