VIC-20 was working, now dead unit
Posted: Sat Feb 17, 2018 8:59 pm
Greetings all!
I recently bought an early model (2 pin PSU) VIC-20 from a thrift store. The unit was sold as "untested" but I figured it was worth a gamble. Long story short, I was able to get her up and running. I purchased a PSU and video cable from eBay and was happily playing around with BASIC. Everything seemed to be working fine, just one odd thing was I had to leave the PSU plugged in for a few minutes before I could plug in the VIC and turn it on. If I plugged in the PSU then plugged in the VIC right away it would not power on. When I let the PSU sit plugged in for about five to ten minutes then plug the VIC in, the VIC will start right up
I purchased a copy of Avenger (VIC-1901). I followed my usual procedure of plugging in the PSU then plugging in the VIC a few minutes later. The VIC booted to Avenger and I played a game or two. All of a sudden the VIC shut off and would not turn back on. Switching on the power just resulted in a dead unit and now power LED. I unplugged the VIC and set everything aside.
Tonight I got some time to work on it. I checked the PSU with a multimeter. It is outputting between 9.5 to 10 volts AC. I did a visual inspection of the VIC and the fuse does not appear to be blow and there is no obvious damage not the mainboard. I plugged in the VIC, waited a few minutes and tested pins on both the user port and cassette port. I referred to the VIC-20 user guide and tested pins 5 and 10 on the user port, which should have +5 VAC and +10VAC, but both showed readings around 0.003 VAC. I also tested pin 2 on the cassette port and got similar results.
I've reviewed Ray Carlsen's repair notes and it looks like the rectifier or voltage regulator are likely culprits here. Is there any other testing I can preform to narrow it down further? What sort of repair/replacement options are available? Am I even barking up the right tree at this point?
I'd appreciate any help you all can provide. This is my first Commodore computer and I was looking forward to using it and eventually picking up one of the recent memory expansion/ROM carts.
I recently bought an early model (2 pin PSU) VIC-20 from a thrift store. The unit was sold as "untested" but I figured it was worth a gamble. Long story short, I was able to get her up and running. I purchased a PSU and video cable from eBay and was happily playing around with BASIC. Everything seemed to be working fine, just one odd thing was I had to leave the PSU plugged in for a few minutes before I could plug in the VIC and turn it on. If I plugged in the PSU then plugged in the VIC right away it would not power on. When I let the PSU sit plugged in for about five to ten minutes then plug the VIC in, the VIC will start right up
I purchased a copy of Avenger (VIC-1901). I followed my usual procedure of plugging in the PSU then plugging in the VIC a few minutes later. The VIC booted to Avenger and I played a game or two. All of a sudden the VIC shut off and would not turn back on. Switching on the power just resulted in a dead unit and now power LED. I unplugged the VIC and set everything aside.
Tonight I got some time to work on it. I checked the PSU with a multimeter. It is outputting between 9.5 to 10 volts AC. I did a visual inspection of the VIC and the fuse does not appear to be blow and there is no obvious damage not the mainboard. I plugged in the VIC, waited a few minutes and tested pins on both the user port and cassette port. I referred to the VIC-20 user guide and tested pins 5 and 10 on the user port, which should have +5 VAC and +10VAC, but both showed readings around 0.003 VAC. I also tested pin 2 on the cassette port and got similar results.
I've reviewed Ray Carlsen's repair notes and it looks like the rectifier or voltage regulator are likely culprits here. Is there any other testing I can preform to narrow it down further? What sort of repair/replacement options are available? Am I even barking up the right tree at this point?
I'd appreciate any help you all can provide. This is my first Commodore computer and I was looking forward to using it and eventually picking up one of the recent memory expansion/ROM carts.