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Thread: Sanyo MBC-775 #1 Problems (Same from "Question About CGA/EGA Cards..." Thread)

  1. #11
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    254

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    Ok, I tried replacing the capacitors in the power supply, but I'm back to square one. No raster, no response, nothing. I actually had to take two of the capacitors down a voltage rating [from 100v down to 50v] because I didn't have the proper component. It's basic logic. All of the other capacitors are in the same range, and it's plausible to assume that some of those capacitors are only used for the capacitance rating, not the voltage rating.

    Anyways, I can't find anything obviously wrong with the decoupling capacitors. I have quite a few filter capacitors on the motherboard (many with two ferrite cores added to each capacitor assembly). I'm not sure where to start right now.

    What makes the computer odd is that it uses a pin header connector with a secondary board that contains the processor, what I assume is the BIOS, and all the memory, so it's not a matter of taking out any faulty cards.
    Last edited by T-Squared; August 22nd, 2019 at 05:16 PM.

  2. #12
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    254

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    LIFE! I HAVE LIFE!!!!!!



    Well, not exactly.

    I have progress! I got a beep (one single strong beep) from the speaker after using Adrian Black's method of finding bad tantalum capacitors, and reseating the CPU. One capacitor looked suspicious after it showed slightly lower resistance. It still showed the same thing after I put in a replacement capacitor. Maybe the CPU wasn't making good contact?

    The composite video output is also unstable. It actually looks like it's resetting, for some reason. I also can't get any kind of image (i.e. completely blank black) on the internal monitor.

  3. #13
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    254

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    HOLY CRAP! (as a 1980s-electronics-using boxing-gloved wrestleman once said...)

    I thought about checking for some weak joints in the CRT electronics, since I could not get an image on the screen, AND WHAT DO I FIND?!

    20190829_232233.jpg

    Yep, the CRT control board is completely cracked. You will be able to see it right next to the ring of solder points that make up the flyback transformer.

    I'm not giving up, though. I have an idea...

  4. #14
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    254

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    I'd like some help identifying what these connectors are called, if possible. They look like Molex-type and are usually found in TVs, but multiple searches have turned up nothing similar.

    connector1.jpg

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