CurtPalme.com Home Theater Forum

seanoise · Joined: 16 Jun 2009 Posts: 29

hello!
i have a problem with my hdm.

yesterday i started my projector at first with 720p and all was fine. then i changed to 1080p and after 30 seconds the picture dissapeared and on the hdm the two diodes D21 and D22 died.
i changed them and started the projector again, at first with 720p, all worked fine again. and then with 1080p the same problem, after 30 seconds the picture dissapeared und the same two diodes died.
do you have an idea what als could be broken an the board???

mfg

seanoise · Joined: 16 Jun 2009 Posts: 29

it is a 08p hdm from a marquee 9500lc ultra

mp20748 · Posted: Tue Jul 20, 2010 12:00 pm Post subject:

Now that's one very unusual problem...

I've never had a problem with those diodes failing, and never heard of this until now.

Those two diodes are a part of a switch mode (buck converter) scan regulator circuit that converts the +85 volts from the LVPS to a variable negative voltage modulator circuit (Mod Supply). That circuit varies the negative voltage that operates the sweep circuits PowerFets and deflection drive for the scan yokes.

It varies the MOD voltage depending on the scan rate of the signal within the two deflection yoke bands.

For a problem like this i would seriously suggest that you either replace the HDM or send it to Curt for repair. That type of problem should be diagnosed using a test machine where the possibility of tube failure would not be a concern.

Marquees have the BEST power fail and scan fail circuits protection of any CRT projector out there, but it's not always something you'd want to gamble with, especially with a problem you're having in that particular circuit.

On a properly functioning Marquee, you could yank either vertical or horizontal deflection connectors loose from their connector, and the fail safe would respond fast enough to protect the tubes.... keep in mind i said on a "properly functioning Marquee"..