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VIC 20 - white screen - help!

H

herena

Member
Joined
Jul 13, 2013
Messages
15
Location
UK
Hello,

Today my dad did the most wonderful thing and reunited me with all 'my' old computers from in his loft. These little gems haven't seen the light of day for over 20 years....

The Dragon 32 powered up first time and works perfectly, even the magnetic tape games still load and play! The ZX81 I have still to try out... I'll keep you posted, but it has a good vibe about it.

Unfortunately my sweet little Commodore VIC 20 hasn't fared so well in the loft. I have it all connected up but all I'm getting is a white screen. I have read the wonderfully detailed document written by Ray Carlsen, http://personalpages.tds.net/~rcarlsen/cbm/vic20/vic20.txt and I will be working my way through the basic maintenance, and clean up stuff in there, but before I go ripping out chips, I was wondering if anyone had any good ideas for where is the most likely site of the fault?

I've looked around this site and found lots of talk of people buying them off the internet and them not working, whereas I know the provenance of this one, and I know it worked just fine 20 years ago when it went up into the loft.... and it's been kept in the same box as the Dragon and ZX81 so hasn't had any serious temp/humidity/dust/knocks to deal with. So given that time is the only real factor in why it doesn't work... any educated guesses anyone?

To recap:

All parts are original manufacturer, no home grown parts!
It powers up fine
It powers the tape player fine
I get a pure white screen in a black surround
It will not start cartridge games - even launched blind.
I have visually inspected the board; it is clean, there are no cracks, cabling all intact, capacitors 'look' fine, all chips are seated tightly.
Internal fuse is good.

Any help would be much appreciated!

Thanks
 
are you using a black and white tv or monitor? In other word, your white screen with black surround could be a white screen with cyan surround?
If this is the case, the problem could be a bad VIC chip (6560 -ntsc- or 6561 -pal-) or a bad characters ROM (among other problems).

Of course a rom problem is better than a VIC problem, because you can program an eprom. Vic problem is worse than a rom problem because you need a VIC replacement...

Let me know about your TV ( B/W vc Colour) and in case tomorrow I will try to make some tests with my "all-socketed-vic 20-board" so I can give you some more info

-- Giovi
 
Hi,

Thanks for getting back to me, I'm running it through my Samsung wide-screen colour television! (in these days of plasmas and LED's it's fast becoming a vintage model in itself! LOL)

For a couple of seconds immediately after turning it on I get black screen with diagonal moving 'tram-tracks' ( I can't think of a better description) and then it pops up pure white (TBH I think the black surround may be an artefact of the widescreen nature of the telly)

In my heart of hearts I feel it may be the VIC chip, but I'm hoping it isn't and that there is a simpler solution out there!

Thank you for helping me.
 
BTW -

I notice there is a lot of mention on here and elsewhere of older and newer models of VIC 20, mine has got 4 pins to the power supply, so I think that makes it the newer model of the two. I guess that may make a difference if you are diagnosing faults?
 
One other thing I've just found,

If I fire it up and hold shift and press run/stop and then press play on the cassette, when I stop the cassette the cassette deck keep 'whirring' as though it's trying to do something. If I don't hold shift and press run/stop but just press play on the cassette deck, when I stop the cassette, it stops totally.

So it's trying to load from the cassette I think (when I tell it to), it's just that I can't see it trying... it's looking like that dratted VIC chip isn't it.... :(
 
can you post a picture of the white/black screen? This will give us a better idea about the problem.
---> ARE YOU SURE your cable is ok? In other words, are you sure it isn't white/black just because of a wrong/bad/incompatible cable? Take a look to the VIC-20 video connector pinout... I've already seen black screen, white screen, but black and white screen seems to be a strange behavior; I'm wondering if this isn't a white/cyan screen in B/W...

I've already seen a lot of strange behaviors involving the VIC chip, so I wouldn't exclude it from the culprits list... :-/

Tell me one thing: have you any spare parts (i.e. 2114 ram) and an eprom programmer, just in case?
If you haven't some spare parts to check, I think it could be more expensive to fix it than to buy a working one,
expecially if the VIC is burnt; to find a VIC chip normally isn't easy/cheap...

EDIT ----
Are there socketed ICs on the board? I had some *big* troubles due to rusty sockets on a Commodore computer and simply extract and put back ICs into the sockets didn't work, I had to change the sockets.
If/when you will clutching at straws, you could change the sockets with fresh ones (but of course it's a shot in the dark than could pay or not...); at least it's cheap to do...
 
Last edited:
Hi,

The screen is just white, I can get rid of the black surround by fiddling with the aspect ratio settings on the tv. When I first plumbed the VIC up I had the aspect ratio set best for the VIC, but if I let the telly decide it sets itself to widescreen and the black surround disappears. SO really there's just a boring old white screen. No black surround sorry.

DSCF0049.jpgDSCF0050.jpgDSCF0051.jpg

I've just tried to attach some pics of the board, (I don't know if they will work or not) some of the chips are socketed, some are soldered (smaller ones) they all look very clean and shiny, no obvious signs of corrosion.

No I have no spares, yet.... that's why I'm looking for the most obvious culprits before I go ripping bits out, as I'll have to source all replacements before I start. Now if you'd asked the same question 30 years ago that would have been a different story!

cable are the same ones we've always had, they have been stored with everything else, and only ever used with this system. So I have no reason to believe they wouldn't be as good as they ever were.

