Mitsubishi 91TXM monitor - no picture

[Andy Harvilla]

Is anyone familiar with these older Diamond Pro monitors from
Mitsubishi? This one had about nine years of excellent use until I
powered it on one day. There was a little "pop" and a small dot of
intense white light appeared at the center of the display. The light
faded away after a few seconds and I haven't been able to get a picture
since. A few weeks before it failed, the screen tended to flicker
sporadically (high/low brightness).

After this happened I pulled the unit apart and starting checking
voltages and connections. I'm not really into electronics, but I learn
what I have to. I did not have HV and there was a pulsing noise every
few seconds, indicating to me that HV was trying to come up.

It turned out that the horizontal output transistor was bad, so I
replaced it. The pulsing sound is gone, HV is working, and I can change
the brightness by adjusting the screen voltage on the flyback
transformer (displays the horizontal retrace lines). Unfortunately, I
am unable to get a real picture when the monitor is plugged into a
computer.

I did some searching on the Internet and found a bunch of components
that are known to fail on these models (mostly resistors, but a few
capacitors). All of them seem to check out fine with my multimeter. Has
anyone experienced something like this before? I'm really at a loss as
to where I should go next.

Andy Harvilla

 

[Andy Harvilla]

I tinkered around with the monitor a little bit more and discovered
that there's a poor connection on the power supply board. There is a
transformer that makes an audible noise when the board is tapped or
gently moved. With that noise comes a change in the picture -- usually
just in terms of brightness, but I did get a few very bright bursts of
white (presumably due to a slight connection and maybe a spike in
power?).

Other times, though, the monitor powers on like normal, yet I'm still
seeing the horizontal raster lines. The screen control on the flyback
works as it should, and so does the focus.