Weird mod on underside of board

[llopis]

Hello,

I'm new to the world of the VIC-20 (and even C64) but I'm enjoying diving into it and learning all I can about it.

I recently acquired my first-ever VIC-20. It was completely filthy, but that's easily fixable.

The computer starts up fine but the video was completely gray. I was able to do some searches and learned I could probably fix it tweaking the C48 potentiometer. Indeed, that fixed it right up.

The board itself is a revision D PAL.

Everything else seems to work fine and I was able to load some games, but I'm not able to get any video with the composite cable (the cable was tested on the C64 and the people I bought it from claim it works on the V-20 as well). The output is completely black. No noise or anything.

EDIT: Cable was not hooked up properly Ignore that. Ooops.

Another question: I noticed some ugly-looking modifications in the underside of the board.

They are under the box area (which I'm guessing it's some the video generation):

Any idea what that is? Is it a patch from the factory or is that a mod someone did afterwards? I looks pretty darn ugly!

Thanks!

[llopis]

Actually, never mind. I tried it again with the C64 and I wasn't seeing any video either. It turns out the cable connection had moved and it wasn't passing the signal to the TV correctly As soon as I fixed it, it worked on the VIC-20 as well.

The question about the botched job on the underside of the board still remains though. Is that normal, or is it some weird mod someone made?

[norm8332]

How's the picture output? Is is clear? Do the colors bleed much? A guess would be that someone attempted to improve the video quality because the CR (cost reduced) VIC-20 (the one you have) is known for having a lesser picture quality than the earlier VIC-20 design because it uses a simpler less accurate circuit for the video output. Just a guess without comparing it to the schematics...

[llopis]

Oh interesting! I'll look around for PAL video mods and see if any of them match what I have once I get oriented around the schematic.
The image quality is not that great. Definitely worse than my C64 with the same cable. Does an un-modded CR VIC-20 have more ghosting than that?

For comparison, here's the video of my C64 with the same cable and TV:

[mrr19121970]

Does an un-modded CR VIC-20 have more ghosting than that?

Yes, try yellow or green text.

[highinfidelity]

IMHO that's a pretty good display for a VIC20. I don't think I've ever seen a better screen on a real CRT television.

[DarwinNE]

If it can be useful, here is a picture of my PAL VIC-20, modified for S-VIDEO output displayed on a Sony PVM CRT monitor

[Floopy]

For comparison, here's the video of my C64 with the same cable and TV:

I don't think it's bad. Looks almost better than mine, although I am using an RF modulator as the small zenith doesn't have composite.

[llopis]

By the way, since I'm working on this board, I wanted to resurrect this thread again.

I compared the board modifications to the CR schematics and this is what I came up with:

I get the part of moving one end of C13 to the other side of the adjustable resistance since that's closer to how the non-CR version of the circuit works.

But what is the madness around the input lock signal into the VIC??? It seems extensive enough that this must be some kind of published mod. Any thoughts?