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CBM4032 problem with keyboard

J

jjpou

Member
Joined
Aug 7, 2011
Messages
19
Hi,

I own a defect cbm4032 since 3 years and failed to repair it. the cbm did never show something on the screen nor play the music "shriiiink shriiiink shriiiink".

i did a lot of basic electrical tests, i bought a scope to verify the 6502 activity was ok and it was, but all my attempts to find the failure failed :(
(i am not skilled at all in electronic). i did verify all the eproms (hopefully socketed) in inserting them in my 8032 and a prg compared them, the 4 eproms were ok)... i forgot the 4032 in its closet.

Reading vintage computer since a few months, enjoying the successfull repairs of some guys here, or "in progress" repair ; i recently gave another try to repair the 4032. I did un-sold all the RAM 4116 (all the UAx in fact) and solded sockets. I bought all the replacement chips as new (the 4116 come from Unicorn Electronics, not found them in my country France :()

Afer re-populating the sockets, the result was succesfull and immediate :) ; the 4032 did play the famous music, i was so happy but very surprised also !

http://jpoudata.free.fr/web/IMG_8454.JPG

the amount of memory in the pic above is only equal to 8x 4116 rams but i added the last 8s and the amount is 32743 now:D

here's a pic of the line UAx socketed

http://jpoudata.free.fr/web/IMG_8458.JPG

and the other chips of the motherboard (few are socketed :()

http://jpoudata.free.fr/web/IMG_8459.JPG

I tried to connect the PETDISK and after i did, the screen was black and all my attempts to start up the 4032 failed :( (without Petdisk connected). i thought that my victory has been very short but five minutes later the 4032 did power on successfully :confused:

i connected the PETDISK and load"$",9 has been successfull :D

it still remains one BIG problem. The keyboard doesn't react correctly, few keys are working and work or don't work randomly, i need to push the key during 5 seconds before the character appears, sometimes 2 or 3 characters appear at a time... If a character appears, it is always the good one.

after a lot of patience with the keys i did load and started a PRG from the PetDisk ;) But the 4032 in unusable like that.

I will clean the keyboard and keys as indicated in another topics here, but the problem seems to be elsewhere (chips ?) and i would like your opinion ?

Sorry for my poor english.
 
Congratulations on fixing your PET!

To me, it seems like you only need to carefully clean the bottom of the keys and add conductive paint or pencil lead (graphite) to the rubber bottom to make it 'conductive' again. Old age makes the keypads non-conductive and prevents it from making good electrical contact with gold contacts on the printed circuit board.

Something like this may work well:

http://www.mgchemicals.com/products/8339.html
 
Yes, well done - you have made your machine come alive again!
I can't help you with the keyboard problems, but I think you will fix that too.
 
Congratulations! Your PET lives again!

Has anyone tried the rubber rejuvenator product that Dave posted the link to?
I've had similar problems with some of my PET keyboards, and while they have improved with the graphite pencil treatment, they are still a bit flaky.
I might try the rubber rejuvenator to see how well it works.
 
very interesting, i need to buy one !

unfortunately my victory has been short... The 4032 was starting up randomly and now doesn't start anymore.
I was testing the removed keyboard (but connected), testing all the keys of the board with a working keypad ; the letters were appearing on the screen then it freezes and the 4032 doesn't power on anymore.

A skilled friend says that it's a "dry soldering" , i need to check all the solderings and to continue to replace the chips with a socket and a new chip ;)
 
azog said:
Yes! It works GREAT! My experience: http://www.azog.org/?p=931
Click to expand...

After reading your experience with the Rubber Renue, I think your problem was not wiping the liquid off the contacts.

The way I found works the best with any conductive rubber application is to WIPE the RR on with one end of a q-tip and wipe it off with the other (dry) end of the q-tip. You, basically, want to REMOVE the top layer of conductive rubber.

It's always worked on the applications I've used it for and has brought totally non-functional keyboards back to 100% functionality
 
jjpou said:
A skilled friend says that it's a "dry soldering" , i need to check all the solderings and to continue to replace the chips with a socket and a new chip ;)
Click to expand...

Exactly what are the new symptoms? Blank screen or random screen? Your friend may be right. It may be a dry solder joint or some other intermittent connection at a cable connection, socket, etc.

Work carefully and methodically as you are very close to having a working machine and all the parts are probably working OK. Try not to create new problems by making a mistake like connecting something 'backwards' or shorting out power, etc.

Good luck on the new troubleshooting.
-Dave
 
dave_m said:
Exactly what are the new symptoms? Blank screen or random screen? Your friend may be right. It may be a dry solder joint or some other intermittent connection at a cable connection, socket, etc.
Click to expand...

This afternoon i checked the 4116s, some were not perfectly socketed, and i unsoldered UD6 (1st Eprom), and added a socket to it.

Now the symptoms are, when powering on :
- the screen becomes full of garbage caracters for a second then becomes black
- the 4032 plays the music "shriiink shriiink shriiink"
- the screen remains black.

it happened like that the last 5 times i powered on and the same happens in the 8032 box or the 4032 box (fat 12")

the dry solder joint seems to be solved but still a problem... your opinions are more than welcome :)
 
jjpou said:
Now the symptoms are, when powering on :
- the screen becomes full of garbage caracters for a second then becomes black
- the 4032 plays the music "shriiink shriiink shriiink"
- the screen remains black.
Click to expand...

OK, The PET is trying to work. The video RAM powers up with garbage characters which is normal, and the program in ROM is clearing it, but then the program becomes lost, possible due to a bad ROM connection. I'll check the power up software code to see what chip is involved after the clearing of RAM. If you are familiar with 6502 assembly code, I can post the Initialization code for you to look at.
 
that would be great Mike !
you mean that it's possible to find where the program becomes lost and then the address of the ROM which has a bad connection ?
wow. i wrote some prgs with 6502 assembly code but it was 27 years ago... Not sure to read it again without help ;)
 
dave_m said:
possible due to a bad ROM connection.
Click to expand...

you were right, it was a bad ROM (but the rom itself, not the connection).
Because i own a working cbm8032, i've been able to change each ROM of the 4032 with the corresponding ROM of the 8032.
The 4032's faulty ROM was UD6 (the first one). The 4032 works fine changing only UD6, it seems stable, i wrote a prg and it runs fine and for a long time, fingers crossed :D

http://jpoudata.free.fr/web/IMG_8463.jpg

Thanks for your help,

JJ
 
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