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Commodore 4032-12 dead screen

A

Arnuph1s

Member
Joined
Sep 24, 2014
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44
Hello everyone.

I have a Pet on the way (4032-12) that powers up with a chirp but displays nothing on screen. Wanted to post early as I am new here and my posts sometimes get stuck in mod limbo.

Would love some help in troubleshooting this classic machine to get it up and running. Assuming it's not something simple like blown fuse, what are the things I should look for when tracking down the issue?

Thanks in advance.

Obviously I will post more info once I get my hands on it (CRT lighting up etc.)
 
Okay, so I now have the unit. It powers up with a chirp and peering into through the slots at the back of the screen I can see the CRT glowing. It's pretty dirty inside so that will be the first thing to attend to.

What things should I began looking at to see why nothing is showing up onscreen?

Thanks in advance.
 
Arnuph1s said:
What things should I began looking at to see why nothing is showing up onscreen?
Click to expand...

Find the board top assembly part number so you can check the correct schematics on Zimmers, and check for the video timing signals, Vertical Drive (60 Hz)and Horizontal Drive (15 KHz). Without the Horizontal signal to switch the high voltage section of the video board, you will not get anything on the screen. If no signals and if your PET uses the 6545 CRT Controller, the 6545 needs to be initialized on power up to generate the screen timing signals. So you will have to see if the 6502 is running in program. Do you have a scope or at least a logic probe?
 
Arnuph1s said:
Okay, so I now have the unit. It powers up with a chirp and peering into through the slots at the back of the screen I can see the CRT glowing. It's pretty dirty inside so that will be the first thing to attend to.

What things should I began looking at to see why nothing is showing up onscreen?

Thanks in advance.
Click to expand...
Chirp is good!

Make sure the video cable is making good contact at both ends.
 
MikeS said:
Chirp is good!
Click to expand...

You are right. Hopefully that means the 6502 is running and the 6545 is being initialized. However that would mean the 6545 is bad if OP gets no vertical or horizontal signals? Or as you say a bad connection. Let's hope for bad connection. :)
-Dave
 
Thank you for the helpful suggestions. I will clean it all up and check contacts/board # and so forth and report back. I don't personally have a logic probe/scope yet but worst case scenario is that I will either obtain one or the other or locate a local source who has access to them. I agree the chirp is promising.

Will probably be busy dropping by Amiwest this weekend and hopefully scoring an Amiga but will be devoting some time later in the week to the Pet since my TRS-80s are now running happily and my new acquired SX-64 seems to be working fine (apart from sticky keys).
Thanks again for responding, much appreciated.
 
I had an 8296 that chirped on startup with no display and the 6545 had gone in that one like the lads above have said, it could be that.
Unicorn electronics (in the USA) were a good supply for my replacements.

Regarding the SX-64 keyboard problems, mine was very unresponsive. After I stripped it down, being very careful with separating the membrane. Cleaned the contact pads with isopropyl alcohol and an eraser and it worked fine!
 
Last edited:
Thanks for the advice on the 6545. I will check that once everything is cleaned up.

Yes I fixed the SX-64 keys last night by cleaning the contacts and then extending a couple of key springs. Works like a charm now.
 
Update: Cleaned everything up and tested all contacts. Still nothing on screen. Repair of this is probably beyond my ability. Any good repair resources stateside that I could ship the board to?
 
Arnuph1s said:
Update: Cleaned everything up and tested all contacts. Still nothing on screen. Repair of this is probably beyond my ability. Any good repair resources stateside that I could ship the board to?
Click to expand...
As Mike said, you get a chirp. It's almost working. Do you have a voltmeter or a logic probe? We can talk you through it.
-Dave
 
I am in NorCal. Sacramento.

No logic probe but I do have a voltmeter and your ever helpful advice(and patience) is much appreciated.
 
Arnuph1s said:
No logic probe but I do have a voltmeter and your ever helpful advice(and patience) is much appreciated.
Click to expand...

If your 4016 PET has a 12" screen, you should have a 6545 CRTC. Use your voltmeter set for DC Volts and see if you get a DC average of 3 Volts at the Horizontal Sync UC2-pin6 or the J7-pin 5 video connector. You can use the bare metal chassis as a ground for the black probe.

If you have about 3 volts there, the CRTC is getting initialized and the screen should be getting high voltage to operate. Next we'll check the Vertical signal and the video data signal.
 
I tried the voltmeter at the J7 connector. From looking at the schematics the connector has the following pinout from left to right 7x54321 the x being the cut pin. Based on this the voltage readings were as follows:
7 - 0
5 - 5.13
4 - 0
3 - 5.12
2-0
1-0

Hope that is of some help.
 
Arnuph1s said:
I tried the voltmeter at the J7 connector.
Click to expand...

Nothing seems to be working. No timing signals may mean the 6545 is bad. However there is no video data either which is independent of the 6545.

Also it appears your DVM reads at least 2.5% high as you shouldn't be seeing anything above 5 Volts. What does it read at VCC? Do you know where pin 14 of the small chips are located?
 
There were some miniscule fluctuating readings at the other pins but nothing constant so i was unable to write the values down. My meter is a cheap pocket thing from Radioshack so it giving elevated values doesn't surprise me. Ideally this board needs to find it's way into the hands of someone with better technical skills. Is there a Pet repair resource here in the US? When I have some more time I will disassemble the screen so I can get at the video board and see what is coming up there.
 
I'd be happy to repair it for you, as well as others here. But, the cost of shipping wouldn't be worth it, IMHO.

PETs are easy and fun to fix. I'm sure you can do it with the great help you can get here, if you're not in a hurry.
 
This is weird because I have 4032 with the same problem, it chirps on startup, but the screen is dead, it shows nothing. The last time I tried my 4032 was about 10 years ago, and it worked. Today, is the first time I tried it since then, and I get this same problem.

Reading through this, I have a chip with a 6545. I also have a J7 connector. With a voltmeter, I got these values.
7 - .02
5 - .32
4 - .02
3 - 5.10
2 - .02
1 - .53

Should I start my own thread or continue on here?
 
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