• Please review our updated Terms and Rules here

Commodore pet 2001-8 with garbage screen

Y

Yanick

New Member
Joined
Jan 16, 2011
Messages
7
Hi,

I just got a new PET 2001 and it shows garbage characters on the screen. There is always a pattern of 250 characters that repeats. The characters won't change is I just power on/off the computer. When I switch them on the video ram area, the characters change. However, there is always a 256 characters pattern.

I have also tried to put some 6550 on top of each other on the video ram side. That also changes the string of characters. At one point, I had one pattern, and a few seconds later, it switched to something else. I moved the chips around and I can't reproduce it :(

I have a 1541 disk drive (that works) and noticed that some of the chip are similar, like 6502, 6522 for example. Can I just try them on the PET, just in case?

This is what I have:

COMPUTER: PET 2001-8 with calculator type keyboard

RAM: 6550 (1578, 1478 or 3177 below)

ROM (in order): 6540-011, 6540-013, 6540-015, 6540-016, 6540-012, 6540-014, 6540-018. 013, 015 and 016 are ceramic and they don't seem to be cracked by just looking at them.

CHAR GEN ROM: 6540-010

PROCESSOR: 6502


On a side note: my computer is also missing screws holding the cassette player and for the cassette player itself. If anybody knows which screws I need, let me know.

I live in Toronto, Canada... if an expert is around, it would be appreciated!!

Thanks!!
 
Last year we had the PET Alive! celebration. Given how many threads about broken computers have shown up lately, perhaps it is time for the PET Revive! event.
 
Mike, I just PM you.

the PET revive event would be a successful event for sure!
If only the part were still available, it would make things a bit easier.

I'll try to do a few things in the next few days and keep you updated of the status.
 
Got your PM; Toronto's the home of a still reasonably active TPUG (Toronto PET Users Group, the second PET users' group to be established in those ancient days) and a few of its wizened old original members like me are still around, so I'm sure we'll be able to find the expertise and maybe even the parts to revive that original PET.
 
carlsson said:
Last year we had the PET Alive! celebration. Given how many threads about broken computers have shown up lately, perhaps it is time for the PET Revive! event.
Click to expand...

Yes, the PET hospital has certainly remained open with no shortage of patients! Kudos to you guys for continuing to help people.

Given all the non-working PETs discussed I'm almost loath to boot mine up again in case it doesn't work and I have to join the casualty list! (-:

Tez
 
Thanks to Mike's generous help, the computer is in a much better shape now.
There is still some work to be done, but I consider it more than 50% repaired!

The 6540-018 was the main culprit for the garbage screen, once replaced, the garbage was gone and replaced with the 'commodore basic' line and free memory.

There were also a few bad 6550, but that's not the end of the world... I can still get 5,119 bytes free.

The keyboard did not work at first, but eventually, more and more keys started working. It may just need a good cleaning. That's my next step.

The tape belt is missing, so I can't test the player. However the motors seems to be running ok when I press play, rev, ffwd and stops when I press stop.

The main problem now is a dual image on the screen. One is in the correct location, but there is another image 136 character later. (3 lines + 16 characters). I attached a screenshot for your information.

PET.jpg
 
Yanick said:
The main problem now is a dual image on the screen. One is in the correct location, but there is another image 136 character later. (3 lines + 16 characters). I attached a screenshot for your information.
Click to expand...

oops, I just realized it's 4 lines + 16 characters, so 176 characters between the two cursors.
 
Actually, probably the way to 'count' is that there are 256 characters from the beginning to the second cursor... thought 176 would be a strange number.

When I had the garbage issue, there was also a difference of 256 characters, so this is not new. I also checked images prior to shipping to me and it was the same, so shipping did not cause this.
 
Yeah, we replaced the socketed chips and found one bad ROM and two bad RAMs (and broke a pin off a third ;-) ), but it looks like there's still a problem in the video memory addressing somewhere. I didn't have any tools or equipment with me so it looks like it may have to come to "the shop" ;-) for further investigation once Yanick has cleaned the KB and played with it a while. (can't do much without a functioning RETURN key ;-) )
 
OK, the keyboard is clean now... the A and 0 still need a hard press, but I'll fix that later.
I was curious about the dual writing on the screen, so I tried the poke 32768,1 and it printed the 'A' both at the top left and at the other place too...

Then I just typed 0123456... and pressed down after each key. The first cursor follows the usual logic, however the second one is a bit strange. It starts near the center, then goes to the top right, then bottom right and eventually on the left side. After 22 characters, I seem to lose both cursors.

Here's a screenshot of my results. Would there be any other video-type tests someone would know?

IMG_0084.jpg
 
I thought I'd update the group...

I fixed the cassette player. Just needed a new belt and cleaning.
 
You must log in or register to reply here.
Back
Top