Hitachi 37LD9000 Inverter tripping, Story in pictures

I would not leave that stryofoam in there, it could present a fire hazard.

Wasn't planning to, just a temp fix till i get appropriate feedback and find a solution, Thanks anyway Mr. Darby :)

I can see three approaches.

The first is a brute force approach. It depends on sufficient space between the perforated shield and the back of the TV. Judging by the styrofoam experiment, a rectangular 'can' of that depth could be constructed and the back shield modified so there is additional clearance between the transformers and the (extended) shield.

The second is more elegant and more work to achieve. Inverter controller ICs monitor a number of parameters, including output voltage, CCFL current, and even drive current. Determine which parameter is causing the shutdown. Then analyse the circuit to determine if the setting is overly conservative, components have drifted, or a component (driver?) is marginal for this application. The solution might be as simple as changing one resistor, or as complex as redesigning the driver circuitry.

The third is simple - check with Hitachi and determine if there is any modification kit to resolve this problem. I don't hold a lot of hope that there is, but ...

PlainBill

Thanks for respnding Bill :)

Brute force hammer n punch? i have clearance between back cover n shield

5 mm displacement? Wht if I cut another hole through? smd filter caps on board too? no schematics for inverter available, no marking on caps

How does the black patch and foil work anyways How do i word this innocently to Hitachi to get them to hep?

Well, I was thinking of something like a sheet metal nibbler (drill hole in sheet metal, tip of nibbler goes through, nibble out opening of any desired size ande shape). In this case, 'brute force' meant a solution which avoided the sensitivity to metal without actually repairing the design defect.

There is a hole in the inner shield, I'm guessing it's about 5 cm x 7 cm. I would cut a rectangular hole 6 cm x 8 cm in the perforated shield. Next, build a shallow rectangular pan 6 cm x 8 cm by 5 mm deep with a 5 mm outer rim. Finally, attach the pan over the opening you cut.

I don't have a clue.

Why be innocent? I would start out assertive - "What is the reference number for the service note, change order, or repair kit to solve the inverter shut down problem on a 37LD9000 TV?"

PlainBill

On Wed, 25 Nov 2009 22:10:44 -0800 (PST), jango2 put finger to keyboard and composed:

The datasheet for the Rohm BD9890FV inverter controller states that "a strong electromagnetic field may cause the IC to malfunction":

However, the above warning may be a general one, as it occurs alongside other general warnings including "mounting failures, such as misdirection or miscounts, may harm the device".

What if you tried shielding the BD9890FV IC inside a metal box ???

Or what about a grounded metal plate above it, and a plate below it on the underside of the PCB?

- Franc Zabkar

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