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

[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

[t1412]

yes 

[downunder]

If you can see video info on the screen, one could assume the 3 boards shown in your pictures are operating normally. Chances are you have a faulty LED or LEDs in the backlight unit as t1412 suggests.   -   Bruce

[jjuk26]

Thanks guys, im guessing its not the easiest to replace, looks like a new tv :(

Jason

[Turnip]

Hi Jason,

Notice set uses Vestel boards, and if it's a Vestel screen it probably uses LG Leds, famed for going short or open circuit.

As set is otherwise scrap, you might like try sort it, maybe just for the fun if you're minded that way as a boiler engineer with a test meter.

There's lots of recent pertinent screen repair info on Quuq, and new LG Leds are available on Ebay at £10 per hundred, where you'll probably need just two or three - This time.

Plenty left for next  - Chris.

[vinceroger69]

Hi Jason,

Notice set uses Vestel boards, and if it's a Vestel screen it probably uses LG Leds, famed for going short or open circuit.

As set is otherwise scrap, you might like try sort it, maybe just for the fun if you're minded that way as a boiler engineer with a test meter.

There's lots of recent pertinent screen repair info on Quuq, and new LG Leds are available on Ebay at £10 per hundred, where you'll probably need just two or three - This time.

Plenty left for next  - Chris.

Hi have you got a link too the ebay leds at that price you cant go wrong. Have you used these yourself? is there any noticable colour diffrence? as some of these cheaper leds do vary in colour

[Turnip]

Hi Vince,

They're listed as -

100/500/1000pcs High Power LG 110LM 1watt 3528 LED Backlight Television Backlit

They certainly look the biz in all respects with the 'large' heat sink area underneath that other Leds don't have. They look just like the originals.

Not yet tried any as still using screen-smash diodes - Will be nice to use new ones though - Chris.

[jjuk26]

Hi Turnip, thanks i will give it a try is there a guide to removing the screen to expose the LEDs that you would recommend, i see the lights in your last post are strip LEDs, is there also a guide to replace?

Thanks

Jason

[vinceroger69]

Hi Vince,

They're listed as -

100/500/1000pcs High Power LG 110LM 1watt 3528 LED Backlight Television Backlit

They certainly look the biz in all respects with the 'large' heat sink area underneath that other Leds don't have. They look just like the originals.

Not yet tried any as still using screen-smash diodes - Will be nice to use new ones though - Chris.

Thank you will order some and give them a try.

[vinceroger69]

Hi Turnip, thanks i will give it a try is there a guide to removing the screen to expose the LEDs that you would recommend, i see the lights in your last post are strip LEDs, is there also a guide to replace?

Thanks

Jason

This guide is good on a lcd tv strip down
https://www.youtube.com/watch?v=Bf5T2wwtydY&list=WL&index=102

This is a good video on how to replace single leds
https://www.youtube.com/watch?v=EZVQKEp6jxk

Athough i tend to just use a heat gun on the underside of the led strip once the solder melts the led comes off easily

[jjuk26]

Hi Guys, i ahve stripped the tv and have the strip lights are now accessible but i only have a mulitmeter on the video shown the guys is able to put 24v onto the led strip light, how would i go about this without purchasing extra equipment, i have a basic fluke mulitmeter

Thanks

Jason