C64 video problems

[docred]

Hi all,

This is a frustrating situation for me, lol...here are the details, perhaps someone has some thoughts on it.

- 3 commodore monitors (2x1702, 1x1084s) all verified working on a C128 and a Vic-20 as well as a 64C

- 1 working C64C (the while revision) tested on the monitors without problems (8 pin video)

- 5 (yes 5...sigh) C64s that power up, but will not display (or even flicker) on any of said monitors, using same cable and power supply.

- All connections are being made using 8 pin DIN to RCA (except the Vic-20, which is composite through the front 1702 jack of course)

This equipment has all been in good tempurature storage in the basement for a couple years. I broke it out to test a system to give to another enthusiast. Suddenly, I'm finding things not working. I understand the occasional failure, these old troopers are many years old, but 5 of them? 4 are original gray/brown revisions, one is a 64C. I have tested two of them on a tv with the RF output - no go. My working 64C performs fine on the same TV RF hookup.

So...is this the result of a bad power supply or something I may have tested with these in the past, and not realized, is it just age catching up with them, or....? Power LED comes on, and I haven't dug into the guts with the multimeter yet to see how far power is getting, but I thought I would see if anyone had any thoughts. I'm hoping this could be a common problem with a reasonable solution (replacing the vid chip or some such?). Depressing to suddenly realize my backups/spares don't seem to be such good backups...

Thanks in advance for any advice anyone may have.

 

[carlsson]

The power supply is compatible, so you should be able to use the one from your good C64C and test the others. Most likely you have internal faults inside the computers. The breadbox C64 is known for its PLA chip breaking, but it sounds like really bad luck if four out of four have broken down.

Ray Carlsen is a bit of an authority regarding what chips can cause errors. You can start here to check symptoms and causes:
http://personalpages.tds.net/~rcarlsen/cbm.html

 

[docred]

Thanks Anders...yes, I couldn't help thinking it was terrible luck, regardless of how old the equipment is. I've actually used the same ps to test them all (a known good supply), so I know it isn't it. I checked and rechecked my pinouts (thinking of the old 5 to 8 pin differences, wondering if there were two 8 pin configurations or something) to no avail. Thanks for the link as well - I'll check that out and see if I can discover just what has happened.

 

[Pete Rittwage]

That is bizarre that they don't even flicker- you should get "something" unless there is something really bad wrong with all of them, like missing video chips.

The internal fuses could be blown on them. That will cause nothing at all to happen when power is applied.