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Just broke the PET

P

polishedball

Experienced Member
Joined
Mar 21, 2010
Messages
114
I had wanted to change my pet over to a FAT 40 col since i had a universal board and it originally was a 40.

I missed a few jumpers the first time and now that I have all the jumpers correct and the correct EDIT rom edit-4-40-n-60Hz.901499-01.bin My display is sometimes all "@" symbols but in forty col atleast and most of the time it comes up with garbage and 3 blinking cursors.

Any ideas on where to start?

Thanks
 
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This is how it looks

garbage.jpg
 
Also most of the characters type correct across the rows. but ":" = Z even though Z=Z and "," = L also the number pad puts out all letters.

After re-booting it now seems worse it comes up to this every time and then just quickly flashes to a full screen of garble then back to this. How I wish I had an 11x17 printer to print the schematics, will have to bring them to the kinkos later.
Also the keyboard only produces "@" or Space's when keys are now struck. The cursor does move.

gar2.jpg
 
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I replaced the Static Roms 2114's and the 6545 CRTC. The glitches (flashes)are gone, -Now I have a single blinking cursor on some rows, with still alot of "@" symbols. I can make out the word "ready" just one bad character and kinda the commodore basic but not much of it.

The keyboard give the correct value sometimes less than 10% of the time correct.

This is the current screen, doesn't have an obvious odd/even problem. Also the "@" signs appear instantly at turn on then you can see where the commodore basic pops up later.

gar3.jpg
 
I've seen a similar kind of symptom in a System 80. There was a dry solder in one of the TTLs in video circuitry. If you gently push on various areas of the board and chips while the machine is going does the pattern alter, or disappear?
 
tezza said:
I've seen a similar kind of symptom in a System 80. There was a dry solder in one of the TTLs in video circuitry. If you gently push on various areas of the board and chips while the machine is going does the pattern alter, or disappear?
Click to expand...


I tried that first thinking I had the board out and it was flexed or something. There is no change when pushing on the IC's or jumpers.

I'll how ever try again next time I put the board in, swapping a couple IC's in the video circuit. It wasn't UB3.
 
polishedball said:
After re-booting it now seems worse it comes up to this every time and then just quickly flashes to a full screen of garble then back to this. ...
Also the keyboard only produces "@" or Space's when keys are now struck. The cursor does move.
Click to expand...

It is normal that on power up the screen is filled with garbage characters as the video RAM is scrambled. After about a second during initialization, the screen is cleared and then the the Commodore message is displayed. So some things are working, but I need to give this some thought. I don't like that your keyboard is now acting strange. The keyboard is read by one of the 6520 PIA chips.

There is logic hardware that sends keyboard info to the video memory, logic that continually sends video RAM data serially to the screen, etc. All kinds of mischief may be happening. Keep patient. Since you have a solid 80 by 25 line display, the 6545 CRT chip is probably being initialized properly and is working. We need to study the schematics for a while.
 
I'm curious: what does it look like with one of the video RAM chips removed, and then the other?

And is the blinking cursor gone completely now?
 
MikeS said:
I'm curious: what does it look like with one of the video RAM chips removed, and then the other?

And is the blinking cursor gone completely now?
Click to expand...

The three blinking cursors are gone, now there is just one that shows up depending on where on the line or col it is.
 
dave_m said:
It is normal that on power up the screen is filled with garbage characters as the video RAM is scrambled. After about a second during initialization, the screen is cleared and then the the Commodore message is displayed. So some things are working, but I need to give this some thought. I don't like that your keyboard is now acting strange. The keyboard is read by one of the 6520 PIA chips.

There is logic hardware that sends keyboard info to the video memory, logic that continually sends video RAM data serially to the screen, etc. All kinds of mischief may be happening. Keep patient. Since you have a solid 80 by 25 line display, the 6545 CRT chip is probably being initialized properly and is working. We need to study the schematics for a while.
Click to expand...

