What exactly is causing this problem? (see pic)

[Jeff-20]

Apologies for the lame pictures. I was eager to get this mystery to you guys.



As you can see hi-res makes the screen go into double vision.



Again, what's up with that? The BASIC boot screen seems fine. So do my own type-in programs.



Pac-man is fine. Maybe it's something Tom Griner is doing...



Nope. Fast Eddie is doing it too. What's the difference between Pac-man and Fast Eddie? What exactly could be causing this bizarre video mess?

[Bacon]

Always a good idea to check Ray Carlsen's C= repair articles.

According to his VIC 20 article it's probably one of these:

UB7 6560-101 VIC VIDEO/AUDIO
White or blank screen, garbled or no video, screen full of (or few random)
"garbage" characters. "Blind" disk commands may still work.
Partial failure: Dark or smeary image, loss of color, garbled or no sound,
game paddles or light pen doesn't work.

UB9 7402 (M53202P) OSC MASTER CLOCK OSC
White screen... no RF interference in AM radio (see text). Partial failure
can produce missing color or incorrect colors, slight or severe tearing of
picture or diagonal lines, sounds play at incorrect pitch. Symptoms may only
appear after warmup.

UD8 and UE8 MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC
Blank screen. Partical failure: garbled video or audio. see UB7

[Mike]

Looks like your VIC chip suddenly got problems accessing double-height characters. The upper half seems to be duplicated to the lower half. Try doing a RUN-STOP/RESTORE, and then POKE 36867,25. You should now read:

Code: Select all

$JBH2#
%KCI3#

in the third, and fourth line, instead of 'READY.' - the '#' depicts graphical chars. What result do you get?

[Jeff-20]

Even more unusual! It reads.

Code: Select all

$JBH2#
$JBH2#

Effectively doubling the image as the pictures above show... WTF? Games like Video Vermin and my own BASIC programs are unaffected because they stay out of this mode...

[PaulQ]

These are NTSC versions of these games, right? Want to e-mail me a copy of these games at digitalquirk@yahoo.ca to test out on my Vic?

[PaulQ]

Or just send me an email to say hi. All I ever seem to get is crap from the local freecycle group...

[Jeff-20]

It's not the program. It's the hardware. Carts, tapes, whatever are all equally affected when in "double character" mode. I think all of these games use that mode for some reason (smooth scrolling? Overscan? I have no idea) . They're just making more obvious the hardware malfunction with this particular machine.

[eslapion]

It's not the program. It's the hardware. Carts, tapes, whatever are all equally affected when in "double character" mode. I think all of these games use that mode for some reason (smooth scrolling? Overscan? I have no idea) . They're just making more obvious the hardware malfunction with this particular machine.

Faulty 6560 register... overheated video chip...

Only possible fix: replace 6560.

To prevent this from happening again, use a heat sink on the replacement 6560.

[vicassembly]

I have a VIC with strange video. When I initially turned the unit on all the characters where @. They pretty much changed right before my eyes to the correct characters. When I insert a cartridge, i.e. GORF, all the characters display as @

It appears I have something going wrong with the video.. But how to diagnose?

What does UB7 mean? I notice in the rcarlson page this may be an issue.

I see in this thread something about the 6560 register. (video chip) I have some spare parts around. Should I investigate removing pieces from my spare vice and try them in this one? If so, which ones?

I have NO electronics background and just ordered my first soldering kit.

Any help would be appreciated.

Jonathan

[6502dude]

all the characters display as @

I suspect video ram problem

[vicassembly]

What chips would I need to replace for video ram?