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Hitachi LCD 42HBT42u Issues, Stanby Lights Flashe but Screen is Blank

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jjuk26:
Hi Guys, i have a Hitachi 42hbt42u LCD tv, yesterday the TV was on one minute then it went off, i have tried to reset as per the manual but no joy, im assuming one of the PCB has failed can you help. The tv is now out of warranty and i have sent refurbished PCB online at a reasonable cost, i would like to diagnose the right one though.

I have attached 4 pics on of the model and make, the other 3 are of the PCB at the rear of the boiler, there is no visible signs of damage and no smell of burning, how would i proceed to locate the fault, im a boiler engineer so i do have some knowledge of PCBs

Thanks in advance for any help

Jason

Davy:
Does it flash continuously or does it flash a number of time with a pause and then repeats? If so this would indicate an error code and would aid diagnosis.

Check for bad electrolytic capacitors, usually on the power supply board, their tops should be nice n' flat, not domed or leaking from the top or bottom.

Beware:
One side if the power supply is at mains potential - not isolated from the mains ( isolation is done on the chopper (switch-mode) transformer.  The mains is rectified so discharge the mains smoothing capacitor first, typical value would be about 150uF at 450V or so - this devil packs a hefty punch! I use a small 25Watt 240V incandescent lamp, you can use a resistor say a 1K ohm 2 Watt - shorting the capacitor out with a screwdriver doesn't help any apart from leaving a flash mark in the screwdriver or whatever you use.

'It's the volts that jolt and the mils that kill' (1mil = 1 mA or 0.001 Amp)

Dave

t1412:
hi test all the large diodes, you my find one that is short circuit, if there is one i'd replace all of them, thanks

shaun 

jjuk26:
Hi Guys, just to add:

I have looked over the boards and can see no domed or leaking components, i will try to check the large diodes to see if they have short circuit.

When i switch power on for the first time the standby light flashes 7 times

When i press the standby button on the remote the light flashes 13 times and then goes off

When i press standby again it flashes once

Does this mean anything to you guys

Thanks

Jason

jjuk26:
Hi Guys, just an update i have noticed that i can see a picture if i shine a bright light at the screen, i have tested the voltage to the LED drivers and this starts at 80-90 then decreases, would this indicate a fault with the LED/LCD?

Thanks

Jason

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