About Dave's PETTESTER (trying to diagnose another issue....)

[giobbi]

Hi Dave,

Suddenly my 8032 stopped to display the image on screen. It does the usual chirp, but I get only a black screen.
Defined that the CRT is working, I decided to use your pettester (edit) and - surprise! - it's displaying the usual test pattern on the screen.

(sorry for the scan lines etc, I raised the luminosity to be sure the CRT is working)

At first I supposed my EDIT eprom was burnt, so I programmed another one, but of course it didn't work.

Since the PETTESTER is working, I would say the Kernel is ok too. The basic 4 @ $C000 (901465-20) already is an EPROM with a socket adapter, so I tried it too, but nope. The last one is still a ROM, so I should make another adapter (no problem at all, of course) but first I wish to know if you have any idea about what it could be... You wrote the pettester, so you probably know well why the video output is working with it but not with the EDIT (ep)rom (remember: it's doing the chirp!)

thank you!
Giovi

 

[eight088]

The checksum for D rom is different to what is in the manual for the pettester. I'm not sure what role that particular rom plays, but maybe its crashing the system? I wonder if this is your issue? Maybe try and burn a D rom if you have the correct rom chip and try again.

 

[daver2]

Yep, something looks wrong with your $Dxxx ROM. The checksum is not correct for BASIC 4.

The fact that my PETTESTER code runs only indicates that a handful of instructions actually work in the $Fxxx ROM. The checksum being correct is the key thing once it does run.

Also, the keyboard values are all 'ff'. They should be '00'. Have you removed any of the PIA's (especially the keyboard PIA)?

Dave

 

[giobbi]

Gosh! I did not even remember there was a PETTESTER manual... and I had it!
Now everything becomes easier...

So I fixed the $D000 ROM, and, surprise...

now the $B000 is wrong!

So I also replaced the $B000, and finally the ROMset is ok.



it didn't boot yet, but I removed the 6520 and it comes to life (without cursor, of course). So I put a "modern" replacement (6821 instead of 6520... I'm sick and tired of old, unreliable MOS ICs...) and now it works like a charm.

I'm not sure what kind of storm hit my poor PET, but it's sunny again now. Thank you guys, you helped me a lot!

 

[daver2]

Yep, there is a full PETTESTER manual !

You haven't got white IC sockets have you?

Dave

 

[giobbi]

Yep, there is a full PETTESTER manual !

Yep, and I already had it on my PC, but I had totally forgotten about that!!! What a shame, if I read the manual I didn't need to ask help... But the truth is that I have so many stuffs on my PC that I can't remember all (but I should have remember about the pettester manual, since I'm sure I already used it in the past...)

You haven't got white IC sockets have you?

If you mean the white, unreliable commodore sockets, the last one remained on the board is the one of the EDIT rom. Actually I use to change all the old CBM sockets, but this one escaped... for now LOL

-- Giovi

 

[dave_m]

...but I removed the 6520 and it comes to life (without cursor, of course). So I put a "modern" replacement (6821 instead of 6520... I'm sick and tired of old, unreliable MOS ICs...) and now it works like a charm.

Giovi,
Nice to hear from you in sunny Brazil. I am glad you have had success in fixing so many PETs over the years. Years ago did you once fix a PET by replacing all the ICs? If so, I am glad that daver2 has taught you to use his PETTESTv4 firmware diagnostic code. Isn't this a good way to troubleshoot?

I noticed your football team is going to the next round. Good luck to the team.

When you say 'MOS ICs', do you mean the ones from MOS Technology (Commodore) or all NMOS chips in general? I would guess that the 6821 is also NMOS from the 1980's.
-dave_m

 

[giobbi]

Giovi,
Nice to hear from you in sunny Brazil. I am glad you have had success in fixing so many PETs over the years. Years ago did you once fix a PET by replacing all the ICs? If so, I am glad that daver2 has taught you to use his PETTESTv4 firmware diagnostic code. Isn't this a good way to troubleshoot?

Hi Dave!
nice to read you again!

Yep, you're totally right. When I started to fix that PET I had no idea about what to do, and how; it was about the year 2000 or 2001, I guess, and I didn't find any info or help on the web at that time (maybe my fault, I don't know). When about 12 years later I found this forum was a giant leap in many aspects. I'm still in trouble when I have to fix a computer, but I got a lot of knowledge, at least about what NOT to do, LOL --- BTW it still works fine!

I noticed your football team is going to the next round. Good luck to the team.

Thank you! To be honest, my football team is Italy... but nowadays is better to cheer for Brazil LOL

When you say 'MOS ICs', do you mean the ones from MOS Technology (Commodore) or all NMOS chips in general? I would guess that the 6821 is also NMOS from the 1980's.

Yes, I mean MOS Technology. I have to say that often the faulty IC in a Commodore computer is labeled MOS, or at least it seems to me...
The 6821 I used is labeled Motorola, and the date stamp says 1822.

-- Giovi

 

[dave_m]

The 6821 I used is labeled Motorola, and the date stamp says 1822.

Giovi,
The date code indicates it was made in the 22nd week of 2018. That can not be. Motorola has not made the part for many many years. You may have a Chinese copy. But at least it works, many do not.
Consider the Western Design Center replacement part for the PIA. The W65C21N is a CMOS part that is directly compatible with the NMOS part. There is also a 65C22N VIA part. Just make sure you get the NMOS compatible part not the 65C21S part. See this page for the differences:

https://wdc65xx.com/integrated-circuit

 

[giobbi]

The date code indicates it was made in the 22nd week of 2018. That can not be. Motorola has not made the part for many many years. You may have a Chinese copy. But at least it works, many do not.

I strongly suspected it, but the IC works, so I'm happy, as you told, it could be a fake. It isn't, great!

Consider the Western Design Center replacement part for the PIA. The W65C21N is a CMOS part that is directly compatible with the NMOS part. There is also a 65C22N VIA part. Just make sure you get the NMOS compatible part not the 65C21S part. See this page for the differences:

https://wdc65xx.com/integrated-circuit

I have few WDC spares too (of course, they could be a Chinese copy too, of course). But I didn't test a 6821 as 6520 replacement and so, out of curiosity, I did a try. And it worked!
Thanks for the link, I added to my "read before you buy" list ;-)