My VIC-20 broke (videos)

[tsm]

What's wrong? Please tell me it's not the VIC chip!
(When the screen clears and those blinking cursors appear, it's me pressing shift+clr/home)

P1020010
P1020011
P1020012
P1020013
P1020015
P1020017
P1020019

[Vic20-Ian]

As it displays fine at the start it could be some ram in video memory area is broken.

Later videos run with Mole Attack cartridge running does the same.

One trick you can try is running it for a bit and feeling if one of the ram chips is hotter than the others.

[tsm]

Thanks Ian.
I'll add some details.

- When the screen is readable, the amount of free RAM shown is always correct (even with a RAM expansion)
- Blind disk commands work
- A 1541 connected to the serial port resets when the VIC20 is switched on
- The three MOS65245 were socketed, so I replaced them: no change
- It looks like the first 4 chars are repeated all over the screen (but not always)
- When very cold, the computer starts up normally, then it glitches up in a few seconds

If it was a stuck address line, then IMHO the CPU wouldn't run at all. So I really fear the VIC chip itself is at fault. Furthermore, with a RAM expansion the screen RAM is moved but the symptom remains the same.

[joshuadenmark]

You could try some cooling spray on the vic chip to see if the fault dissapear.

Alternative canned air turned upside down will provide cooling needed if you haven't actual cooling spray.

You can order a new vic chip here.

http://sleepingelephant.com/ipw-web/bul ... hilit=6561

[tsm]

It has stabilized. Now the screen is always filled with the first 4 chars.

[Mike]

Most probably a fault inside the VIC, yes.

That VIC is still able to access the character data from the char ROM indicates, that its address lines aren't really stuck, but the address counter for the text screen does not anymore propagate the carry from bit 1 to bit 2, thus looping the first four characters of the screen indefinitely.

At least that fault provides some insight into internal workings of the VIC chip: there is no dedicated adder to provide the start address of the next text line, rather the address counter either is refreshed from a latched value when the text line is not completed, or the latched value is replaced by the running value when a new text line is started.

You should still check though, whether the +5V inside your VIC-20 are within range, and don't have excess ripple (check the latter one with the multimeter set on VAC). An unstable voltage supply can lead to funny displays.

[tsm]

Anyway, I can confirm that it's the VIC, as I tested it in another computer and it does the same. You may want to update the chip vs. symptom chart with this fault. Sometimes it will still produce an almost normal picture for just a split second, then the screen turns to all asterisks.

I wonder what could have caused this. I was using my hacked Super Expander when it happened and now I'm afraid of using it (though I could see that it was still working as expected even after the fault).

[Spirantho]

Did you ever fix your Vic-20? As was mentioned above, I do still have VIC chips in stock if you need one (though I now have somewhat fewer than I had a few weeks ago, resulting in several more working Vics. ).

http://www.mutant-caterpillar.co.uk/sho ... ath=65_105

[Vic20-Ian]

It was Chips for lunch today....

my order from Ian arrived 10am and during my lunch break I replaced 2 Vic chips in my 2 faulty 2 prong Vic's.

Both Vic's are up and running.

The Keyboard on the Pet Keys Vic needs servicing, only the spacebar works.

Swapped the keyboard out and all works fine so it is a keyboard clean next then a repaint if needed.

Thanks you again Ian for the super fast service from http://www.mutant-caterpillar.co.uk/sho ... ath=65_105

I now need some DIL sockets to repair 2 CR boards

[Spirantho]

I'll stick a couple in the post if you want. You should've said. PM me if you still need some,.

[Vic20-Ian]

Arrived today, thank you. That will be this afternoon"s work after a cuppa

[tsm]

Did you ever fix your Vic-20? As was mentioned above, I do still have VIC chips in stock if you need one

I ordered one from you just yesterday! I hadn't noticed your answer in this thread till now, but I knew you had them from another thread.

[Spirantho]

@tsm

One tested VIC chip in the post as of today.

@Vic20-Ian

Did you get your other VICs working?

[Vic20-Ian]

One turned out to be working, it was a loose board.

One was desolated, did socket installed, new chip, still black screen.

I will check the chip in another Vic and let you know.

There are several non vic chip sockets on this Vic so it has been repaired previously.

Any idea what else will cause a black screen if my socket was installed correctly and the Vic chip was good?

[Spirantho]

Usually RAM, I'd say.... could be CPU....