• Please review our updated Terms and Rules here

Cbm Pet 2001 restoration

Desperado

Veteran Member
Joined
Nov 25, 2017
Messages
6,786
Hello everyone, I'm trying to restore an old Cbm 2001 ... The computer has a crooked frame in some places and has some keys missing. I started taking everything apart and washing the pieces. How can I go about trying to straighten the bent pieces and where can I find the missing frets? Thanks so much to any suggest



ZPfBTNanAAAAAElFTkSuQmCC
 
Springs can be easily had on ebay, replacement aluminum key overlays are also now available on ebay. I suppose you need to dig through the sites that host 3D print projects to see if anyone has made the file to print new stem and keycaps. In the long run that will be your cheapest option. Finding a complete 2001 keyboard online will cost a fortune.
 
Hi guys,
im desperate like an housewife :(
I tryed to turn on this 2001-N Pet but doesn't works....one voltage regulator ( LM340) is very hot, i measured tension on his pin and I read only 0,2V....
What can i do please?
Thanks so much!
 
Hello again my friend.

You have two possibilities:

1. The LM340 regulator is faulty. Replace it. This, however, is the less likely of the two possibilities.

2. The 5V rail being fed from this regulator has a short circuit on it and the regulator has shutdown to protect itself (and the PET). The most likely fault is a capacitor has gone short circuit (probably an electrolytic or tantalum depending upon what is fitted). Follow the +5V rail from the LM340, disconnect one lead of the capacitors you come across and check for a capacitor short circuit with your multimeter set to measure resistance. If that capacitor is Ok, solder it back in and move on. It is unlikely to be a ceramic disk decoupling capacitor. It could also be a faulty IC.

Sorry, this is a nasty fault to locate - you just have to be patient and methodical.

Dave
 
Hello again my friend.

You have two possibilities:

1. The LM340 regulator is faulty. Replace it. This, however, is the less likely of the two possibilities.

2. The 5V rail being fed from this regulator has a short circuit on it and the regulator has shutdown to protect itself (and the PET). The most likely fault is a capacitor has gone short circuit (probably an electrolytic or tantalum depending upon what is fitted). Follow the +5V rail from the LM340, disconnect one lead of the capacitors you come across and check for a capacitor short circuit with your multimeter set to measure resistance. If that capacitor is Ok, solder it back in and move on. It is unlikely to be a ceramic disk decoupling capacitor. It could also be a faulty IC.

Sorry, this is a nasty fault to locate - you just have to be patient and methodical.

Dave

Hi Daver2!
Ok thanks so much my friend!
 
Update...i removed 7812 voltage reg from the board and i solded B pin on 23V input board s' pin...i measured E voltage reg. pin and i haven't 12V but always 23V! It's normal this? Thanks!
 
Very bad news. If this happened on the PET board before something shorted, you may now have many bad parts. You should trace out which parts are connected to that +5 V output.
Before you replace the regulator, on un-powered board, use ohmmeter to see if short is still there.
 
Hi Dave_m, thanks for your advice!
""Before you replace the regulator, on un-powered board, use ohmmeter to see if short is still there"....for do this must i resold bad voltage regulator and testing if this is in short? Thanks!
 
No, we can assume that one of the capacitors has shorted. So before solder of new regulator, check for shorted part (one of the loads including capacitors). If no short, then solder new regulator.
 
I bought new voltage reg. but i have always 22V input and 22V output (with v. reg out of board and with only input soldered),,, in the others 2 voltage regulators i have 9v in input pin..
 
Where is the 22V coming from? Does not +9 V feed all four of the regulators (pin1 input of voltage regulator)? Are you measuring stray AC without having a proper ground on voltmeter??
 
Update, i have some capacitors in short :(
If i sold voltage reg. without these little capacitors, it works fine!
 
If you have short circuited decoupling capacitors - the output voltage must be closer to 0V than to 22V?

Where is the extra voltage coming from?! If you can find out - patent it and make a fortune :)!

Without the decoupling capacitors, the voltage regulator can become unstable.

Dave
 
Update:
i changed all little capacitors and Cr13 diode, now board works!
I have some software because screen is full of symbols but it's a good first step ;)
I bought also a little 9" b/n TV....fortunately i have same connection pin on the scope ;)
I connected also the 4 wires (Vertical and Horiz. video) and i turned on!
Finally i have screen but something s' wrong....the picture on screen is too little...petter.jpg
Can someone help me please? Thanks!!
 
Last edited:
Congratulations on finding the bad parts. That was not an easy job.

We may need Hugo, Frank and Daver to help adjust the horizontal position, but otherwise it seems OK to me.
-dave_m
 
There us clearly something wrong with the PET video circuitry somewhere - in addition to the monitor size issue.

The first thing would be to measure the ac voltage from the transformer to the video monitor. On my PET these are two thin brown wires from the transformer to the monitor board.

You will also need to measure the dc voltage from the voltage regulator on the monitor board.

This PET of yours seems to have problems with the dc power supplies, so that will be the first place to start.

Do you have a copy of my PETTESTER that you can exchange for the EDIT ROM?

Dave
 
Back
Top