Atari 2600 - Video output issue

Discussion in 'Repair, Restoration, Conservation and Preservation' started by X5900, Sep 18, 2016.

  1. X5900

    X5900 Rising Member

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    I had an old 4-Switch Vader laying around, which I've bought on the flea market a few years ago as a spare unit. I really can't remember if I've ever tried to hook it up or not, but yesterday I did and all I got was a black screen.

    The board was in almost pristine condition, the only suspicious thing was a bent pin on the RIOT chip. This made me think that someone was in there before and possibly tried to fix the video issue by swapping chipsets. I didn't trust the 3 Main IC's after that and decided to swap them with known working ones. Since I had a working 2600 jr and a working Vader, paired with some free time, I've desoldered the CPU/TIA/RIOT from the 2600 jr and put them in the sockets on the Vader board.

    The result was that I now get a picture, but barely visible, I can make out the start screen of the game, but it's hidden under pretty heavy noise and distortions in the video output. The game logic does seem to work. Next thing I did was swapping out the RF unit with the known working one from my other Vader, but nothing changed, so the RF unit wasn't the problem either.

    Now I'm out of ideas, any suggestions would be greatly appreciated :)
     
  2. PIXeL92

    PIXeL92 Spirited Member

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    I know it may sound silly but check the voltage on the 5V regulator
     
  3. wilykat

    wilykat Site Supporter 2013

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    Original 7805 regulator often aren't made to last so long so some may be nearing 40 years old and are putting poor output. Just check using voltmeter from middle pin to one of the 2 outside pin. One side is input and comes from AC adapter. It should be around 9-11v DC when the system is on and may be higher when the system is off. If it's lower than 7, the AC adapter needs to be replaced. IIRC the earliest AC adapter were 300mA variety and did have issue with later games, Atari changed to 500mA at one time.

    If the input is higher than 7v DC and not really high, check the other side. It should be 4.75 t0 5.25v DC. If it's not there, replace 7805 and check the big cap. Generally that one doesn't need to be replaced unless it's leaking. Little green chiclet cap may however need to be replaced anyway.

    If you are getting near 5v DC and it's still fuzzy, there may be a problem somewhere else. Check that all 3 chips plus 4050 if it's present (usually near RF modulator) that it has a 5v DC on power input pin.

    Atariage and Console5 has free schematic you can download and use to probe for problem area.
     
  4. X5900

    X5900 Rising Member

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    Strange puppy that one. I've changed the 7805 to no effect (I was getting around 4.97V, so no surprise there). The chipset isn't the fault either, I've swapped them with 2 know good sets. I've even swapped out the RF units, still no luck. I can see the game logic works, it's just the video signal which is a noisy mess.
     
  5. wilykat

    wilykat Site Supporter 2013

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    That would narrow to somewhere between TIA and RF modulator. A bad solder joint, a way-off spec'd cap, or out of adjustment coil could do it.
     
  6. takeshi385

    takeshi385 Mojarra Frita Bandit

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    The caps are real issue in these consoles. The Green chicklets and electrolytic caps are known to die and they will affect video. I suggest replacing those and you should get video.
     
  7. X5900

    X5900 Rising Member

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    Got it, one of the resirtors has gone out of spec, works perfectly now. Thanks!
     

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