I can't photograph the screen as my digital camera goes into phase with the screen!
 
ok, you have the CR board, the newer one (the most common, IMO). You can see it has just two big RAM chips instead of many small 6114 chips: they are the two ICs on the lower left corner, close to the three 2114 video ram chips. So you should refer to this model when you look at Ray Carlsen's instructions.

Accordingly to Ray, the white screen could be due to 7402 (UB9) or 6560/6561 vic (6561 PAL in your case, so I can assume you're from Europe like me :-)).

In first you could to the AM radio test, as suggested by Ray or simply piggyback or change the 7402 IC (is the one close to the VIC video chip). Hoping it is the culprit...
If you change it, use a socket instead to solder the replacement on the board.

If the 7402 doesn't work, you should do a couple of tests:

1) extract, clean and put back again the UB7 (6561) in the socket.
2) change the UB7 socket with a fresh one. Believe me, I had a dead computer due to a rusty socket that seemed clean... since you haven't a fresh 6561 to test, you should at least try to exclude every other cause... To find another VIC chip will be hard, but not impossible; you should take a look to eBay on a regular basis, in example.
 
Errmmm.... Houston I think we have (found) a problem.

I'm only guessing but I reckon the inside of the RF modulator shouldn't look like this..... DSCF0052.jpg

So this is an easier fix than chips yes? ;-)
 
I'm currently using the RF modulator, but just bought a cable so I can go composite instead, to see if I can bypass any problem in the RF modulator.
 
Just a doubt: are you totally sure you have a white screen instead of a blank screen?
If I'm right (but it must to be verify) the white screen appears a couple of seconds after the blank (black) screen.

Do this test: simply extract the VIC chip -6561- (caution, don't break or bend any pin!!!) and see if something changes: if it continues with the "white" screen, then what you call "white" is the blank screen. A blank screen can be due to many other factors (almost all ICs can generate it), so you should be sure about it before to point in a direction.

If you have a blank screen, the diagnosis will be harder but it could end in a simpler fix. The hard to find is just the VIC chip, the others are quite to find and if you have an eprom programmer will be easy to replace the ROMs.

In my experience, the most defective was the kernal (the one close to the 6502 cpu), in our case (PAL) labelled 901486-07: I already replaced three on my VICs!
 
The screen is definitely white. Very bright shiny white. As an aside if there was no signal my TV wouldn't locate the channel the VIC is on.

I've now bypassed the RF modulator with an RCA cable, So now I don't get the 'white tramlines on a black background' which I mentioned earlier. Now I just get a black screen and then a steady white screen.

I've had the chips out and cleaned the pins (although they looked fine) and re-seated them, and I am no further on. Still a black screen and then a white screen.

I have a couple of friends on the lookout for a 6561 chip for me, so If one of them comes good I'll let you know.
 
Yes, probably it is a faulty 6561. I have the same behaviour with a faulty 6569 (C64 VIC II).

To find a 6561 will not be easy, but I hope you can find one. Or, keep looking for a good VIC-20 on eBay for a razoable price, sometimes there is one among many with a foolish price. This option will be fine too because you will have a lot of spare parts in case of a future fixing...
 
just won a VIC20 on E-bay which the seller says in fully working.... fun times ahead! (even if it isn't I now have spares!)
 
Fine!
BTW if I was in your shoes, I couldn't resist to fix *my* VIC-20 using the "new" one for spare parts! :-)
Of course I'm not suggesting anything, just telling you what I would do! Crazy and dangerous, maybe, but a bit of madness makes life more hot and spicy :-)
 
haha it's very very tempting yes.... but as I'm not very experienced in this yet maybe I might go as far as swapping the whole board into my case.... A big cheat I know! I have a friend (who does a lot of restoration work on old electronics) who is willing to take #my# VIC away to try to repair it in his own time. TBH he's waiting for the one I got on E-bay to arrive as excited as I am!

I'm not sure but looking at the photo I think the one I've bought is actually better looking than mine - the case doesn't seem as badly yellowed.... it's almost in fact the same colour as the tape player. (which for whatever reason doesn't discolour) I'll see what its like when it turns up... and of course - if it works!
 
herena said:
haha it's very very tempting yes.... but as I'm not very experienced in this yet maybe I might go as far as swapping the whole board into my case.... A big cheat I know! I have a friend (who does a lot of restoration work on old electronics) who is willing to take #my# VIC away to try to repair it in his own time. TBH he's waiting for the one I got on E-bay to arrive as excited as I am!

I'm not sure but looking at the photo I think the one I've bought is actually better looking than mine - the case doesn't seem as badly yellowed.... it's almost in fact the same colour as the tape player. (which for whatever reason doesn't discolour) I'll see what its like when it turns up... and of course - if it works!
Click to expand...

There's nothing wrong with swapping motherboards. I've done it and it's the one piece of successful retro DIY that I've ever done.

One thing you might want to think about is the PSU. The 9-DIN PSUs are quite well known for packing up and blowing C64/VIC-20 chips in the process. The mod in the following thread addresses this problem:
http://www.lemon64.com/forum/viewtopic.php?t=48451&highlight=
 
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