Author Topic: Samsung UA32H4000AW LED TV Backlight Very Dim  (Read 2635 times)

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Offline quadTopic starter

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Samsung UA32H4000AW LED TV Backlight Very Dim
« on: December 08, 2016, 11:46:01 pm »
Hi,

My Samsung 32" UA32H4000AW LED TV - backlight is very very dim, can still see moving images on the TV but barely.

I couldn't find a schematic online, the board number is L32S0_EHS - BN44-00696B

What I've tried:

EDIT: I think I messed up my testing points. Retested with 3+ to 3- etc.

Measured the power to LED strips (top right connector on power supply board), labelled CNL802. The output rating listed is 76V @ 450mA

With TV switched on, and LED strips plugged in:

3+ -> 17.45 V
2+ -> 14.8 V
1+ -> 61.5 V

With TV switched on, and LED strips unplugged:

3+ -> 0 V (in the mVs)
2+ -> 0 V (in the mVs)
1+ -> 0 V (in the mVs)

All measurements taken with the negative probe connected to the corresponding "-" point  e.g. 3+ to 3-. 2+ to 2-

And TV switched on, LED strips unplugged, this time measuring 3+,2+,1+ to chassis

3+ -> 130 V
2+ -> 0 V
1+ -> 0 V

So I think it's a power supply board issue.

Any ideas? Thanks

High res photos:

Back of TV: https://postimg.org/image/eq68hb75r/

Front of power board: https://postimg.org/image/b4m3q2tt5/

Back of power board: https://postimg.org/image/kemcz2ly1/
« Last Edit: December 09, 2016, 12:23:16 am by quad »
 

Offline KhronX

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Re: Samsung UA32H4000AW LED TV Backlight Very Dim
« Reply #1 on: December 22, 2016, 01:13:57 pm »
You might want to check if both rectifier diodes are ok (you'll need to desolder one end of one of them, to be able to test them separately), DM854C and DM856C. Possibly D9151C as well.

That being said, i don't 100% trust CM856 and the one above it, either (the 250v electrolytic capacitors next to the above-mentioned diodes.

It looks like they've included a handy current shunt, to measure the total LED current as well. See that red polypropylene(?) cap between L9151CS and CNL802? On the back of the board, between TP1 and TP2 there's a parallel pair of 2 \$\Omega\$ resistors, so measuring across those on the mV scale will give you a mA figure.
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