Need help diagnosing video issue with a recently bought VIC

sanchezmanVIC · Post by **sanchezmanVIC** » Fri May 10, 2013 5:59 pm

So I recently acquired a VIC-20. It powers on, but when it plugs into a TV, all that it displays is a white box without borders. I read that an AM radio can be used to detect interference from the computer to detect whether or not the chips inside are working. When I held a radio tuned to about 720 kHz near the computer as it turned on, it gave an audible "Bee boo" over the radio.

Here's a link to a video of the computer turning on with the screen and the radio:
http://www.youtube.com/watch?v=Sr_xexVqClQ

Does anyone know what the problem could be? Is it something as simple as a broken RF modulator, or something more complicated?

Thanks for any help!

HermanVIC · Post by **HermanVIC** » Sun May 12, 2013 6:08 pm

The radio hash is produced by the VIC chip, the noise is a good sign the VIC chip is working.

Regards
Herman

sanchezmanVIC · Post by **sanchezmanVIC** » Sun May 12, 2013 9:50 pm

Are there any simple things I can clean or reseat inside the computer? The inside is very dust free, but not being too familiar with a soldering iron or a multimeter, I don't want to get in over my head while cleaning it.

eslapion · Post by **eslapion** » Wed May 15, 2013 10:06 am

sanchezmanVIC wrote:Are there any simple things I can clean or reseat inside the computer? The inside is very dust free, but not being too familiar with a soldering iron or a multimeter, I don't want to get in over my head while cleaning it.

You don't say what country you're from so its impossible to tell if you have a PAL or NTSC machine.

It seems to me this problem is too complex to solve with only this description of the symptoms.

sanchezmanVIC · Post by **sanchezmanVIC** » Wed May 15, 2013 5:59 pm

eslapion wrote: You don't say what country you're from so its impossible to tell if you have a PAL or NTSC machine.

Sorry about that. I'm in the USA, and it seems that my VIC-20 is NTSC (the back says 117v @60hz). The serial number is P726404 and says "Made in USA" if that helps any.

Taking a look at the VIC chip, it is the 6560 variant. How can I remove it to check that the pins are clean? The metal housing around it prevents me from grasping it lengthwise.

Also, I just realized that the processor says: 6502 B (new line) 3382
Is this a 6502-B processor? Shouldn't it be 6502 A?

Muzz73 · Post by **Muzz73** » Thu May 16, 2013 1:12 pm

Hmm... it couldn't hurt switching out the 6502. It did originally come with a 6502-A, so if it burned out, someone, somewhere may have replaced it with the 6502-B from an 8-bit Atari. They are nearly identical and are even pin compatable, but the 6502-B has a HALT line for the Atari's ANTIC graphics co-processor. I've always thought that it didn't interfere with anything on different systems, but who knows... I could be way off on that!

Mike · Post by **Mike** » Thu May 16, 2013 1:25 pm

In my VIC-20, I also have a MOS 6502B. That's just the variant of the 6502 rated for 3 MHz (bare 6502: 1 MHz, 6502A: 2 MHz). Of course it also runs at lower frequencies like the ~1 MHz of the VIC-20. Commodore just used any CPU that was available.

The variant of the 6502 used in the 8-bit Ataris and featuring the /HALT pin is the 6502C.