backlight issue Samsung UE32EH5000

[budm]

Re: backlight issue Samsung UE32EH5000

checked those voltages. im now suspecting failed IC ?

Pin 1 - VCC 13v
Pin 12 - ENA 0v
Pin 15 - ADIM 0.8v
Pin 16 - BDIM 0.8v

Are these Voltage tested when the TV is turned on? I do not expect to see boosted Voltage of 182V if ENA (Enable) pin at 0V.

[Mikeyboy2007]

Re: backlight issue Samsung UE32EH5000

tv turned on and LEDs connected Budm

[budm]

Re: backlight issue Samsung UE32EH5000

Hmm that does not make sense since you do have Boosted VoltAge of 182VDC. At this point I would take a chance on replacing that IC because right now that internal MOSFET for the LED current return is not being turned on or the MOSFET has failed.

[dick_barton]

Re: backlight issue Samsung UE32EH5000

ENA needs to be 1.22V or greater to operate and switches off if less than 1.15V

[Mikeyboy2007]

Re: backlight issue Samsung UE32EH5000

ok thanks. would this do ?

[budm]

Re: backlight issue Samsung UE32EH5000

ENA needs to be 1.22V or greater to operate and switches off if less than 1.15V

That is why it does not make sense to me since he is getting the Boosted Voltage without having ENA control, may be it is measurement error.

[Dannyx]

Re: backlight issue Samsung UE32EH5000

checked those voltages. im now suspecting failed IC ?

Pin 1 - VCC 13v
Pin 12 - ENA 0v
Pin 15 - ADIM 0.8v
Pin 16 - BDIM 0.8v

I too get 0v on enable from what I recall, so perhaps you're having the same issue as I do: that 704 FET going bad and pulling down the enable line. After I killed it by forcing 5v on BLU_ON, I now DO get around 3v on BLU_ON and the backlight does come on, but I'm obviously not leaving it like that. The FET is open-circuit now so I think that actually "did it". Although it was not shorted before, it might explain why it smoked when I applied 5v to it...something was not quite right. I'm surprised it didn't smoke earlier when the TV put 5v on it, since that's what the main board does when it turns on to trigger the backlight :| I shall try replacing that first, since it's cheaper and easier than replacing the IC.

[Dannyx]

Re: backlight issue Samsung UE32EH5000

That is why it does not make sense to me since he is getting the Boosted Voltage without having ENA control, may be it is measurement error.

I too get the same 180v output voltage, so I would concur the IC is fine. Something in the "enable" circuit is acting up. Also, how come 180v is not lighting up anything ? My variac lit up the entire TV with around 110v. Is it the current that's too low ?

[budm]

Re: backlight issue Samsung UE32EH5000

I too get the same 180v output voltage, so I would concur the IC is fine. Something in the "enable" circuit is acting up. Also, how come 180v is not lighting up anything ? My variac lit up the entire TV with around 110v. Is it the current that's too low ?

That is because it is either the Internal MOSFET for the Catode LED current return line inside that IC is bad or it is not being driven so the LED will not light up. That is why you cane take a chance replacing the IC and see what happen.
Spec sheet page 11: Analog Dimming ( ADIM, the range is between 0.3~3V, so 0.8V is OK. BDIM (PWM dimming) must be OK otherwise the boost converter will not be working.
Also look at this thread:
https://www.badcaps.net/forum/showth...FAN7340&page=2

Also check the current sensing resistor on pin 8 to make sure it is OK.

[Dannyx]

Re: backlight issue Samsung UE32EH5000

That is because it is either the Internal MOSFET for the Catode LED current return line inside that IC is bad or it is not being driven so the LED will not light up.

Most likely not driven, since the LEDs do light up if I put 5v on the BLU_ON pin of the PSU (at the increased risk of burning something up even more). If I leave it floating (with that SOT-23 transistor now open), it flashes, so would that mean the IC is good ? I ordered one anyhow, but I'll start with replacing the transistor first...I sure hope 704 stands for 2n7002k.

[Dannyx]

Re: backlight issue Samsung UE32EH5000

Ok, replaced the SOT transistor and it's still not working sadly, so that was just a side-effect Another thing I noticed is that the voltage going to the LEDs (the blue wire) is a bit too high: with the LEDs connected, it goes to 230v, whereas those caps are only rated for 200v...should I bother to replace the caps ? Somebody suggested doing so in a local forum...don't know whether it actually fixed anything or not. My buddy could not find the IC at the local "radioshack" so if someone manages to find it and replace it, please at least let me know if it works.

[dick_barton]

Re: backlight issue Samsung UE32EH5000

As a quick test could you just tie the ENA to REF which is at 5V using a 10K resistor without the SOT in circuit and then check the voltages and see if the leds come on

[Dannyx]

Re: backlight issue Samsung UE32EH5000

Here are my readings, with no hacks, no straps and nothing complaining:
ENABLE: 3v
REF: 5v
ADIM: 0.8v
BDIM: 1v
230v on the "send" blue wires, around 130 on the Drain pins of the IC (the "return" black wires). Measurements taken with respect to chassis ground. If I measure across the LED output connector, with negative on black and positive on blue, I get a random reading that jumps around between 0 and 1.4 or thereabouts....Dead FET inside the IC perhaps ? :| Just because the readings are in spec, doesn't mean the IC is fine internally, like BudM suggested.

[dick_barton]

Re: backlight issue Samsung UE32EH5000

If you disconnect the leds do you have an open circuit voltage still of 230V on the blue wire?

What resistance do you read between Pin 8 and ground (Sense resistor)

[Dannyx]

Re: backlight issue Samsung UE32EH5000

If you disconnect the leds do you have an open circuit voltage still of 230V on the blue wire?

What resistance do you read between Pin 8 and ground (Sense resistor)

The sense resistor reads 3.3 ohms which is correct. The voltage at the output is present and identical regardless of whether the LEDs are connected or not: slowly rising to 230v (presumably the PSU is trying to meet the set current by increasing the voltage on the load but stops at an upper threshold). The small connecting cable is OK because I applied power with my variac and the strips came on. I even moved it around when the PSU was plugged in to ensure it wasn't just a one-off occasion where it conducts in one orientation but stops conducting when it's moved or twisted.

[dick_barton]

Re: backlight issue Samsung UE32EH5000

It does make me think that the internal mosfet has failed as Budm has already suggested as a possible cause of the problem.

I haven't done this before so I don't know if it's a good idea but if you quickly short Pins 8 & 9 (shorting the drain/source of the internal mosfet) do the backlights come on?

[thoma]

Re: backlight issue Samsung UE32EH5000

https://www.youtube.com/watch?v=KHBdZqGhMTg[

http://www.berlin-repariert.de/samsu...270-kein-bild/

[Mikeyboy2007]

Re: backlight issue Samsung UE32EH5000

It does make me think that the internal mosfet has failed as Budm has already suggested as a possible cause of the problem.

I haven't done this before so I don't know if it's a good idea but if you quickly short Pins 8 & 9 (shorting the drain/source of the internal mosfet) do the backlights come on?

i will try that and report back. i have ordered a replacement IC also so should be here tomorrow morning.

[Dannyx]

Re: backlight issue Samsung UE32EH5000

i will try that and report back. i have ordered a replacement IC also so should be here tomorrow morning.

Great. I ordered mine too eventually from somewhere else but will have to wait till next week, so please let me know how things go

[Dannyx]

Re: backlight issue Samsung UE32EH5000

Have you made any more progress on this TV ?