Sunday, June 10, 2012

Nec VT440 fix

I've bought a NEC beamer on the cheap (~30E) which ran for about 1 second before becoming dead.
In the interest of reference I'm attaching pictures taken with a phone camera so that other people know what they are getting themselves into.

I'm not really good with diagnostics but I have taken the whole thing apart and started probing for voltages. Voltage at the control buttons was measured at ~1V, which was quite far from the 3.3V I was expecting.

The problem turned out to be a blown SMD fuse, marked as 0F0 (or similar), rated to 2Amps, which I've replaced with a jumper wire rated at roughly the same amperage.

Interesting fact: the beamer case is painted with some metallic paint which is enough to conduct from about ~400V potential. I found out this the hard way by letting the lamp connectors rest on the case while testing. It produced a huge spark and the paint was stripped out for about 1sq cm at the two points of connection.
Lesson learned

View from above with case tken off:

Mainboard connector:

Mainboard view from below:

Enlarged view:

Another enlargement. The culprits were the small black things in line with the first connector. One of those was tested interrupted and subsequently replaced with a bent single-core wire.

Lamp housing, fresnel lens at the bottom:

Lens housing, 3xLCD connectors, vga signal (?) pcb:

Power supply housing at the left, isolated from  everything:

Power supply taken apart, bottom part is the rectification and switched supply. Top part is the lamp/bulb supply:

Details of main power supply:

Details of the lamp supply:

Bulb housing from above, the round thing with the thick wires is a temperature sensor for the lamp:

300-400V going through those thick wires, I don't have the measurement anymore:

Fan connector, I guess:

Sorry about the quality of the pictures and the explanations, this was done one year ago and I did not remember to take detailed pictures and mark down the measurements.

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