Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: jjuk26 on March 07, 2017,13:29:14
-
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
-
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
-
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
-
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
-
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
-
yes :03:
-
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
-
Thanks guys, im guessing its not the easiest to replace, looks like a new tv :(
Jason
-
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 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
-
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.
-
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
-
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.
-
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
-
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
-
If you have access to the terminals on each LED, the Fluke in diode mode should illuminate each individual LED (This is not always the case). The polarity of the meter leads is important. If no light when connected one way, try reversing the leads.
If not, count the number of diodes in each strip, multiply it by 3 (3V per LED) gives you the voltage you need to apply to the input of each strip. So a strip of 12 LEDs will need 36V. Any strip that doesn't light up will have faulty LED/LEDs on it. Heat discolouration on a particular LED may give it away.
Most of us have a LED tester by now. Connect it to a strip, and it automatically adjusts the voltage up until the strip lights up.
-
you can use two aa batteries like in this video some people also test the leds in each direction using the diode mode on there multimeter
https://www.youtube.com/watch?v=eEJoPCa7Kt0
https://www.youtube.com/watch?v=ZSJ4ETkLTF4
https://www.youtube.com/watch?v=K_VfM4grw3I
https://www.youtube.com/watch?v=YgaL6X6eSaU proper led tester
-
Hi Guys, i wired up an 18volt drill battery and tested, the one strip did not work, there is a strip on eBay for sale but its a used one do you know the best place to get a new one?
LB43007 VO_01_38S
KS-D 94V-0 E465853 15 16 (IN GOLD BIGGER WRITING) 7193A 81010
17DLB43VLXR1 and the letter A
Thanks
Jason
-
Hi,
When first trying check Leds, I assumed that the Copper area either side on the strip was anode/cathode. It isn't of course, just the heat sink connected to the larger cathode area of the Led.
The anode connection is to a thin printed track leading to the next Led in line, and next to the -ve which runs along the length of the strip (With usual LG strips)
Currently use a current limited power supply but notice China does automatic Led testers showing voltage and current for less than £15.00 inc post - Chris.
-
Hi Turnip, thanks i have located the faulty strip, just need to know best place to purchase now :)
Thanks
Jason
-
Hi Turnip, thanks i have located the faulty strip, just need to know best place to purchase now :)
Thanks
Jason
If your in the uk you can try ohms supplies, how many leds have failed on yours? as maybe possible to replace them all in one go
-
Hi Vinceroger69, the whole strip has gone
Thanks
Jason
-
I have never had a whole strip go before yes one or two have you tested each led with 3v battery? as if one is shorted may stop the whole strip lighting up and depending on what lcd panel your set uses maybe this strip
http://www.ohmsupplies.co.uk/epages/62027733.sf/en_GB/?ObjectPath=/Shops/62027733/Products/LED13-Z1.01
-
Just wondering that's all. If one or more LED's have gone, would it not be better to change the entire lot and have done, better than to do it once than keep having to do it, my way of thinking is when are the others going to 'pop their clogs'.... might be next week or never?
Dave
-
Just wondering that's all. If one or more LED's have gone, would it not be better to change the entire lot and have done, better than to do it once than keep having to do it, my way of thinking is when are the others going to 'pop their clogs'.... might be next week or never?
Dave
yes this is my thoughts too now, as in changing the lot in one go then turn down backlight level as should last a lot longer then as each time you have to strip the lcd panel down more chance of cracking it or tab bond damage.
-
when you replace the led strips is it best to do a firmware updated if possible thanks
shaun