Advice about repairing an IBM 5151

[william degnan]

often the card is the culprit, sometimes shorting out the entire sytem.

On Sat, Aug 29, 2015 at 9:24 PM, Vlad Stamate <vlad.stamate at gmail.com>
wrote:

> I have a normal IBM PC 5150 (not a 5155) with the usual MDA card
> inside. So when the computer is on, no picture comes on the monitor.
> So I am trying to diagnose that.
>
> (on a side note I do have a few of both monochrome cards as well as
> another IBM PC XT - 5160 as well as 2 other 286 based machines I can
> try, just in case the issue is NOT with the monochrome monitor but
> with the card/PC assembly).
>
> Regards,
> Vlad.
>
> On 29 August 2015 at 21:17, william degnan <billdegnan at gmail.com> wrote:
> > 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.
> > .
> >
> http://vintagecomputer.net/ibm/5155/ibm5155_monitor_connector_cga_card_closeup.jpg
> >
> >
> > On Sat, Aug 29, 2015 at 9:07 PM, Vlad Stamate <vlad.stamate at gmail.com>
> > wrote:
> >
> >> 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.
> >>
> >
> >
> >
> > --
> > Bill
> > vintagecomputer.net
>



-- 
Bill
vintagecomputer.net