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Thread: Ti-99/4a issue

  1. #1

    Default Ti-99/4a issue

    So I finally got around to tearing apart and testing my ti, (making a restore vid) and ran into an issue. Upon power up, only static woth a light buzz. I removed and resocketed the video, grom, and sound chip with no change. All chips seem to have voltage and ground at the correct pins. But nothing has changed, only outputs static and a buzz. The buzz changes pitch when key pressed.
    I'm leaning towards the video chip being bad, but wanting to hear from someone that had similar issue.

  2. #2
    Join Date
    Oct 2016
    Location
    Cincinnati, Ohio USA
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    438

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    Quote Originally Posted by New2vtgpc View Post
    So I finally got around to tearing apart and testing my ti, (making a restore vid) and ran into an issue. Upon power up, only static woth a light buzz. I removed and resocketed the video, grom, and sound chip with no change. All chips seem to have voltage and ground at the correct pins. But nothing has changed, only outputs static and a buzz. The buzz changes pitch when key pressed.
    I'm leaning towards the video chip being bad, but wanting to hear from someone that had similar issue.
    I am far from being an expert, but I have watched lots of youtube repair videos. If you can get a known good video chip, that would be a reasonable plae to start, since it is the only socketed chip. If that isn't it, you probably need to get an oscilloscope and start checking activity on address, data, and chip control pins to try to narrow it down. You did check all three voltages? Also, leaving it on for a while and checking the ram chips to see if any are extra toasty might indicate a bad RAM.
    PCjr, DTK PC-XT Turbo, 386DX 33, 486 laptop, Pentium 120, Pentium III 500, various old laptops, Commodore Colt, all working. I also have a 286 that I need to see if I can repair.

  3. #3

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    Quote Originally Posted by KenEG View Post
    I am far from being an expert, but I have watched lots of youtube repair videos. If you can get a known good video chip, that would be a reasonable plae to start, since it is the only socketed chip. If that isn't it, you probably need to get an oscilloscope and start checking activity on address, data, and chip control pins to try to narrow it down. You did check all three voltages? Also, leaving it on for a while and checking the ram chips to see if any are extra toasty might indicate a bad RAM.
    Yep. I checked all those. I didnt have an oscilloscope but set my dvom to hz and looked for frequency.
    No change...until I set my meter down on the rf cable on the back and picture showed up. Someone previous attempted a repair...but stripping wires, wrapping around the din pins on back and hotgluing them in place....
    Soldered it right and works like a charm.
    Oh and on the biege models the grom and sound chip socketed as Well

  4. #4
    Join Date
    Oct 2016
    Location
    Cincinnati, Ohio USA
    Posts
    438

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    Great. Glad you got it working. I hate coming along behind someone who did a lousy repair. A lot of time undoing what they did is harder than doing the repair right.
    PCjr, DTK PC-XT Turbo, 386DX 33, 486 laptop, Pentium 120, Pentium III 500, various old laptops, Commodore Colt, all working. I also have a 286 that I need to see if I can repair.

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