Help with repairing a Mac Plus

Discussion in 'Apple Collectors' started by ajc909, Aug 22, 2016.

  1. ajc909 macrumors newbie

    Aug 22, 2016
    Okay so I have a 1985 beige mac plus that works, with a bad floppy drive. Somebody said it was some sort of special early model and that over the years they had upgraded it to a 1MB with a kit. I'm using it for parts.

    The other one is a Mac Plus 1MB that is pure white. When I turn it on I hear the high pitch whine, the screen is inert, and I also hear a slight crank noise for half a second. I have a major problem now though, I saw smoke, and upon investigation I narrowed down the component. I hope the board isn't too badly damaged.

    Here are some pictures of the component in question, you'll notice brown burn marks around where it connects to the board.
  2. MacTech68 macrumors 68020


    Mar 16, 2008
    Australia, Perth
    Looking at the photos, I suspect that the problem may be the insulating tube encasing the yoke cables is melting on the Horizontal Output Transistor's heatsink. The issue will be how far it has burnt thru. IE, has it burnt thru any of the 4 cables inside to bare wire.

    Burnt Melted.jpg

    Usually, when the H.O.T. fails, the heatsink will be a lovely purple and blue color. I'm not seeing that here, so it's possibly OK.

    If the wires look ok, carefully unplug the cable, twist it 360 degrees and plug it in. That MIGHT keep it away from the heatsink.

    As for the high pitched whine, a video with the sound may help to pin-point what it is, unless it's the heatsink shorting onto one of the yoke wires.

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