29 Aug
2015
29 Aug
'15
6:27 p.m.
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:
--
Bill
vintagecomputer.net
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_clos…
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