Commodore VIC 20 with issues

[grimm]

I have an early VIC 20 (with the two-prong power connector and gold labels) that is in really good condition. I haven't powered it on in about 8 years, but it fired right up no problems. As far as I know you don't have to worry too much about the power supplies with these models as they are just an AC transformer and the DC conversion happens in the computer. I didn't notice the problem until I opened the computer up and saw that the main large capacitor had leaked and there was corrosion all over the positive lead.

I purchased a recap kit from Console5, with not a bad price and they have the correct axial capacitors. Here is how the capacitor looked like when I opened the case...



It didn't do a lot of damage, this is how it looked after I removed the bad cap...



As I was replacing other capacitors I found three others that has also leaked. They were all located in the video can area of the motherboard. One of them I was able to clean up and replace, the two others have an issue. On both of them (C23 and C24) the negative lead pad on the underside of the motherboard had corroded so much that they just fell off. I was extremely careful when I removed the caps but to no avail.

Here is a picture of the underside with the missing pads. There are no leads that go to these pads on the underside, just on the top of the motherboard.



Now even though these are missing the computer still works, but I'm thinking that it might affect the video quality? Is this the case, does anyone know? I'm also going to have issues putting the new caps in as, on the negative leads I can only solder them from the top. I don't have any plans of replacing the can's lid as I have some heat sinks on the VIC chip to help keep it cool. So I think I can just have the caps sit higher above the PCB so I have some room to solder them? Once I removed them and cleaned up the top pads, they are in ok shape...



Jason

 

[grimm]

Another problem with these early Vic 20s is that the linear 5v regulator runs really hot, hence the very large heat sinks, etc. I have seen images of Vics with distorted and melted cases from the heat. In that case I suspect that the computer must have been running in a hot environment and for a long time. EzSBC has a very cool pin for pin replacement of the 323 can type linear regulator with the same basic shape and through holes.

Original 323...


The new replacement that uses modern electronics...


This should keep this computer running for another 40 years I hope. Here is the state of the motherboard at this point. I have replaced the capacitors except the two in the video can, swapped out the 323 regulator, and added heat sinks to those chips that get hot.



Next I need to re-attach the heat sink for the rectifier and check the key board for issues. I'm not going to replace the rf shield on the bottom of the motherboard or the cap on the video can as they just hold heat in and cause the machine to accelerate it's decline. I will keep these items with the computer in it's box.



Jason

 

[Hutch]

I had a similar experience with leaking caps on both of my 1982 VIC-20s. Some pads under the caps were totally dissolved.
I didn't have any problem with pads on the bottom of the board since the corrosion didn't reach there.

I left some extra lead length on one of the new CAPs and bent the lead to bridge over the pads that were dissolved.
As long as you're connected electrically, you should be fine.
Link: https://youtu.be/w5sTxsx4qgY?t=400
Link: https://myoldcomputers.tumblr.com/post/614938415227650048/vic-20-future-proofing

 

[grimm]

Thanks Hutch, I will do that. It's interesting that the bottom pads on my board were the ones to corrode.

I have looked at the keyboard and just one key was not working, the run/stop key. I took the keyboard apart and cleaned everything and now it works great. These older keyboards are a real pain to deal with, especially with those tiny rubber cups for each key. Next I will solder in the other two caps and then put it all back together.

 

[grimm]

I finally have some time to work on the Vic again. Thanks goes to Larry who pointed me to zimmers.net with the Vic schematics so I was able to track down what those two caps were doing. I used the oldest schematic I could find so I'm hopeful that it's the correct one (the assembly number is 324003). According to the schematics both capacitors (C23 and C24) have nothing to do with the video even though they are in the can. They are used to filter the +5 supply for one of the roms and the Vic chip. The 323 regulator replacement that I put in probably produces cleaner power than the original did, so I'm going to wait to replace them until I am better at it (or someone else does it at some point).

I put everything back together again except the motherboard RF shield and the can top.



This system still has it's original manual, RF converter, box, and packing. I put the RF shield and the can top in the box under the Vic for prosperity.



I also noticed some browning of the box and inserts in places. 1982 is right at the verge of when printing companies were moving to a new process that produced less acid in the paper they were using. I might need to de-acidify the box at some point before it starts to get brittle.

On to the next project, a 32K Tandy TRS-80 COCO 1 also from 1982.

 

[giobbi]

If you want a better video quality and don't mind about to make a small (and easy to revert) mod on your VIC-20, you could upgrade the video output from composite to s-video. It will improve a lot the video quality at the price of one capacitor and one resistor.

The link to the mod page: http://sleepingelephant.com/denial/wiki/index.php?title=S-Video_output

as you can see, it's easy to do and easy to revert in case you want the composite output again.

I modded one of my VIC-20, the one I use for tests, and the video quality is really good and stable if compared with the original composite one.

 

[grimm]

Oooh, thanks giobbi, that is a very interesting mod. It should be compatible with the RetroTink, but would need a new cable I'm assuming? I wouldn't do the mod to this Vic because it's in such good condition and cutting traces would go too far for me. I do have two other Vics that are later than this one (1983 I think), which I wouldn't have an issue doing the mod to. I will have to do another thread on those machines. One is a Canadian Vic which works great, the other has the Eurostyle type keyboard, but is broken (black screen) and has missing keys.

 

[giobbi]

Yes you will need do build another cable, similar to the C=64 one (but with different plug), with Chroma and Luma in two different RCA plugs or an s-video connector, depending on your monitor/TV.

Cutting traces is easy, a sharp knife will do the job. Somebody post a video on youtube too about this mod.

If you have more than one VIC-20, like me, a good idea would be to take the aesthetically worst one and use as "combat vic" for mods, tests, etc.