Mitsubishi DiamondPro 930SB, probably short somewhere

[Behemot]

Almost two weeks ago all of the display modes settings on this CRT broke up - every single mode got barrel shape. I changed the geometry and also played with sync on colors (it was going to purple and yellow in two corners). Monitor was fine than. Few days ago I finally got KVM switch working, than turned display off. It did not start again after couple of hours.

I hear repeated whistle, probably it's shorted somewhere. Now I have the board on floor, only with the electronic usually connected on the tube is plugged into high.votlage transformer. Did not find any of the bigger diodes or transistors shorted, any idea? Could that be the data part? Or the high-voltage transformer itself? There are bad caps but optically fine, image was still good to the last moment.

It got really excellent image so if I'd be able to fix it it would be good, if not I'll try to get another one, these 19"+ Trinitron CRT's no don cost much now. But still I am pissed of you know, I bought it not even year ago. I know that it was serviced one time, some problem with image at those times (image shrinked into one line).

[b700029]

Re: Mitsubishi DiamondPro 930SB, probably short somewhere

You describe typical trouble of this model. During working with some videocards (generally NVIDIA) monitor crashes his memory data. It’s bug of old version of monitor’s firmware. If your monitor had manufactured until April 2004, it contains old firmware version. After April 2004 this problem had fixed by manufacturer and all monitors contains new firmware. You can check firmware version in factory mode (to enter to factory mode: during pressing “+” and “-“ buttons simultaneously switch on the monitor, for exit from the burn in mode: during pressing “EXIT” button switch on the monitor). In this mode OSD menu became red and you can see firmware version at lover right corner of OSD menu. Old version is V2.7, new (with fixed bugs) – V3.2. Unfortunately, only NEC service partners can update firmware.

During servicing this monitor, be careful: heatsink of Q101 is under hot voltage and U401 heatsink connects to -14V rail. You must isolate them from monitor’s chassis. As I understand, power supply works in protection mode. Have you checked D151, D152, D153, D154, D155, Q314, Q151, Q153? In addition, you can check all secondary voltage rails to absence of shorts. Another typical trouble of the mentioned monitor is cold soldering of deflection coil connector as well as U401 and FBT. It can make sparking thru cracks in soldering and fault of Q314 or U401 hereupon. In some cases faults of video amplifier IC makes short of 12V rail too.

If only FBT is broken, the monitor indicates error code by front panel led flashing. Almost internal diagnostic system can indicate another troubles as deflection stop, IIC error etc.