Thin vertical line beside each character?

ulsterfry · Post by **ulsterfry** » Wed Jul 01, 2009 7:34 am

I am looking at a Vic 20 on ebay with the following problem:

"the only issue of not is that there appears to be a thin vertical line next to each letter you type. I am sure i got that by pressing a couple of keys together as you can with Commodore units( i will try to address and sort this out before despatch)."

I have a vague recollection of this occurring on my old Vic years back and as I am thinking of buying one again, I want to know if anyone knows how to fix this or what chip may be at fault.

I realise this may be an obvious one for the older hands here but as I am coming back to 8-bit computing and VICs after a few year's absence I would appreciate some advice. Thanks.

carlsson · Post by **carlsson** » Wed Jul 01, 2009 8:34 am

Some VIC-20's produce a better image than others. Many have vertical stripes along the screen, and the visibility may depend on the colour combination. It seems to have something to do with the additional circuitry next to the VIC chip, although different chips can also produce various image qualities. Recently some people have begun to modify their VIC-20's to output a S-Video compatible signal, which is said to clear up a lot of the noise.

All the above of course is based on that the problem is not with the character generation, so the leftmost pixel on each row always would be enabled. It depends on how wide the line is, if it is in the same colour as the text and so on.

English Invader · Post by **English Invader** » Wed Jul 01, 2009 10:47 am

Funnily enough, the VIC I get the best picture from was bought as untested for £8. I had to spend an extra £10 on a two-pin power supply but it all worked out in the end.

ulsterfry · Post by **ulsterfry** » Wed Jul 01, 2009 3:34 pm

From the ebay seller - if this adds any light to the discussion?

"What happens is the words all look like they all have the sign : to their right and this includes spaces too.
It actually worked fine only a day before this happend. and what made it happen was me pressing mulitple keys at once."

Any further comments very welcome!

ulsterfry · Post by **ulsterfry** » Sat Aug 01, 2009 5:52 pm

I have now received the Vic 20 mentioned above.
I have uploaded a short video (1 min, 4Mb) to my webspace to show the fault previously described.

http://www.ulster-fry.com/vicmovie/movie.mp4

I would welcome any thoughts anyone might have on this?

Looking through other forum entries and other notes I suspect that it is the character rom (UD7 901460-03?) but would appreciate a more informed opinion - thanks in advance for any assistance!

shem · Post by **shem** » Sat Aug 01, 2009 6:30 pm

from what i can see on the video it looks like the fault only accours when using the standard vic 20 characters so i would guess that perhaps it is a problem with the character rom 901460 chip or some control logic around it

i doubt its the vic chip or ram my 1st guess would be the char rom itself
should be easy to fix

matsondawson · Post by **matsondawson** » Sat Aug 01, 2009 6:35 pm

I'd say it's a dodgy character rom for sure.

If it were the VIC, all chars would be wrong.
If it were a short I'd expect all chars to be wrong again.

Time to get out the soldering iron!

shem · Post by **shem** » Sun Aug 02, 2009 9:06 am

Hey ulsterfry
if you stuck I could always have a look at the vic20 for you
Both me and matsondawson beleive that it is the character rom which is the problem here.
Let us know how you get on.

nippur72 · Post by **nippur72** » Sun Aug 02, 2009 11:29 am

I've also noticed that the phantom line is not steady but do flicker, probably meaning it's as simple as a defective contact.

Just to make sure it's the ROM character, try running the following test:

Code: Select all

10 PRINT PEEK(32768)
20 GOTO 10
RUN

on a normal VIC it should give "28", but in your case it should alternate between 28 and 29.

ulsterfry · Post by **ulsterfry** » Sun Aug 02, 2009 2:32 pm

Firstly let me thank you all for your feedback and good intentions - it is a real pleasure to find people willing to spend some time helping someone else for no other reason than mutual interest!

I am glad that others think it may be the character ROM and I'll look around for a donor machine ASAP (or is there another route?) and practice my soldering before attempting the replacement!

To Nippur72 - I have run the program as described and can find no return other than "28". I have run as described for 15 minutes and there has been no variation in this time.

Is there any further check I can do or should I proceed directly to replacing the ROM?

Thanks again in advance for any assistance.

shem · Post by **shem** » Sun Aug 02, 2009 3:09 pm

well i guess if the program returns 28 then it might not be the rom

if you want me to look at the machine i can do that for you however i am in machester postage might be an issue it might be uneconomical unless you really wnat that machine up and running
you might be better getting another vic20 but i just hate to see a faulty machine and if you get another one you are wrinting this one off

matsondawson · Post by **matsondawson** » Sun Aug 02, 2009 5:32 pm

The cpu may be reading fine as timings may be different.
You could try connecting the last bit on the charrom to gnd through a resistor and see if the bit turns off, if it does I'd say it's not a short and that the charrom is broken.

Or try resoldering the char rom pins in case it's a dry joint.

ulsterfry · Post by **ulsterfry** » Sun Aug 02, 2009 5:52 pm

It just looks as if I have no option but to get out the soldering iron then.

OK, but I'll practice on an old ZX Spectrum so that nothing valuable gets damaged!

ulsterfry · Post by **ulsterfry** » Fri Aug 21, 2009 10:45 am

Thanks to help from another member here my Vic is back in action.

I mailed it over to Shem who got it up and running again very quickly and for minimum cost. Having opened up another (older) Vic to see if I could manage the job myself, I found I was unsure of exactly what to do, and a little knowledge being a dangerous thing...

I packed it up and sent it to an expert instead and having replaced the charcter ROM it's on it's way back to me in perfect health. Ready to have its Mega-Cart installed whenever I scrape my pennies together.

Thoroughly recommend Shem's service - if your Vic's in bother, give him a shout!

His profile at http://sleepingelephant.com/ipw-web/bul ... file&u=752

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Thin vertical line beside each character?

Thin vertical line beside each character?

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Vic 20 repaired and back in action!