Commodore Pet 2001-8 Stopped booting to basic.

[Nivag Swerdna]

Here is pin 3

Very nice. That is what pin 39 should look like.

 

[RetroGadgetMan]

Very nice. That is what pin 39 should look like.

I see. Just need to find out why it isn't.
Have I done everything that we spoke about upto this point.

 

[Nivag Swerdna]

I see. Just need to find out why it isn't.
Have I done everything that we spoke about upto this point.

^ Socket G3 and test pin 39 again without a G3

 

[Nivag Swerdna]

If you are feeling brave... Before you warm up the soldering iron...

You can bend out pin 39 on the CPU and put the CPU back in it's socket

You can then measure an unloaded pin 39

 

[RetroGadgetMan]

If you are feeling brave... Before you warm up the soldering iron...

You can bend out pin 39 on the CPU and put the CPU back in it's socket

You can then measure an unloaded pin 39

Oh my. Pin 39 unloaded.
So I guess I will remove G3 sn74ls00n next and replace in a socket.

 

[Nivag Swerdna]

Oh my. Pin 39 unloaded.
So I guess I will remove G3 sn74ls00n next and replace in a socket.

Remove; Socket; Measure before inserting a new one but with the CPU pin back in the CPU socket.

 

[RetroGadgetMan]

Remove; Socket; Measure before inserting a new one but with the CPU pin back in the CPU socket.

Sorry I didn’t see this but good news anyway as we have made progress.
I replaced G3 and now Dave’s tests are running.
Here are the results.

 

[RetroGadgetMan]

This is with nivag 8k ram back in place with my basic roms

 

[Nivag Swerdna]

Awesome

 

[daver2]

Drum roll !

Check the ROM checksums and make sure the RAM test has a good 'thrash' at the RAM.

Then start building the machine back, bit by bit, testing as you go.

What is your aim for this machine?

If you want to add a disk drive of some sort, there is a book containing a simple BASIC program you can enter to test out the IEEE488 port. I reference it quite a lot...

Dave

 

[daver2]

Just an observation (after the fact)...

G3 contains four (4) separate gates.

Two (2) gates are used to produce the buffered phi 2 clock.

The other two (2) gates are used to derived the control/enable signals for data bus buffers H8 and H9. These buffers are between the CPU and (drum roll) the RAM.

Whilst we have identified a 'hard' issue with a gate in the buffered phi 2 clock, there could also have been a problem with the other gates affecting the RAM.

Replacing G3 because of one observed problem could have fixed the other problem at the same time.

Dave

 

[RetroGadgetMan]

Drum roll !

Check the ROM checksums and make sure the RAM test has a good 'thrash' at the RAM.

Then start building the machine back, bit by bit, testing as you go.

What is your aim for this machine?

If you want to add a disk drive of some sort, there is a book containing a simple BASIC program you can enter to test out the IEEE488 port. I reference it quite a lot...

Dave

I plan on keeping it as it is. I do have two other pets with disk drives. Those pets have memory issues that I will get round too.

 

[RetroGadgetMan]

After the initial excitement of the tests running, I reinstalled H7 and 6520 turned it on to a blank screen
So something is till preventing it from booting from the roms.
Out of curiosity I reinstalled the tyenmouth rom ram substitute and enabled basic 4.
It boots to basic 4 with a flashing cursor but not with basic 1 enabled, black screen again.

These two tests are without the tynemouuth ram enabled so at least it is using the 8k ram now.

 

[Nivag Swerdna]

What sort of H7 do you have?

The H7 PET TESTER you have could be reconfigured as a H7 replacement. It actually contains many images selection controlled via solder jumpers

Obviously you should also test without the 6520 as one change good, two changes bad above... You could have confused yourself.

 

[daver2]

As I stated above ONE change at a time. There may be other faults lurking that we need to tease out - but (hopefully) nothing as bad as that horrid memory fault!

Dave

 

[Nivag Swerdna]

You should use PET TESTER to checksum ALL your ROMs. Obviously this will require a chip swap to test H7.

Obviously the 6520 is also a potential problem. These definitely do fail.

Which ROM set are you talking about? The original photos show BASIC3 with modern-ish ROMs in adapters? They should be easily testable?

 

[RetroGadgetMan]

Here are me vossi results. Looking much better. Do they look ok for the roms.
My H7 pet tester seems to have stopped working. Just a garbage screen when in location H7.
I replaced the 6520 with the mc6821p sub and the tape deck has now stopped running continuously so some progress on that front. Yay.
Which pads do I enable disable on Dave’s pet tester to give me H7. Maybe my H7 is corupt.
I can burn another pet tester and H7 if needed.

 

[Nivag Swerdna]

If you are thinking about using the H7 gadget I think you need to get it working again as PET TESTER first. Sound like you might have H7 socket issues?

You can use VOSSI to sum H7... Follow the very obscure instructions at the top right of the screen!

 

[RetroGadgetMan]

If you are thinking about using the H7 gadget I think you need to get it working again as PET TESTER first. Sound like you might have H7 socket issues?

You can use VOSSI to sum H7... Follow the very obscure instructions at the top right of the screen!

Can’t believe I did not see that lol. I have since read it in the Rossi read me file. I’ll do this when I get back.

 

[RetroGadgetMan]

So I placed the vossi test in H6 to test H7 and it passed. So all my basic roms are good.
I then put everything back in place as Pia 2 and 6522 were still out at this point turned it in and it booted. Yay!

So it sure why I was getting a blank screen.
I suspect I may have a poor connection somewhere and it may show up again.

The only original sockets left in this machine are the 6520’s 6522 and ram.

So thanks again for all your help in getting this up and running once more.
Fingers crossed it’s ok and I haven’t tempted fate in writing this post. Currently soak testing.

Frank