Thanks for thinking about this, I assume you mean good 40x25. I did replace the 6545 chip same problem. On power on the screen fills with garbage and then it clears per say to all the "@" signs

thanks again
 
Also if this helps the keyboard is displaying the wrong characters when pressed, but they are the right keys to the cpu? If I type "load" it returns a garbled "PPESQ@P@AY EL@ TAPE"

Also if I then use the cursor after run/stop as the text scrolls up the letters do change there garbled pattern.

I did check the Edit rom and the checksum is valid for it a perfect match to the buffer.
 
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polishedball said:
Also if this helps the keyboard is displaying the wrong characters when pressed, but they are the right keys to the cpu? If I type "load" it returns a garbled "PPESQ@P@AY EL@ TAPE"

Also if I then use the cursor after run/stop as the text scrolls up the letters do change there garbled pattern.
Click to expand...

This is an important clue. It may indicate that the video RAM is bad or the logic chips that read the video RAM and send the data serially to the CRT are misbehaving. Can you perform a POKE 32768, 49 from the keyboard and see if the number "1" pops up on the upper left of the screen?
 
dave_m said:
This is an important clue. It may indicate that the video RAM is bad or the logic chips that read the video RAM and send the data serially to the CRT are misbehaving. Can you perform a POKE 32768, 49 from the keyboard and see if the number "1" pops up on the upper left of the screen?
Click to expand...

Wish I could, but I just swapped the board back in hit the power switch and nothing. I don't have 20v AC or anything even coming onto the board. Not sure yet if the switch failed or what. The fuse is good.

Also I swapped the odd and even static ram chips and know they are good. Tested them in another PET I have.

Will let you know once i get power to the board again.

John
 
MikeS said:
??? The two odd ones shouldn't even be installed, should they?
Click to expand...

Maybe this is my mistake, I left the board jumpers for 32K and only moved all the 80 40 col jumpers. Should it run OK as a 4032?

Also for now, last night I made a major mistake and while swapping in the board, I caused many more problems I shorted some traces on the bottom of the board to ground, a ground lead that was under the board that should have been under a back screw mad contact. The board is now dead, once I get it up an going i'll revive this thread. Thanks everyone so far. I appreciate it.
 
Oops; sorry to hear about your new problem.

32K??? Aren't we talking about video RAM?

I really don't know how well it would work to just move the jumpers and change the ROM but leave the odd video RAM and buffers installed, but I sure wouldn't be surprised if it caused problems.
 
MikeS said:
Oops; sorry to hear about your new problem.

32K??? Aren't we talking about video RAM?

I really don't know how well it would work to just move the jumpers and change the ROM but leave the odd video RAM and buffers installed, but I sure wouldn't be surprised if it caused problems.
Click to expand...

im guessing you found my problem. (hence why I was looking for instructions in the other thread) I did not remove anything just changed jumpers.
 
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polishedball said:
im guessing you found my problem. (hence why I was looking for instructions in the other thread) I did not remove anything just changed jumpers.
Click to expand...

John,
I think what may have happened was that you did not jumper "Detail A" of top assembly properly for 40 columns. See top assembly for the -03 configuration of jumpers 7 & 8.

Also see lower left corner of schematic sheet 8 for jumper 7 & 8 info.

From my look it seems that 40 column mode only uses the two even RAM chips, but having all four 2114 chips should not create a problem if all the jumpers are set properly since the odd chips will never be enabled.

This Commodore control logic is very confusing. Mike please double check when you get a chance.
 
dave_m said:
John,
I think what may have happened was that you did not jumper "Detail A" of top assembly properly for 40 columns. See top assembly for the -03 configuration of jumpers 7 & 8.

Also see lower left corner of schematic sheet 8 for jumper 7 & 8 info.

From my look it seems that 40 column mode only uses the two even RAM chips, but having all four 2114 chips should not create a problem if all the jumpers are set properly since the odd chips will never be enabled.

This Commodore control logic is very confusing. Mike please double check when you get a chance.
Click to expand...

I do have that jumpered, board is still dead but I haven't had time yet to look at it. Just checked and Pin 1 of UC3 is at grd so looks to be correct if I am reading the schematic right. I'll pull that IC and run a vector check on it to see if it is good or failed itself. Thanks so much will update as I continue.
 
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