I checked all of the existing sockets (I mean the original ones from Commodore that's actually hosting an IC); luckily a little part of the soldered trace was accessible by the multimeter probe, so I was able to check all of them. I found the 6502 socket was faulty. For I while I almost hoped in a miracle.... ...almost....

Well, changing the socket I did a little step foreward (or a giant leap backward...): now the garbage screen appears for about 1", then it turns to black (I have to switch the computer on, leave the crt warm a bit, then switch off and on again to see it). So this is the actual position:

- No CPU in the socket: garbage screen.
- CPU in the socket: garbage screen for about 1 sec. then black screen. I've checked two trusted, different 6502 IC to be sure.

It seems the CPU is working in some way now and the system is doing some kind of reset.

Any idea?

Back to basics. Have you measured the 5 volt supply -- recently, I mean?

Do you have access to an oscilloscope or logic probe?

How about a schematic -- can you find one online and share it with us?

Right now you're resetting the CPU by switching the power off and on but it'd be much more convenient and productive to produce the reset by momentarily grounding the Reset pin on the CPU. (But that may be inadvisable -- that's one of the things the schematic will tell us.) I'm sure you would be relieved to stop switching the power all the time!

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

I did it after replaced the old capacitors of the rectifier section with new ones, but I will measure it again, just to be sure...



no Just multimeter.



Here you can find all of schematics. I think it would be easier to take a look this way, since at this page there are also explanations of every page.
http://www.zimmers.net/anonftp/pub/cbm/ ... index.html



Yes, of course, it would be fine to have a reset-button, like my old, beloved Commodore 128

cheers,
Giovi

OK, I still find it difficult to navigate all the files listed on that site. But I did a google search of the site and found this text file. It says "this SCH is valid for the 3008 to 3032. It is just a matter of placing the right 'jumpers' and RAM-ICs."

I have not reproduced the entire text file here, but the author, Ruud Baltissen, also says, "You may copy the schematics for NON-commercial use. I hope you enjoy it. If you use it, just give me at least some credit like "Stolen from Ruud "

The accompanying schematic is http://www.zimmers.net/anonftp/pub/cbm/ ... e/3008.gif The image is rotated 90 degrees, so I'm posting a normal version below.

Assuming this matches your 3032, then you may connect a reset pushbutton from ground to the 10 nf capacitor on pin 2 of the 555 timer IC. BTW, is your multimeter a digital type, or analog (with an actual needle and semi-circular scale)?

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Hi Jeff,

based on my little knowledge, the 3008 share the same pcb with 3016 and 3032, so it should be ok.
I have both digital and analog multimeter, however the multimeter hasn't the ohm part working (it's a 1982 multimeter and it uses that 3v battery, actually out of production). BTW Ruud Baltissen also helped me a couple of days ago with this problem

Well, I did a couple of steps foreward!
- I checked the ROM checksum putting them in my 8032 and now I know they're ok.
- I checked the CPU socket and I discovered it's faulty. So I changed it and now I have that behaviour I had with just one 6502 of mine: the garbage stays for a while then disappear. The CPU is now refreshing the screen.

When at first I wrote on this forum, I wrote on the vintage-computer.com forum too, so now there is a lot of people helping me: you, here, and some nice guys in this other thread:

http://www.vintage-computer.com/vcforum ... 2-quot-CRT

Without your help I probably didn't discovered the faulty socket, so thank you very much for that!

We're approaching the problem from two different ways, and this is quite interesting indeed!

Well, now I only need to find a button on my spare parts cash to make the reset button
will tell you soon!

----EDIT: I put the reset switch; it seems that somebody in the past did the trick, since there was evidence of solder on C68 capacitor. Well, it didn't help. Then screen remains black even with the reset button. At least we have one information more: the reset doesn't makes the garbage screen appear again.

However the reset button made me remember I read something in the past about a monitor switch, so I googled for a while and I found this info: http://newsgroups.derkeiler.com/Archive ... 00431.html
I tried this with this result:
- the garbage stays on the screen until I tap the button, then it turns the display to black screen.
- keeping the button pressed, it doesn't enter in the monitor mode.
maybe this info would be useful for somebody that has enough skill to decipher it...

Giovi

Ok people, after many troubles, I successfully repaired the original 3032 board, thanks to the help of some friends from 6502.org and http://www.vintage-computer.com forums. I tried to fix it for the first time in 2001; I tried many times to get the rid of it without luck; then you people (expecially Dave, Mike and Jeff) helped me a lot and I got it working in 2013, so it's the 12 years fixing
In first it worked only with Basic 4 romset, but later I found a broken trace between 6522 and 6520 that prevent it to boot with Basic 2, edit ROM for graphic keyboard - you can read the whole history at:
http://www.vintage-computer.com/vcforum ... 2-quot-CRT

thanks to you all!

http://www.vintage-computer.com/vcforum ... 1372019188