• Please review our updated Terms and Rules here

Commodore pet 2001-n professional computer start up problem

Junior Ramos

Experienced Member
Joined
May 11, 2010
Messages
63
Hi to all,
I have a commodore PET 2001-N, When power on no showing nothing in the screen.
Then power off and on again and showing garbage, then power off and on again for several time and boot perfect. So I thing there is a problem with voltage, maybe some capacitor. I think this due when the computer boot correct I leave the computer
for some hour then power on and boot fast.

I do not found a service or technical manual in order to troubleshoot the computer.

Any help with this please
Thanks a lot
 
Hi to all,
I have a commodore PET 2001-N, When power on no showing nothing in the screen.
Then power off and on again and showing garbage, then power off and on again for several time and boot perfect. So I thing there is a problem with voltage, maybe some capacitor. I think this due when the computer boot correct I leave the computer
for some hour then power on and boot fast.

Junior,
If I understand you, you are saying that when the computer has been on (warm), it boots OK, but when it is cold, it does not?

This is an unusual problem. Possibly there is a temperature sensitive component or solder connection that works better when things get warm.

Check this link for schematics of various PET models.
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/index.html

An experiment you may wish to try is to issue a "reset" by grounding J4 pin 22 momentarily when the system is cold and then when it is warm to see if the power-on reset timer is an issue. J4 is one of the expansion connectors.
-Dave
 
Your are right,
I will try your suggestion of the reset.
I will let you the findings.
Thanks
 
Hi Sir,
Make a "reset" by grounding J4 pin 22 momentarily when the system is cold and nothing happen, then when system warn, short again pin 22 to ground and the power-on reset timer work (system reset well).

Check all DC voltage Regulator and are ok, except the 12.00 dc (read 11.82 dc) But I think it's ok.
Any others inputs.
Thanks
 
Not as helpful but it can also be bad/cold solder joints. The other common troubleshooting technique is reseating any chips that can. Sometimes a bad connection on an IC will act properly once it's warmed up but not when cold so if there are any socketed ICs I would try gently removing them and putting them back in.
 
Make a "reset" by grounding J4 pin 22 momentarily when the system is cold and nothing happen, then when system warn, short again pin 22 to ground and the power-on reset timer work (system reset well).

This probably means that the power-on reset circuit (555 timer & capacitor) are OK.

Does your system board have some IC chips on sockets? If so, there may be a bit of corrosion. You should push on the opposite ends of the chips to move them a little to re-seat them in their sockets.

If you remove the chips, be careful not to bend the pins. There are removal and insertion tools to make this easier.
-Dave
 
The motherboad was removed and clean and all ICs was removed from socket, cleaned all pins a reinstall, but the problem is present.
Any others hint
Thanks again for your support.
 
Junior,
How long does it take the computer to "warm up". Is it less than a minute or much more before it resets properly?

When you cleaned the board, did you visually inspect it for cold solder (non shinny) joints?

Another idea may be to use some circuit cooler when the board is warm and working to spray small areas to see when it stops reseting properly. That will tell you the area of the problem.

MG403A.jpg
 
The computer take about 1 minute to warm up, I inspect the board under my manifier and everything look ok, Right now don,t have a circuit cooler in order to test it. I try find during this week.
Thank you very much for you help and the others people.
 
Out of curiosity, if it's plugged in for 1 minute before you try to power it on does it turn on ok or is this consistent with taking a minute after it's powered on to work?
 
Yes, something heat-related by the sound of it. I can't really add anything which hasn't been discussed before. A faulty capacitor or a cold solder joint would be my initial hypotheses.

Using circuit cooler to isolate the problem to one part of the board is a good strategy.

I had an issue with an Apple II+ once, where I had the opposite problem. The machine booted when cold but within 15-20 seconds it stopped working. The problem was a faulty capacitor in the timing circuit which failed once it warmed up.

Tez
 
The computer take about 1 minute to warm up, I inspect the board under my manifier and everything look ok, Right now don,t have a circuit cooler in order to test it. I try find during this week.
Thank you very much for you help and the others people.
Ice cube in a double plastic baggie?
 
Hi to all,
I leave the computer plugged and about 6 hours, power on, but nothing happen, Power on and off for several time and starting with garbage, then boot
perfect.
This morning warm the mainboard with a blower just for curious and nothing happen, not boot. Yesterday I inspected a mainboard again and everything is ok
no found any cracked or cold solder.
I will continue working with the computer.
Thanks for everything.
 
Hello,
I found two cold solder not in the mainboard, in the CRT board, The both cold solder correspond to 9V coming from the power supply, This is the reason that the monitor do not show anything, But I need to leave the computer off for about 8 hours, then power on to check if the computer boot properly.

I think there are 2 problem:
1. The monitor no showing nothing due the cold solder in the 9v connector pins. (fixed)
2. The garbage in the screen when power on in the first minute. (today in the night I will power on to see what happen)pending.

I have more than 30 vintage computers in excellent conditions, but my Osborne and my PET has some yellowed, This computer are plastics, but I think the PET was painted in the factory. If I paint professionally matching a color, the computer lost value?

Thanks for your support
 
:) Sounds like you're doing very well and being active in repairing and maintaining them is great! Only to an extremest would the paint matter. Honestly if it matches it's not a big deal. These are vintage, not antique furniture or jewelry where the patina or original finish truly matter. Only if you did something odd and paint it red or something would it maybe get overlooked by a collector. I have an Amiga 3000T from a friend who used to work at Commodore. It was his demo model so it was built up as best it could be. He painted it with this spray on gravel look, but it was because the cases were so heavy everyone joked about them being made out of cement. So in this case, I'm fine with the C= employee joke and paint job ;-)

The garbage is normal, what is supposed to happen "in the blink of an eye" is the CPU initializes, clears the data on the screen/ram, then loads the data from the ROM (I could be out of order) but it's the CPU that's in charge of clearing that data. A similar cold joint for one of those pins could be the culprit as well.

I was looking around for troubleshooting info related to your problem yesterday and found a few folks having similar problems but didn't see a fix. Here is one site on some troubleshooting techniques for the PET they also have some links to other resources there (like the schematics on Bo's (zimmers.net) site).
 
Last edited:
Hi,
Bad news,
After re-solder the cold solder joint, leave the computer for about 8 hours, then when power on again, has same problem.
When power on nothing appears in the screen.
Power off and on again and appears some code see below:
B*
PC IRQ SR AC XR YR SP
.; 0141 E62E B0 FC A9 DC FC
.

When power off and on again after 1 minute the computer boot perfect.
*** COMMODORE BASIC ***
31743 BYTES FREE
READY.

I don't know what is the next step to follow.
Thanks
 
Hi,
When power on nothing appears in the screen.
Power off and on again and appears some code see below:
B*
PC IRQ SR AC XR YR SP
.; 0141 E62E B0 FC A9 DC FC
.

Junior,
We have progress and some clues!

Possibly the CRT solder joints were not the problem, but when the system was cold you got into the machine languge monitor program. This is what the computer tries to do if there is a problem. The B* message means it got to the monitor program by way of a "Break instruction". So it seems your PET was trying to fetch an instruction but saw a 00 hex instead of the instruction it wanted. This could mean a flaky 6502 CPU or a flaky ROM chip. Let's all think about next steps.

La estancia valerosa mi amigo y nosotros conseguirá la computadora que trabaja perfectamente.
-Dave
 
Sorry,
But I don't have programmer to read the ROM.
Yes, the ROM is in socket.
Thanks
 
Last edited:
Back
Top