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Capt. 2110
September 10th, 2016, 04:28 PM
I'm repairing a friends VIC 20, and I replaced the 2200Uf capacitor, which was unstable, and it still doesn't work. I think I narrowed it down to either the VIC(6560), or the ROM(901486-06). Any suggestions?

giobbi
September 10th, 2016, 05:14 PM
take a look here:

http://personalpages.tds.net/~rcarlsen/cbm/vic20/vic20.txt >> keep in mind this is a list of the most common causes, but not all of them.

Assuming that "no video" means a black screen (video signal present), I have to say the black screen is the most common symptom, and the worst to fix: unfortunately Almost all ICs on the board are responsible for that.

In my experience, Kernal ROM (should be the one on the left of the 6502 cpu) is the most prone to failure. Other ROMs are quite "fragile" too.

Also the VIC chip (6560 ntsc, 6561 pal) uses to fail, but it's more affordable than ROMs.

KC9UDX
September 10th, 2016, 05:39 PM
According to that, my VIC20 shouldn't exist, and I thought it was the most common type. It has the newer DIN power connector but only uses 9VAC. It has the 5VDC supply internal to the VIC20. The original power supply is the smaller kind, but has a factory DIN plug on it.

gertk
September 11th, 2016, 01:11 AM
According to that, my VIC20 shouldn't exist, and I thought it was the most common type. It has the newer DIN power connector but only uses 9VAC. It has the 5VDC supply internal to the VIC20. The original power supply is the smaller kind, but has a factory DIN plug on it.

How many pins are there on the DIN plug ? The types of VIC20/VC20 I had in repair have either the DIN plug (and use 5V DC and 9V AC) or the old style 2 pin plug (using only 9V AC).

If one of the ROM's has failed you can modify a programmed EPROM to fit or use something like the CY7C264 but you need to program it in a special way because of the swapped pins for A10, A11 and A12. It is 24 pins though and fits perfectly.

http://commodore.hcc.nl/forum/2/149600

Note: forum is in Dutch but with pictures :-)

KC9UDX
September 11th, 2016, 03:36 AM
Beats me. 5, I think. It interchanges with a C64 power supply, but a C64 won't work with the VIC power supply because there's no 5V. That's how I discovered that the VIC had an internal power supply.

gertk
September 11th, 2016, 05:13 AM
Beats me. 5, I think. It interchanges with a C64 power supply, but a C64 won't work with the VIC power supply because there's no 5V. That's how I discovered that the VIC had an internal power supply.

Hmm, strange... Have you tried the VIC with a C64 power supply ?
Can you make some photo's of the mainboard ?

giobbi
September 11th, 2016, 05:14 AM
All of my VIC-20 (PAL version) have the 7 pin DIN plug. The power supply is interchangeable with C=64.
I also have a VIC-20 USA model, with the 2 pin plug.

To replace ROM, I use an ATMEL flash memory and some adapters I bought many years ago from Nicholas Welte.

KC9UDX
September 11th, 2016, 09:22 AM
Hmm, strange... Have you tried the VIC with a C64 power supply ?
Can you make some photo's of the mainboard ?

I'm pretty sure it's running with a C64 power supply now. If I get an opportunity, I'll check. And, I sure will take pictures. I know that I have in the past, but naturally can't find them.

The keyboard is odd, too. I think we discussed that here, somewhere. If I recall correctly, the font on the keys is the same as the PET, but not bolded as the PET key font is.

Capt. 2110
September 14th, 2016, 09:00 AM
Well, I picked up another of his broken VIC 20s, and swapped the VIC chip, and lo and behold, it worked.


Kind of.
The colors are very off, and I can't check the ROMs, sine the one I grabbed didn't have socketed ROMs. What could be the issue? Is it my monitor, or is something else bad?

Also, what's the best way to keep the VIC chip running?

gertk
September 14th, 2016, 09:21 AM
From the Wiki:


VIC-20s went through several variations in their 3-1/2 years of production. First-year models (1981) had a PET-style keyboard with a blocky font while most VIC-20s made during 1982 had a slightly different keyboard also shared with early C64s. The rainbow logo VIC-20 was introduced in early 1983 and has the newer C64 keyboard with gray function keys and the Revision B motherboard. It has a similar power supply to the C64 PSU, although the amperage is slightly lower. A C64 "black brick" PSU is compatible with Revision B VIC-20s, however the VIC's PSU is not recommended on a C64 if any external devices such as cartridges or user port accessories are installed as it will overdraw the available power. Older Revision A VIC-20s cannot use a C64 PSU or vice versa as their power requirement is too high.

As for keeping the VIC running, if the voltages on the chips are within specs it will live for a long time... Most of the problems I had with VIC20 are ROM problems, the RAM chips are less likely to fail since they are of the static (SRAM) type meaning single voltage and low power consumption.

Ral-Clan
September 14th, 2016, 11:22 AM
Well, I picked up another of his broken VIC 20s, and swapped the VIC chip, and lo and behold, it worked.


Kind of.
The colors are very off, and I can't check the ROMs, sine the one I grabbed didn't have socketed ROMs. What could be the issue? Is it my monitor, or is something else bad?

Also, what's the best way to keep the VIC chip running?

You should check out the Denial Wiki...it has answers to a lot of your questions:

http://sleepingelephant.com/denial/wiki/index.php?title=Video_signal_adjustments

giobbi
September 14th, 2016, 01:43 PM
Well, I picked up another of his broken VIC 20s, and swapped the VIC chip, and lo and behold, it worked.


Kind of.
The colors are very off, and I can't check the ROMs, sine the one I grabbed didn't have socketed ROMs. What could be the issue? Is it my monitor, or is something else bad?

Also, what's the best way to keep the VIC chip running?

Can you post a picture?

In my experience, and depending of course from kind of issue, video RAM are the first ICs you should to verify in case of "strange" image. You could also try to remove the 4066 (gate) on the right side of video ram (UD1 on my VIC). The computer should boot, but you will got a black and white text on white/cyan background. If nothing changes, maybe this chip is gone.

To keep the VIC working (and ROMs too) you can mount a small heatsink with some silicone thermal grease and super-glue to fix it. I did it, and it run at a considerably lower temperature.
Also, remove the cover from the metallic RF shield and (if present) the aluminum paper shield to improve cooling.