Samsung UN50H5203 Blinking Standby light

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Diode checks out - Vf = 0.503 V, DC Resistance is 1.52kOhm
beads are shorted.
Capacitor is reading 1.52k Ohm in-circuit (71.86 MegaOhm out of circuit)
98.77 nF out of circuit
and ESR is 5.3 Ohms

there is a blue disk capacitor in the area, C9011. ESR is reading very high in-circuit (close to 1 kOhm), is it worth taking it out of circuit?

[budm]

Re: Samsung UN50H5203 Blinking Standby light

The diode resistance reading 1.5K in both direction off the board?
Your ESR meter is made for lytics caps not for ceramic or poly cap.
the blues disk cap is the snubber cap, it will have leakage resistance when it goes bad.
'Capacitor is reading 1.52k Ohm in-circuit' I wonder where that 1.52K Ohms is coming from, need top trace the circuit at this point.

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Sorry, that's 8k in one direction, and 1.5k in the opposite direction
the 1.5k I measured for capacitor resistance is the same as the diode's.. in parallel it seems. so 1.5k and 8k in opposite direction.

[budm]

Re: Samsung UN50H5203 Blinking Standby light

I draw up the diagram and get some basic idea how it works, that diode D9001C is not really directly in parallel with the cap based on the traces on the board. I expect that diode will have much mush higher resistance than 8K when Red probe of DMM on the Cathode and Black probe is on the Anode. That diode may be bad which may explains why the Voltage on the D is about the same as at D- even when the LED connector is not in place if that diode has bad leakage resistance, you can do the same test with other diode off the board and see what you get. Please also get the P/N of that diode.

BTW, do the backlights even flash on for seconds? I expect that it should at come on since the Voltage feeding the Anode of the LED string is present?
Please also check cap CM862, 863 also.
Please get the P/N of SMD IC 9151 That may give us a clue as how this LED driver circuit work and see if it matches my diagram, it may be AOZ1948A

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Hi budm,
Diode is SF28G. I see it is used elsewhere on the board and yes, you're correct the other diodes are reading much higher value.
I started drawing the diagram, but I couldn't find the datasheet for the transformer next to the LED power connector (SC-04B SC-149REN)

The backlights don't even flash on bootup. very odd.

CM862 &863 seem to check out. Very high DC resistance, 17 uF total (each is labeled as 10 u), and ESR is 2.7 Ohm (a bit high)

IC is labeled:
402
7014x
8607

[budm]

Re: Samsung UN50H5203 Blinking Standby light

I would try replacing that diode.

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Sounds good. I have this diode MR756 handy.. do you think it would do the job for a quick test?

[budm]

Re: Samsung UN50H5203 Blinking Standby light

MR756 is not high speed diode.
https://cdn.badcaps-static.com/pdfs/...75bed37926.pdf

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Thanks.. i threw it on there just for a quick check and the backlight does come on. Rectifier is not fast enough as you stated so the backlight flickers. Will order the correct part. Thank you so much!

[budm]

Re: Samsung UN50H5203 Blinking Standby light

That is good progress!
BTW, take the resistance reading of the new diode too.

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Will do. Thanks again for the help.

[budm]

Re: Samsung UN50H5203 Blinking Standby light

BTW, when you install the new Diode, keep the leads longer so the body of the diode is not touching the board, may be about 1/2" above the board to allow better cooling.

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Thanks. I received the diode and installed it as instructed - works great. Resistance is 3.5 Mega Ohm and 10.4 Mega Ohm in opposite directions.

Thanks again for the help!

[budm]

Re: Samsung UN50H5203 Blinking Standby light

Glad to hear! Thanks for the follow-up.
BTW,
1) So where dis you get the replacement from?
2) What is Voltage on the D - now?

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

Ooops.. Sorry, I put it back together without measuring the D. I bought the diode from Digikey (0.43 cents ) I bought 2, so I have one spare if you need it I can gladly ship it to you.

[budm]

Re: Samsung UN50H5203 Blinking Standby light

You may want to ship it to him:
https://www.badcaps.net/forum/showth...629#post854629

[jason123]

Re: Samsung UN50H5203 Blinking Standby light

In the mail!