Infocus lp350 power supply issue

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#5
Infocus LP350 Power Board

I have an Infocus LP350 Projector which just died today. I discovered the problem to be in the marked part on the power board shown below.

An externally hosted image should be here but it was not working when we last tested it.


From my basic knowledge, I assume this part is a voltage regulator. I am posting here in hopes to get a more experienced diagnosis. Does anyone know what this part and it's specs are so I may find a replacement?

Thanks for any help.
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#9
There is a high voltage diode mod I do to these power supplies now, that prevents the meltdown of the entire power supply in the event the viper fails again.

What happens is when the viper fails, the power factor corrector voltage of 400V passes down the VCC pin that normally has about 13V. thus blowing up the entire power supply including the 100uf 25v filter capacitor.

Ever since the economy slumber, I havent seen or repaired any power supplies in quite some time. but i used to repair these things by the teens and 20s. But i still am open for repairs if anyone gets over their head. just PM me.


the ultimatum is the MOSFET inside the Viper100 shorts. this is because the 100UF cap that sits next to it, dries up. this causes noise on the VCC supply pin that powers the logic circuits that reside internal to the Viper100A. This causes spikes on the gate of the MOSFET internal to the Viper100A, causing mass-self-destruction of the entire power supply.

The spikes will make it through the transformer onto the secondary side. This sometimes causes the 12V secondary rectifier diode to short. When this happens, the filter capacitors becomes a reactance to AC voltage, of near 0 ohms. this causes a current overload, blowing the MOSFET internal to the viper100A, thus blowing the entire viper100A apart. sending hundreds of volts down the logical circuits inside the Viper100A, blowing up the Viper100A's VCC supply regulator. this also blows the opto-isolator that regulates the main supply.

Then the main supply shuts down, and is dead forever to come until repaired.

Another thing that happens is sometimes when the lamps wear out, the power factor corrector circuit that boosts your voltage up to 400V, the inductor starts to short, develops shorted turns, overheats, etc... this will cause instant destruction of the associated MOSFET and the L6561D driver circuitry. sometimes it will blow the zener diode out with it, it sits inside an SO-23 package.

the diode mod i do, is a 2 amp 800V diode that goes in between the viper100A VCC supply pin, and the supply regulator on the power supply board. When the MOSFET inside the Viper100A shorts again, this blocking diode will block the reverse flow of 400V into the power supply, protecting it from mass destruction. Then only simply changing the output diode and Viper100A would restore the power supply into full operation once again.

Another thing that can be done is adding a fuse in the B+ boost supply to the Viper100A regulator. use an amperage that is same or near the maximum current rating of the MOSFET of the viper. if MOSFET shorts, it will pop the fuse without blowing the viper to bits and everything else with it.

Viper100A is rated for MAX 100watt power supply. 100watts at 400V is 4amps max current draw from viper100a before its ratings are exceeded.
 
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#10
Although that is a bit over my head, I somewhat grasp the gist. It makes sense too since the replacement part I bought (shown in the link on my last post) did not work either because it was an incorrect replacement or due to the factors you mentioned.

In any case I am weighing out my options between selling it on ebay for parts, finding a replacement supply or having this one repaired. I have a decent backup projector I can use in the meantime.

What is your ballpark rate to repair my power supply knowing what you know about it now?

I can provide additional info if needed.

Thanks,

Mike
 
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