NEC DM-2710 Professional Video Monitor Repair

[Shibby]

Originally Posted by zeno

Unplug the degauss coil !!
Measure the AC amps at turn on. It should be < 1 amp.
If over its over current

Measure amps where the degauss coil connects?

Originally Posted by zeno

Measure the HV at turn on OR usually the 200V supply to
the 3 video outputs. If high its over voltage.

I don't have a KV capable tester so i'll try the 200v supply.

[zeno]

Originally Posted by Shibby

Measure amps where the degauss coil connects?


I don't have a KV capable tester so i'll try the 200v supply.

Measure total amps at AC input. Reason to unplug the DGS is when
you turn on it will draw a LOT of current for a second & it will go
into HVSD before it drops.

[Shibby]

Originally Posted by walterbeers

I would assume that the 200v supply is running too high, causing the monitor to shut down. One problem I have run into in the past is that there may be a B+ adjustment on the PC board, (usually a very small trimmer pot) also glued into place and position by this nasty glue stuff. The idea of gluing it was to keep anyone from tampering with it, thus causing the B+ to run to high. Most times the only fix is to replace the pot, and adjusting it to the proper voltage.

I believe the only trimmer that was covered like this was for the HV adjustment which I guess could actually be an adjustment for the B+ if I understand B+ correctly. Per the service manual when testing power issues I am supposed to turn the 3K pot fully counter clockwise then measure HV and adjust from there. Well of course in the process of pulling the cap and goo off the pot it ripped off the board. I bought and installed a new one but it doesnt seem to be making a difference. I may not have actually measured B+ though while adjusting the trimmer. Either way no matter where that trimmer is it still wont produce constant HV.

Originally Posted by zeno

Measure total amps at AC input. Reason to unplug the DGS is when
you turn on it will draw a LOT of current for a second & it will go
into HVSD before it drops.

I will be doing this tonight and will report back. Sorry I have been distracted by some reel to reel goodness

[andy]

...

[Shibby]

Originally Posted by andy

The first thing you need to do is verify that the low voltage power supply is regulating properly. Does it have a switching power supply, or a linear voltage regulator?

If it's a switching power supply, is the power supply shutting down, or just the horizontal sweep/HV?

If it's a linear power supply, it's common for the regulator IC to short causing excessive B+ and HV shutdown. You can do a quick test for this by running it at reduced line voltage using a variac.

I don't suppose it has any large ICs in sockets? NEC had problems with IC sockets in the 80's that would cause all kinds of trouble. The solution was to get rid of the socket and solder the IC directly to the board.

A few good pictures of the inside might prompt some more suggestions.

These really do sound like very good suggestions but I believe at this level it is where it begins to start going over my head. Unfortunately I do not have a variac and I am unsure what type of power supply it is. Is there something simple I can look for to help identify the type? As far as the IC's go I dont believe that any are socketed but I will go back over it and check.