Commodore Pet 2001-8 Stopped booting to basic.

[RetroGadgetMan]

It’s the same on both without nop.

 

[daver2]

Either you have a duff 6502 CPU or there is something pulling this signal HIGH.

The PIAs and VIA will not work without this clock being present.

It also depends upon whether the RAM and ROM replacements use this signal.

Dave

 

[RetroGadgetMan]

Either you have a duff 6502 CPU or there is something pulling this signal HIGH.

The PIAs and VIA will not work without this clock being present.

It also depends upon whether the RAM and ROM replacements use this signal.

Dave

I tried another cpu and it is the same result.
I suppose a short could pull it high or another IC that has a problem.

 

[daver2]

Check on the schematic for where this signal goes and see whether those ICs are fitted or not.

Dave

 

[Nivag Swerdna]

Well at least it's not my NOPPer.

I guess leave the 6502 out for now and trace phi2 backwards...

Have you removed as many things as you can that consume phi2? PIA @ B8, VIA @ A5, PIA @ G8

Have a look at C8 pins 5 and 6



If pin 6 is anaemic is pin 5, which should be the inverse?

 

[RetroGadgetMan]

Well at least it's not my NOPPer.

I guess leave the 6502 out for now and trace phi2 backwards...

Have you removed as many things as you can that consume phi2? PIA @ B8, VIA @ A5, PIA @ G8

Have a look at C8 pins 5 and 6

View attachment 1312685

If pin 6 is anaemic is pin 5, which should be the inverse?

Yes those items have all been out with our tests.
So when I test C8 shall I remove the cpu.

 

[Nivag Swerdna]

Yes those items have all been out with our tests.
So when I test C8 shall I remove the cpu.

Yes... and No... try both.

 

[RetroGadgetMan]

My C8 is in a socket as I replaced it 2 years ago.
With cpu in place
C8 pin 5 and pin 6

 

[RetroGadgetMan]

With cpu out
C8 pin 5 and pin 6

 

[Nivag Swerdna]

Can you not tweak the time base to make it more interesting? This is a fast signal.

 

[RetroGadgetMan]

Can you not tweak the time base to make it more interesting? This is a fast signal.

Will do later.
Just sneaked this in before I go to work.

 

[Nivag Swerdna]

Please do tweak but the fact you have two lines above 5V apart looks good.

And the previous pin 39 reading makes no sense.

Once you have interesting traces also try pin 39 of the CPU socket

After that if you add the NOPPER you can also measure pin 39 on the top left pin of the connector at the left top for fun

All those should give similar traces to pin 6 of the flip flop.

Enjoy work

 

[RetroGadgetMan]

Please do tweak but the fact you have two lines above 5V apart looks good.

And the previous pin 39 reading makes no sense.

Once you have interesting traces also try pin 39 of the CPU socket

After that if you add the NOPPER you can also measure pin 39 on the top left pin of the connector at the left top for fun

All those should give similar traces to pin 6 of the flip flop.

Enjoy work

Looks like my readings this morning were D8, that’s what you get for rushing.
Her are C8 pin 5 and pin 6 with cpu in place.

 

[RetroGadgetMan]

Pin 39 of F3
Just measured its voltage. Just under 5v. Shouldn’t it be 2.5v

 

[RetroGadgetMan]

And here is pin 37

 

[daver2]

Pin 39 of F3
Just measured its voltage. Just under 5v. Shouldn’t it be 2.5v

Why?

It is a TTL signal. A TTL output signal should 'swing' below 0.5 Volts (for a logic '0') and above 2.7 Volts (for a logic '1'). See https://www.allaboutcircuits.com/textbook/digital/chpt-3/logic-signal-voltage-levels/. Anything in between 0.8 Volts and 2.7 Volts is "undefined".

I am not sure where 2.5 Volts come from.

It should certainly not be as it is. Any TTL logic input will see this signal as a permanent logic '1' (which is what G3 is).

Dave

 

[Nivag Swerdna]

I'm sorry I was being a bit slow...

So you have a good clock on pin 37...

What is happening on pin 3?

Pins 3 and 39 are signals generated by the 6502...

It would be fun to trace pin 37 AND pin 3 simulatenously

If you find pin 3 looks OK then I would be tempted to socket G3 and measure pin 39 when G3 was OUT in case it is G3 pulling it down. Is pin 39 more perky in the absence of G3?

 

[RetroGadgetMan]

Why?

It is a TTL signal. A TTL output signal should 'swing' below 0.5 Volts (for a logic '0') and above 2.7 Volts (for a logic '1'). See https://www.allaboutcircuits.com/textbook/digital/chpt-3/logic-signal-voltage-levels/. Anything in between 0.8 Volts and 2.7 Volts is "undefined".

I am not sure where 2.5 Volts come from.

It should certainly not be as it is. Any TTL logic input will see this signal as a permanent logic '1' (which is what G3 is).

Dave

My fault for doing research on Google and getting an AI answer lol

 

[RetroGadgetMan]

I'm sorry I was being a bit slow...

So you have a good clock on pin 37...

What is happening on pin 3?

Pins 3 and 39 are signals generated by the 6502...

It would be fun to trace pin 37 AND pin 3 simulatenously

Sadly I only have one X1 probe.
I will check pin 3 shortly

 

[RetroGadgetMan]

Sadly I only have one X1 probe.
I will check pin 3 shortly

Here is pin 3