VIC-20 Issues

[Old Computers]

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]

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]

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.