Samsung LE40C530 40" LCD, Sound (probably) no backlights

[SuperSkippy]

I'm currently trying to fix this LE40C530 TV. The "big picture problem" is that it seems to turn on but there is no picture. The backlights do not fire.

This TV has the inverter power supply on the power supply. This isn't my picture, but it's the same power supply as the board I've got.



The power supply is model BN44-00340B. You can get the circuit diagram from


What I've done is I noticed that the two MOSFETs had blown on the inverter section (they are labelled QI809 and QI825, if you can be bothered to get the circuit diagram). I've replaced them with similar, but not identical, MOSFETs (the ones I bought are https://uk.rs-online.com/web/p/mosfe...hTerm=419-2204, whereas the originals are https://cdn.badcaps-static.com/pdfs/...b42f87e745.pdf)

Having replaced these MOSFETs, it still doesn't work. When you apply power to the set, it sits there for a minute then tries to turn on. At this point the gate pin on the Mosfets show 5V if I put a multimeter on Volt mode, and about 50kHz if I put my multimeter on frequency mode, so I think the MOSFETs are being driven.

This board has two connectors to the inverter board- one with 7 pins for controlling the inverter, and a bigish one that supples the high voltage. On the small one, there are some feedback pins- I never see any voltage on these.

I haven't been able to find out if there is actually any high voltage power going to the inverter board, as it says 800V AC on the power supply board, but my multimeter is only rated for 750V AC, and is fairly Chinese and ropy, so I'm not keen on blowing it up.

All other voltages on the power supply seem OK.

Any tips welcome.

[SuperSkippy]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

I could just buy a new power supply as they are cheap and plentiful, but I don't want to be a board swapper, and besides it could be the inverter board, and I'd have wasted my money.

[tom66]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Check fuse FI801S is not blown.
Also, check the voltages across CP801, CP802 (the yellow 450V caps) it should be around 380 to 400V.

[SuperSkippy]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Check fuse FI801S is not blown.

Yep. I feel such a dum dum.

[tom66]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

So, it is blown, or not?

[SuperSkippy]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Yep. I feel such a dum dum.

You got any idea what kind of fuse I should replace it with? The fuse I've got is plain white, and the circuit diagram says T3.15AH, 250V, which is not that helpful.

[SuperSkippy]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

So, it is blown, or not?

Yep, blown.

[tom66]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

You want a

T3.15AH 250V fuse

which is a 3.15A, Time Delay, 250V rated 5mm x 20mm cartridge fuse.

It must be ceramic body construction, glass will be unsafe.

[SuperSkippy]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

That's fixed it, thanks!

[tom66]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Glad to hear, another one saved from landfill.

[matyka]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Hello,I have just purchased the same model samsung .
I have sound but no backlight .
I have tested the fuse and is ok.No short MOSFETs.
Could be the inverter defective ?
Thanks in advance.

[matyka]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

The power supply is model BN44-00340A

[tom66]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Check voltage across 400V caps - should be ~390V.
Also check if the backlights turn on when the main board connector is removed. If they do the main board is at fault.

[matyka]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Hello,I have ~150v between the big caps they are rated 150v~
The power supply is model BN44-00340A and is different from BN44-00340B and they do the same thing. The BN44-00340B has ~450v caps .
By removing the connector from main board and shorted the P-on with 5V and 5Vdet with invert on/off I have no backlight staying .I think the power supply is not working properly ?
Any idea ?

[budm]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Hello,I have ~150v between the big caps they are rated 150v~
The power supply is model BN44-00340A and is different from BN44-00340B and they do the same thing. The BN44-00340B has ~450v caps .
By removing the connector from main board and shorted the P-on with 5V and 5Vdet with invert on/off I have no backlight staying .I think the power supply is not working properly ?
Any idea ?

You better verify that your meter is OK, you country AC is around 230VAC so the DCV measured BETWEEN the two legs of the main filter caps should have about 330VDC when the PFC Voltage booster is not on, and close to 400VDC when it is running.
BTW, what do mean by the filter caps are rated at 150V? I see 450VDC rating on them (shopjimmy site). Some one worked on this board before? I see 100uF 450vdc on your picture.

[matyka]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Thank you for your reply.I just re-checked and yes both you are right ,the 2 caps have 450v and when reading them they are read between 320v-410v.
I tried and disconnected the main board from the power supply and powered on the power board- the backlights stays on .
This mean the main board is faulty like Tom said ?
Thx

[matyka]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Hello,I have found the problem why I have no backlight .
After I replaced the main board I decided to open up the tv and check the lamps.I have one bad one and one flickers .
Anybody selling this lamps ?

[hedgeville]

Re: Samsung LE40C530 40" LCD, Sound (probably) no backlights

Our LE40C530F1W has started to fail after reading forums like this one we have tried to repair the PSU (BN44-00340b)
The TV itself will come on after 5 flashes of the red led if it's been off a good while or unplugged and the power button held for 10 -15 seconds.
Once the TV is on its absolutely fine but if placed in standby it wont come on atall although a couple of days ago it took a good few minutes to start up but now it just wont start dark screen no image behind and no power red light.
So today we decided that all the secondary (cold ) stage capacitors were changed. None of them appeared bulged or leaky but I know this doesnt nessasaily mean they are failing.
Unfortunately this hasnt changed anything atall. The TV still refuses to come on from standby if its been on.
Their doesnt seem to be anythiing too obvious, the fuses are intact not suprisingly as it working sometimes?!

Can anyone advise where to start with any further diagnostics.

Many thanks