Commodore PET 2001-8 Question

[daver2]

There is a way of testing the pins with a multimeter set to read resistance. Set the lowest range possible on your multimeter.

Obviously, do this test with the PET power off...

Pin 1 of H4 should be connected to pin 1 of H7.
Pin 2 of H4 should be connected to pin 2 of H7.

Likewise for all of the remaining pins of the ROMs in sockets H4 and H7.

This is also true for EVERY pin of EVERY ROM - except pin 3. For example, pin 1 of H1, H2, H3, ..., H7 should all be connected together.

Try not to apply too much pressure to the multimeter probes. We are looking for a mechanical (IC socket) defect, so pressing too hard on the pins may cause a connection to be made when it was faulty. This defeats the object of the test!

If you find any issues, post them and I will have a look.

Do you have a logic probe or oscilloscope? There are better ways of testing this using the EAzy link of the ROMulan if you do!

Dave

 

[dondi]

After several thorough cleanings of H4 and H7 I get this scree, There is a blinking cursor but camera speed missed it.

 

[daver2]

Well done, operational !

Try the little BASIC program test.

Dave

 

[dondi]

Tried but now most of the KB keys are unresponsive

 

[daver2]

Ah.

But some of them are OK though?

Dave

 

[dondi]

Very few. I tried cleaning the 6520 socket and pins and initially the KB responded and then didn't

 

[daver2]

6502 or 6520?

Dave

 

[dondi]

I just edited my post!

 

[daver2]

It is more likely the keyboard itself then.

Perhaps leave it there for tonight and reconvene tomorrow?

You very nearly have a working PET 2001!

Just out of interest, do you have a tape deck or disk drive for the unit?

Dave

 

[dondi]

I recleaned the pins and seated the 6520 more firmly and all is well!

 

[daver2]

Oh well, you know where the weak points of your PET are now!

Dave

 

[dondi]

I do have the original tape deck and an external deck. I replaced the belts on both. However, the internal deck does not yet work. External one does in both ports.

 

[dondi]

I am starting to hate those sockets!

 

[daver2]

Ok, so the tape logic interfaces work OK on the main logic board then.

Dave

 

[dondi]

Talk to you tomorrow morning. I have something to do in the afternoon.

 

[daver2]

I am starting to hate those sockets!

Look on the bright side, they are not white IC sockets... They are really bad!

Dave

 

[dondi]

Yes I can attach the external deck to the main logic board tape port and it works fine.

 

[daver2]

Talk to you tomorrow morning. I have something to do in the afternoon.

And I have to go to sleep!

Dave

 

[zippysticks]

Looks like a good outcome here - well done for cracking this.
I have just got hold of a mostly non-working 2001 and have learned quite a lot from this thread. Will probably come back for some help once my ROM/RAM replacement test board arrives from futurewas8bit. Its an early '77 8K model and I'm already dreading the prospect of finding 6550 and 6540 replacements.

 

[daver2]

Monotech in NZ do a very nice 6550 replacement.

They have a 6540 coming along shortly (apparently). You can already see a photograph if you look on the website for the 6550.

Dave