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Commodore Pet 2001-8 Stopped booting to basic.

Nivag Swerdna said:
View attachment 1312572

Oh ye of little faith.

Note pin 39 which is the CLK... is available on pin 1 of J1... which is the connector at the top. You can also get to A15 there.... that's all for people using digital signatures (as is the CLK/2)... it's a bit over the top for people doing vanilla NOPping.
Click to expand...
Sorry nivag I should have worded that better.
I double checked it as I did not know if it was a direct link from the nop to the pet logic board.
 
Just playing catch-up...

OK...

1765137040242.png


So you have verified the Address Lines... Splendid

phi2 is shown going to pin 7 but as @daver2 has pointed out this is really Bphi2

1765137584056.png

G3 is a quad NAND... two gates are used as a pair of inverters which delays the edge of phi2 as well as buffers it.

Note that pin 9 and pins 12 are pulled up to Logic 1 by R26

So... pin 13 should look like phi2... pin 11 should look like an inverted phi2 and pin 8 should look like phi2 (but 2 gate delayed)
 
Ok just measured pin 39 again and I am
Getting a very small square wave.
It is the same on pin 13 of G3
Pin 11 G3 appears to have no activity on the scope.
 

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This is inconsistent (possibly).

G3 (74LS00) devices are inverters.

If the G3 input on pin 13 is LOW, the output on pin 11 should be HIGH.

You are showing two (2) (what appears to be) LOW signals.

You are not adjusting the trace Y position between readings are you?

Set 1 V/div (on the Y channel).

Connect the oscilloscope probe tip to the ground clip.

Adjust the Y trace position to here (red line):

1765212787464.png

Take the measurement(s). Do NOT adjust the Y position again.

A TTL signal is therefore from the red line (0V) to five (5) divisions higher (+5V).

Dave
 
Here we go. First pic before i take a reading 2nd pic pin 39
 

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Pin 13 G3 same as pin 39 f3 and pin 11 G3 hardly moved at all
 

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X10 - seen so many times before! Don't worry, it is all part of the learning process 😉!

Your traces now make logical sense for the G3 inverter, but the input signal is still daft.

Can you measure something that should be correct on the 6502 CPU - pin 7 (SYNC). This 'should' be a TTL signal...

Dave
 
Spot on.

Don't adjust anything on your oscilloscope now!

OK, next points (all on the 6502 CPU):

37 - Clock in.
3 - Clock 1 out.
39 - Clock 2 out.

Pins 2, 38 and 40 should all be HIGH.

Dave
 
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