Commodore 64 - Orange screen problem

Discussion in 'Computer Gaming Forum' started by gs37, Nov 12, 2014.

  1. gs37

    gs37 Robust Member

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    I recently picked up a C64 at a thrift store. It seemed to be in good condition, had the box and manual and everything. I got it home, powered it up, and I was met with just an orange screen.

    Looking online I see that one of the major problems is the epoxy-filled power brick. Testing my pins, I determined that the 5vDC pins were fine. But the 9vAC pins were only 1vAC. I have replaced the failed power brick with a 5vDC 2A transformer going to pins 2 and 5, and a 9vAC 1A transformer going to pins 6 and 7. I have tested the pins on the voltage regulators while its on and I get 12vDC and 5vDC as expected. Fuse is OK.

    I see no burst caps or obvious damage to the board. It looks like it was well taken care of until the PSU broke. That's probably when they gave it to the thrift shop. I would really appreciate some advice, this is my first C64 and I'd love to get it working.

    More info: I am connecting to an old (known good) TV on channel 3 via coax. I am using RadioShack part number 2780476 to achieve this.

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    Last edited: Nov 12, 2014
  2. retro

    retro Resigned from mod duty 15 March 2018

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  3. gs37

    gs37 Robust Member

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    Thanks for the tips! So I don't want to buy a replacement PSU for a machine that may be done for, as those are kinda pricey. I believe the PSU I built for it is working well. Pins 6&7 output 9vAC at 1 Amp. Pins 2&5 output 5vDC at 2 Amps.
    Furthermore, the 12v voltage regulator outputs 12.06 volts. The 5v regulator outputs 4.96 volts. So I believe the system has good power.

    I think the problem is either 74LS629 or the VIC. The pins on 74LS629 seem to be a bit tarnished, does that indicate it's bad? Where is the best place to get a replacement VIC chip?

    Tarnish on 74LS629:
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  4. retro

    retro Resigned from mod duty 15 March 2018

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    What are we looking at? It looks fine. It's an oscillator... use an oscilloscope.

    Uhh, best place to get a custom chip discontinued 20 years ago? Another machine. They're often more expensive than a PSU. And you're not guaranteed it's the chip at fault, or JUST the chip.
     
    Last edited: Nov 15, 2014
  5. RetroSwim

    RetroSwim <B>Site Supporter 2013</B><BR><B>Site Supporter 20

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