Samsung LE32R74BDX Backlight flicker

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Hi

Got this one and it was dead traced the fault to the good old F9222L IC, replaced it and now the tv works fine bar the backlights are flickering.

Checking the 24V pin I am getting 21.1v one thing that I have noticed is that two Crapxon caps rated 1500 x 35 are in the board...I thought these were supposed to be 2200 x 35 but cant find a service manual to confirm

The psu is BN96-03775A

Thanks for any help

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

21.1V will cause flickering -- also check voltage across large 400V cap should have around 390V DC.

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Re: Samsung LE32R74BDX Backlight flicker

381v

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

Good.
Can we have a picture of the power supply?

Schematic:


shows them as 1500uF/35V.

Check if 13V line is bad too.

Consider CM802 as possible fault.

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Re: Samsung LE32R74BDX Backlight flicker

Cheers Tom

I should of said I already changed CM802 when I popped the IC in

The 13v line is down to 11.4v

Will post pictures shortly

Could the F9222l be dodgey and breaking down..yet another ebay best buy

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

Check RM803 is not open/high resistance.

Try attaching a 10 ohm, 15W or higher resistor to 13V line. If the line collapses suspect the F9222L, if not, suspect feedback/optocoupler.

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Re: Samsung LE32R74BDX Backlight flicker

RM803 is reading 0.03ohms, I dont have this 10ohm 15w resistor, I have got a few bad psu's especially vestel ones, is there a resistor on their I can use?

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

Maplin sell something usable

10 ohm 10W ceramic e.g.
http://www.maplin.co.uk/10-watt-wirewound-resistor-2181

but not for too long (max 30 seconds)

Just need to see if power supply rails are stable under load or if there is some problem with them.

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Re: Samsung LE32R74BDX Backlight flicker

Check RM803 is not open/high resistance.

Try attaching a 10 ohm, 15W or higher resistor to 13V line. If the line collapses suspect the F9222L, if not, suspect feedback/optocoupler.

Which optocoupler will it be and can I test that to rule it out before I go and buy the resistor (I live quite far from maplin)

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

There is a reason I suggested the load test because there is no easy way to test the opto.

You may be able to use a car brake light too but you cannot use a car headlamp bulb.

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Re: Samsung LE32R74BDX Backlight flicker

Hi

I have just purchased a 10ohm 11watt resistor, whats the process to check the 13v line, where do I put the resistor

Cheers

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

From 13V to ground. This loads 13V with ~1.3A (if at 13V) and ~1.1A (if at 11V.) The rails should stay steady if it is a problem with feedback, or it will drop if it is a problem with F9222L/current limit/bad output cap.

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Re: Samsung LE32R74BDX Backlight flicker

From 13V to ground. This loads 13V with ~1.3A (if at 13V) and ~1.1A (if at 11V.) The rails should stay steady if it is a problem with feedback, or it will drop if it is a problem with F9222L/current limit/bad output cap.

Do I need to short ps on too..I take it I disconnect the main board and just short 13v

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

Test can be done with main board connected.

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Re: Samsung LE32R74BDX Backlight flicker

Hi

The voltage constantly keeps changing fom 0 upto 17v on the 13v pin

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

What's it do without the resistor?

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Re: Samsung LE32R74BDX Backlight flicker

What's it do without them?

Without the resistor it is now sat at 20.4v

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

On the 13V pin??

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Re: Samsung LE32R74BDX Backlight flicker

Ooops lets start again, I got solder splatter from a diode to the 24v line Luckily got away without a nice pop and more problems, just dicky readings

I will do the test again and report back

[tom66]

Re: Samsung LE32R74BDX Backlight flicker

Gotta make sure main board survived 20V on 13V line!!