CBM PET 3032 STRANGE BOOT

[Desperado]

Good evening everyone and sorry for the inconvenience, I'm here to just ask for information.. I sold one of my CBM PET 3032 to a boy, before sending it it worked well... Now when the boy turns it on he has this problem: only the writing comes out READY but the Basic writings are not visible. I am attaching the video below... what do you think it could be? Thank you!

 

[robert_sissco]

Not to familiar with the 3032 models, but since it is not even printing the usual header information you would expect to see, maybe the basic and/or kernel ROMS are loose if they were in a socket.

 

[daver2]

It is not powering up correctly - it is missing the Commodore logo and the number of free bytes. This indicates BASIC ROM corruption (or a bad socket if it is in a socket) or the video display height is off and the text I am expecting is actually being displayed off the top of the screen. It could also be the RAM.

The video isn't (otherwise) very informative at all. He needs to video the screen (and keep the camera still) whilst pressing the keys in a sensible and logical order to see what we get on the screen.

It could be the keyboard, it could be the keyboard PIA or the ROM or RAM.

It would seem as though each key is producing multiple (different) characters. But I am not sure due to what I am seeing (or lack of) on the video...

Dave

 

[Hugo Holden]

The video isn't (otherwise) very informative at all. He needs to video the screen (and keep the camera still) whilst pressing the keys in a sensible and logical order to see what we get on the screen.

It reminded me of a lot of new age films & videos where somebody decided it would be better to have the camera wandering around. For people in our demographic it is very annoying and is only useful for inducing vertigo.

 

[Desperado]

Unfortunately this guy can't find the fault...before shipping I'm sure it was working. I asked for the card to be sent back....time to scope??

 

[Desperado]

Good evening guys, i receveid now the board from guys...if i turn on i have sometimes black screen and sometimes scrambled chars...
if i insert pettester i can see correct screen but test is stucked on first Dram Test

 

[daver2]

It is, therefore, most likely that you have a marginal DRAM fault in the lower 16K bank of memory that passes the initial 'simple' page 0 and 1 RAM tests, but fail when this memory is used to store 16-bit pointers and the hardware stack for running the later tests (especially the full DRAM test itself).

Are these RAM chips in sockets or soldered in?

Dave

 

[Desperado]

It is, therefore, most likely that you have a marginal DRAM fault in the lower 16K bank of memory that passes the initial 'simple' page 0 and 1 RAM tests, but fail when this memory is used to store 16-bit pointers and the hardware stack for running the later tests (especially the full DRAM test itself).

Are these RAM chips in sockets or soldered in?

Dave

Hi Dave, unfortunately all ram ics are solded on board!

 

[daver2]

I would try a piggyback test of each DRAM in turn in the lower 16K to see what response you get from the patient.

Dave

 

[Desperado]

Now pet tester is stucked here:

 

[daver2]

It is telling you data bit 7 in the low bank of 16K is suspect. DO NOT change this RAM chip just yet. Reset the PET and see if you get consistent results or not.

How do you know the RAM chip you are using to piggyback is working?

Dave

 

[Desperado]

It is telling you data bit 7 in the low bank of 16K is suspect. DO NOT change this RAM chip just yet. Reset the PET and see if you get consistent results or not.

How do you know the RAM chip you are using to piggyback is working?

Dave

I haven't used piggyback for now Dave!

 

[daver2]

Ok,

So keep resetting the PET and note down any address and data bit that gets reported when the DRAM test successfully runs and detects a valid error.

Dave

 

[Desperado]

Ok,

So keep resetting the PET and note down any address and data bit that gets reported when the DRAM test successfully runs and detects a valid error.

Dave

And this is next fault!
View attachment IMG_20230211_002144.jpg

 

[daver2]

So, what have you surmised from these error reports?

Dave

 

[Desperado]

If this is data bit 7 in the lower bank, can be I2 ic fault?

 

[Desperado]

Now is stucked here with this screen fault

 

[daver2]

Yes I2.

Ignore displays when they 'lock up'. They don't tell you anything usefull...

Dave

 

[Desperado]

Ok..now i changed I2 ic ram but on screen i see always some glitches....

 

[Desperado]

after 3 dram passes test i stucked again...and now when i turn on i have always scrambled chars screen
Reset signal is good...