Hey

Í'm trying to repair the powersupply in a MX3500.

I think the fault is caused by by the TR1. I'm having some trouble trying to find a replacement. Do any of you know any cross reference to the BUT12F transistor?

Update: Seems like BUT 76A is a good replacement, http://www.datasheetarchive.com/crossreference/BUT12F.html.

Below you can see some photos of the print. The inductor L5 has a black hole around one of the pins.

If you have some good advice on this fault, please let me know. 

Unsolder L5, repair it with epoxy glue or replace it. This fault is quite common, i had already several of these defects. The reason are vibrations and a cold spot after this long time. Use also some epoxy to fix L5 on the board.

Replace also C5 6.8nF 630V and the BUT12. C5 becomes bad and the switching frequency becomes higher and higher until BUT12 failes.

Fantastic with such a comprehensive guide!

I have been saving money for a mx3500, and when I finally bought one, I was fooled. The TV I bought works for 2-3 minutes, and then I get a blue screen with white stripes across it. Sometimes it changes to green or purple, sometimes the real picture comes back on. The sound is working. Does anyone have an idea what could be wrong? Could it be bad caps and if so, which ones?

I have some experience with electronics and high voltage, but not enough to locate the error.

I can mail a picture of the error, but since I don't have a web hotel I can't upload it here.

Any help would be much appreciated. Thank you

Hi,

this sounds like a broken copper wire on the Pal-decoder RGB Board. Check the ground connections and the 8V supply line. I think, it could be the broken ground line  ;)

Defect caps are always possible on these old boards... and after 20 years a lot of them are gone. It's always a good idea to replace them. But this fault is the RGB driver board. I had last week just this fault on a LX5500...

Martin

Hi Die_Bogener.

Thank you very much for your reply! I have now checked the ground connections and 8v supply line on the RGB-board - all of them seems to be allright. But perhaps it's because the pcb is cold, and the connections fails when it warms up? Anyway, can I connect the 2pin ground with the mentioned IC-pins directly with a wire? Then I will be sure that the connections are allright... But maybe this will shortcut the pcb? Could be fantastic to bring the MX back to life.

-Thank you in advance. 

-Andreas

Hello Die_Bogener!

I have an old MX6000 CRT that has started to behave really strange. When I start it it turns green just as normal, but as soon as the picture starts showing, is turns itself off immediately. The model is not one of the listed ones in your topic, but I thought I would ask anyway.

I started it in Video, with nothing connected, and it was fine (black, offcourse) until I connected my Popcorn Hour, at which point it turned itself off again.

Any hint of what might cause this would be very appriciated. The TV is superb as a second set, mostly serving my childrens movies from the Popcorn.