C64 With Black Screen

[rmzalbar]

Well, the CIA (U1) closest to the keyboard connector handles keyboard matrix decoding. A common test is to swap the two CIA chips to see if the problem changes.

Your second and third pictures actually look normal to me. When you store a color change in a string variable, it represents that entry with a visible character; that mode of entry is activated when you type " and ends when you type a second double quotes mark. You can compare behavior against your other machine or the WinVICE emulator.

Regarding the disk drive, the other CIA (U2) handles IEC serial communication to the disk drive. In the disk drive itself, there is a pair of logic chips that route the command to a 6522 VIA chip (similar to the 6526 CIA on the C64 side.) Try the same command when plugged into the other C64. Don't hot plug or unplug disk drives with the power on, always turn off both devices before you do.

[C64Person]

Interesting... you are definitely right about the color change. I was sure that the other machine didn't do that, but I guess it did.

Didn't notice your update to the above post until now. I will check in the other machine too, and if that doesn't work then I will check with my other drive board. Thanks for the advice about unplugging, good to know.

[C64Person]

Okay, I got the drive to work in the new machine as you described, but I don't have a reliable serial cable, so I will have to get a cable and some disks before it becomes useful. I will try to test it in the old computer if possible, but without the cable it's really difficult.

Now I am getting down to some minor details, but the picture produced by the old machine seems duller than that of the new one, and it's not the VIC because I swapped them and nothing changed. It's not enough to be problematic, just a little annoying when I go from the clear picture of the one to the dull picture of the old C64. If I can fix it, why not, but I'm not too worried about it.

[rmzalbar]

EDIT: you said you swapped the VIC.. so there is the possibility is that the RF modulator just might be a little different from the other one. The luma and chroma come together in that box to mix the composite and RF outputs, and the components there can reduce the quality of the signal. Check out my post on the RF modulator mod that sharpens up the video on the breadbin C64. I did this to both of my 250407 and it make a big difference in video quality. http://www.melon64.com/forum/viewtopic.php?f=12&t=11061

[C64Person]

I modded the RF modulator, and I do like having one cable for both luma and chroma, but I wasn't actually using the output through the modulator to begin with, so I don't really think that it has anything to do with the signal from the A/V port. It could be normal for all I know, but it just doesn't seem to match the color and clarity of the new computer.

[rmzalbar]

It does though. Having the components on the line blunts the waveform for the luma and chroma on all outputs, even if you don't use the RF output. I use the separate luma/chroma at the DIN A/V port and the mod made a big difference there for me.

The newer board is a 250425 and uses a different version of the RF modulator. That is probably the factor which makes the difference between the two. Adrian touches on the differences between them in his video.

[C64Person]

Okay, that makes sense. As I mentioned, it is not really a problem as far as I'm concerned. I'm getting a drive cable and hopefully some disks soon, so I will get those going too!

[rmzalbar]

Awesome! Great job running all the way through this board, and coming out the other side with a READY prompt!

[C64Person]

Thanks, it's been a fun project!

I have been using the C64, but I notice that the VIC-II is getting really hot, and I know that it is normal for the chip to get warm, but this is like burning my finger hot. Is that going to destroy the VIC-II, or damage the computer? I have a small heatsink on it since the thermal tab was broken by the previous owner, but I just want to make sure that I am not going to ruin this computer again.

[rmzalbar]

The 65xx-series VIC-II (breadbin models) definitely needs a heatsink. I'm not sure what the smallest you can get away with is. My board pictured here is using full-length heatsinks obtained from https://www.retroleum.co.uk/c64-repairs-and-mods

I also have one on the CPU, but that's not truly needed. The smaller pair of heatsinks you see on my SID came in a kit originally intended for the VIC-II. All heatsinks are glued on with thermally conductive silicone adhesive, a tube of which comes with the retroleum kits. Since you're not using the top plate of the VIC-II RF shield as part of the heatsink anymore, you should leave it off as it will only trap heat in that little box. I also recommend you leave the top shield off of the motherboard if you still have it for the same reason. My three breadbins used a metallized cardboard shield. I ditch those. I do keep the bottom shields though.

Chips that should have heatsinks:

VIC-II 65xx: ABSOLUTELY MANDATORY Runs on 12V, runs hot, Commodore, uses copper tab to the top shield
PLA: RECOMMENDED High failure rate, run hot (or just use a PLA replacement like PLAnkton)
SID 6581: RECOMMENDED Runs on 12V, runs hot, rare and expensive chip with a high failure rate

CPU and ROM are optional. These both get warm. I usually put a heatsink on CPU if I have any left over, but I don't bother with the ROM (anyway I can easily replace these with eproms if need be.) Not sure if it's a good idea to heatsink the CIA chips. These do fail, but it's thought that the cause is usually ESD or hot-plugging accidents since they are directy connected to external ports, but anything you can do to reduce the thermal swings should prolong the life of any chip.

On the C64C models, the SID, PLA, VIC-II and CPU are now low-power versions that need no heatsinks.