Advice about repairing an IBM 5151

william degnan billdegnan at
Sat Aug 29 20:17:18 CDT 2015

There is a 2nd connector for the video card of the 5151. I can't quite tell
if you mean you have the video card that comes with the 5155 and you're
trying to test with a card that came from somewhere else or something else.
I am unsure if the 2nd connector pertains to the internal or external port,
but you want to be sure you have this in place.

On Sat, Aug 29, 2015 at 9:07 PM, Vlad Stamate <vlad.stamate at>

> Hi all,
> I am trying to identify why my IBM 5151 display has no picture when
> connected to a normal MDA card in a IBM PC 5150. So armed with an
> oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
> started to investigate. First, the card does send out signal and that
> signal does reach the board inside the monitor. I checked the power
> part of the circuit, all diodes and the transistor check fine. I
> probed some of the vertical and horizontal transistors and there is a
> signal there too. Then on the video board both TR19 and TR20 have on
> their collector and emitter (respectively) a signal (95Khz). What else
> can possibly be wrong?
> The SAMS manual talks about "injecting a video signal" at different
> pins however I have no idea exactly how to do that.
> So there is current going out of the power part and there is signal on
> the video board attached to the neck of the CRT.
> Regards,
> Vlad.


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