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Thread: IBM 5153 rolling screen / Vertical sync lost?

  1. #1

    Default IBM 5153 rolling screen / Vertical sync lost?

    Hi,

    I just bought an IBM 5160 XT with a 5153 CGA monitor. On first power up computer exploded, and on closer check up it turned out capacitor on C56 had blown. Next I removed both capacitors C56 and C58 and got mainboard running again.

    Now I have a new problem, 5153 is not working as it should.. picture rolls from top to bottom. Here is video showing what´s going on:



    Any ideas how to fix it, or what could cause screen rolling?

  2. #2

    Default

    No doubt you have tried all positions of the V hold control on the monitor rear panel ? If the Vertical sync feed is totally open then adjusting the control wouldn't lock it at all and it would still be drifting up or down, depending on the position of the V hold control. Is that what happens when you adjust the control or is there a tendency for some vertical lock when the image drift rate is low ?

    If the V hold control can't lock the image then you need to investigate the path of the vertical sync pulses. The vertical sync comes in on the cable directly on pin 9 of the plug that plugs into your video card on the computer, so the first thing to check is that the vertical sync pulse is actually present and the cable is not fractured or the wire broken from the pin in the D connector assembly (people love to pull on cables & not the plug bodies).

    On the main monitor pcb the sync pulse passes directly via a 3k9 resistor R311 and 1uF coupling capacitor C302 into pin 7 the HA11235 vertical sync processor IC.

    There is also a (C301) 0.033uF capacitor to ground to filter off high frequencies. Since that IC is working to generate the V scan, I doubt if just the sync section of it has failed, but its possible. Most likely the cable/connector is faulty (unless your video card is faulty) or C302 the 1uF capacitor has lost nearly all its capacity(dried out) or the 3k9 resistor is open(unlikely) or the 0.033uF cap shorted (unlikely).

    If the V hold control seems to be out of range and it reduces the roll rate, but can't lock the image, check the DC voltages on the HA11235 IC.

  3. #3

    Default

    Thanks, adjusting the V hold control did the trick! I was not aware of the knobs on the back of the monitor.

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