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VIC-20 Issues

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I recently obtained a VIC-20, and I have found that the 2 key does not function at all, and that the 4 key displays the $ when pressed without the shift key. Also it will display 4 when the Commodore key is pressed with it. It also displays other characters at times. All the other keys work fine. I have cleaned the keyboard and that did not help. Swapping out a known good C64 keyboard did not fix the problem as well, and just to check I reseated all the socketed chips which also did not help. I have done some reading, and what I have found seems to suggest that the 6522 chip that controls the keyboard may be failing. Before I replace the chip I thought I would see if there is any other thing I should check/troubleshoot.

Another issue is the RF modulator. It outputs a very poor signal (bad V-hold, H-hold, inaccurate colors, and noisy), but after using it for a bit it has started to get better. I am fairly certain that this is not a fault with the VIC chip because the video quality changes if I hold the RF modulator or change between the channels (sometimes channel 3 is better and sometimes channel 4 is better). Is there any thing I can do about this or should I just find a new modulator?
 

KC9UDX

Space Commander
Joined
Jan 27, 2014
Messages
7,468
Location
Lutenblag
I would swap the 6522 first though if the symptom really is so isolated I might suspect a flaky ROM. The 6522is readily available and easy to swap.

I would start with the modulator by looking for a bad connection or solder joint. It also may have internal adjustments you could try but it may be just bad condensers.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
Thanks. I will look for one of those chips. I hope that the ROM isn't bad. If it turns out to be something up with the ROM which one should I look for?

The RF modulator was an easy fix. There were two adjustments on the inside of it. I adjusted the one that appeared to be a variable resistor, and I was able to make the video appear clean and with the proper colors.
 
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