Breadbin Black Screen/Chip compatibility with C64c

[TheGrandPubaa]

Now that I have a working and safe power supply solution, I was able to at least dip my toes into the C64 stuff I picked up last weekend. The C64c powers right up and seems at first glance to work fine - though it's missing the 7 key and the keyboard itself is behaving oddly like the shift/commodore/whatever key is flickering on/off at various times to where i'll start typing letters and end up typing petscii characters. Skimming the internet suggests I could potentially swap in the keyboard from the breadbin into the C64c and it should work, so i've got that option in my back pocket.

 

As for the breadbin C64, it just outputs a black or blank screen. There didn't seem to be any obvious damage to the components on the board, so my first thought is one of the chips is bad(VIC-II or PLA, possibly?). Does anybody know if it is safe to swap chips between the two C64s to try and narrow down the possible fault prior to shopping around for replacement parts?

[TheGrandPubaa]

My apologies for double-posting. As I tried several of the floppy disks that came with the C64 haul, I began to realize there was no sound being generated. If I turned the volume all the way up, I could hear occasional pops of different kinds, but certainly nothing SID-like. Well, it turns out the 6581 in the breadbin C64 works in my C64c(which looks to use the same board type, so no newer SID-II or whatever, the 8580), and so AD&D Secret of the Silver Blades has music and sound effects now. If I want to try and get the breadbin working again, it looks like I will need a new SID at minimum, but I suspect the PLA as being the primary culprit, honestly. I'm sad, because I wanted(want?) to do a dual SID mod, but I suppose that will have to wait for now. Need more toys like a fastloader cart, an SD2IEC, a controller adapter......the wallet squirms just thinking about it. Oh, and most important of all, an S-video cable. This coax nonsense is for the birds.

 

As an aside, the keyboard random keys issue persisted with the BB keyboard, but I reseated the connector several times and positioned things just so, so now it no longer spazzes out to a light blue screen when I jab at the 2 key, so I suspect it's an oxidation issue and the first keyboard probably works fine(just needs a new 7 key and a stalk).

[carlsson]

Your keyboard issues sounds like you'd want to investigate the 6526 CIA chips. There are two of them per computer, the chips are identical but serve different functions so you could swap them to see if the keyboard works better but other functions stop working. Also if you got the same revision/type of motherboard you could probably swap the PLA as well, since you observed you have the same 6581 SID chip.

[TheGrandPubaa]

It looks like most of the chips on the C64c are soldered directly to the motherboard, so i'll have to wait until I can order some sockets before I decide if i'm feeling particularly froggy on that one. I did test the 6567R and the 6567R8 on both machines - on the "C", either chip works fine. On the "BB", the no signal message on the tv disappears but the screen still looks black - maybe I detect a slight faint rolling pattern of some kind, but it's hard to tell. I did find out that the 7701 from the "BB" was bad, but the 8701 that came in the "C" works. I don't have any carts so I can't test whether the kernal rom is bad.