Mitsubishi 91TXM monitor - no picture

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

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Andy Harvilla
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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.

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Andy Harvilla

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