VIC-20 with shaky picture, distorted sound etc.

jdxpolygon · Post by **jdxpolygon** » Sat Mar 07, 2009 1:17 pm

Hi friends,

I obtained a VIC-20 from someone at my work a while back (or a VC-20, depending on whether you believe the top or bottom of the machine

). It basically works, but the TV picture from the external RF modulator varies in quality, and almost any movement of the wire itself or touching the computer creates little or large distortions on the screen. Also, the sound output seems to have problems. When the machine is first switched on, the sound is a little rough, but after being on a few minutes, becomes wildly distorted. It also seems sound channel 3 is dead, I'm only getting 1, 2 and the noise channels. Any ideas what might be done to improve things, that don't involve major repair or replacements?

I've just finished work on a VIC-20 game, which I developed using an emulator, and I wanted to test it on a real machine. The main issue with my VIC-20 is the sound, I don't know whether the sound is saturating on my VIC because it's broken, or if it would happen on any VIC to some extent? Is the sound very clear on a fully functioning VIC-20, or do you get distortion if you have all the voices at full volume and low frequencies?

Thanks

J

shem · Post by **shem** » Sat Mar 07, 2009 1:37 pm

It would help to know where in the world you are
and whether it is a NTSC or PAL system you are using

Vic20-Ian · Post by **Vic20-Ian** » Sat Mar 07, 2009 1:44 pm

you could try some gentle manipulation of the pots on the modulator (some are accessible under the label).

Best bet would be to buy or make a scart adaptor from Ebay and cut the RF out of the loop and test the sound channels individually in basic.

jdxpolygon · Post by **jdxpolygon** » Sat Mar 07, 2009 1:48 pm

shem wrote:It would help to know where in the world you are
and whether it is a NTSC or PAL system you are using

hi Shem, I'm in the UK and it's a UK PAL machine, at least thats what I've been told. The VC-20 on the top label made me think it was German.

Pedro Lambrini · Post by **Pedro Lambrini** » Sat Mar 07, 2009 2:02 pm

If it says VC 20 then it's a German machine but it's still PAL. Ian's idea of the SCART is advisable IMO. That way if there is any problem with the RF output at any point it will be totally bypassed.

The RF outputs on my Vics is atrocious (and inconsistent!) but using the SCART makes for a gloriously clear picture and sound.

Bacon · Post by **Bacon** » Sun Mar 08, 2009 2:19 am

I second the suggestion to bypass the RF modulator. No need to use that crap in this day and age when all TVs have direct video input.

But the missing channel implies to me that the VIC chip may be faulty. If so, the only way to make it work is to get a new VIC chip.

jdxpolygon · Post by **jdxpolygon** » Thu Mar 12, 2009 4:20 am

Bacon wrote:I second the suggestion to bypass the RF modulator. No need to use that crap in this day and age when all TVs have direct video input.

But the missing channel implies to me that the VIC chip may be faulty. If so, the only way to make it work is to get a new VIC chip.

I presume I'd need some kind of custom cable to go straight to the composite inputs on my TV? Is it by any chance the same one I'd need for the C64?

And is getting a new VIC chip a realistic prospect these days? Or would I be as well getting a new VIC...

carlsson · Post by **carlsson** » Thu Mar 12, 2009 4:58 am

Yes and no. You can get/make a composite video cable that works both on VIC-20 and C64. Many of the cheaper cables you'll find on eBay are of this variety. However the C64 natively has S-Video output and 8 pin DIN connector. A such cable will not be useful on the VIC-20 unless you make internal modifications (see separate thread) to get S-Video out of the VIC too.

As for getting spare VIC-I chips: it probably is hard, but not totally impossible to get one in case you have diagnosed the chip itself to be faulty. Regarding distortion: yes, the VIC chip causes a lot of distortion if you play more than ~2 sound channels simultaneously at maximum volume. In my music player, I never use a higher volume setting than 7 out of 15 and despite that I get slight distortion from playing all four channels. However I don't think even volume level 1 will get rid of it all. It may also vary from VIC to VIC.

Bacon · Post by **Bacon** » Thu Mar 12, 2009 5:00 am

jdxpolygon wrote: I presume I'd need some kind of custom cable to go straight to the composite inputs on my TV? Is it by any chance the same one I'd need for the C64?

Yes, the same cable will work on both the C64 and the VIC-20, provided it's the one with a 5-pin DIN connector at the computer end. There are 8-pin DIN cables for the C64 that provide Y/C (s-video) output. Those won't work with the VIC-20 unless you do some serious modification inside the VIC-20.

And is getting a new VIC chip a realistic prospect these days? Or would I be as well getting a new VIC...

My advice would be to get a new VIC-20, check that it works, and swap the VIC chips to see if you get the same fault with the "old" chip in the "new" VIC-20. If that's the case, keep using one of the computers and keep the other one for spare parts. You never know when you might need another spare part (keyboard, 6522 VIAs, 6502 CPU, etc.).

Bacon · Post by **Bacon** » Thu Mar 12, 2009 5:03 am

Is there an echo in here? ...in here? ...in here?

jdxpolygon · Post by **jdxpolygon** » Thu Jun 18, 2009 9:24 am

I have some new information on this. I opened my VIC and found that there's a little brown capacitor soldered under the main board - it seemed to be the only component soldered to that side of the board, which makes me think it was a repair or modification? In any case, due to there not being much space between the board and the bottom of the case, it was bent down quite close to the board, and one of it's legs(?) looked like it was coming into contact with another piece of soldering, which I imagine would create a short circuit. I tried to re-bend it in such a way that it wouldn't make contact, and the VIC seemed a little better when I switched it back on (although not perfect). Just curious to see if anyone knows, is this component supposed to be there?

J

matsondawson · Post by **matsondawson** » Thu Jun 18, 2009 3:31 pm

It's a standard capacitor, I think it's part of the clock/crystal mechinism. I noticed it when I did my svideo mod, all pal vics I've seen have it, which does not match the revision N schematic that I have.

English Invader · Post by **English Invader** » Wed Jun 24, 2009 7:29 am

I've just bought a VIC that powers up okay but only shows a black screen. I can rule out the A/V lead because it works well enough with my other VIC-20s. Is this problem likely to be related to the VIC chip?

I'd like to repair this VIC because it's in immaculate condition (apart from this one defect). I'm also reluctant to remove parts from my working but less well-preserved VICs. Where is the best place to source individual parts?

6502dude · Post by **6502dude** » Wed Jun 24, 2009 7:36 am

Try swapping 6560 / 6561 chip from known working Vic-20 to determine if VIC chip is faulty (I generally find this most common cause for units with black screen).

carlsson · Post by **carlsson** » Wed Jun 24, 2009 7:38 am

If the two VIC-20's are of the same model (power connector etc), you could simply move the motherboard from the working unit to the good looking one. It will break the relationship between serial number and motherboard revision though.

The canonical list of faults would be Ray Carlsen's document, although perhaps there are other issues that can happen not mentioned in his list.

http://personalpages.tds.net/~rcarlsen/cbm/vic20.txt