Samsung LN46D630M3F, TV powers on, sound works but no backlight

[Five_magics]

Hey! So I have this LCD TV (Samsung LN46D630M3F) which is my brother's and needs to be fixed, been out of the troubleshooting world for a while, thought I'd ask here. The set is 5 years old or so.

Basicly, the TV powers on, plays some Samsung tune, and isn't backlit(not even for a second). From what I got told, the TV worked just fine one night, and the next morning it didn't.

Already ordered an inverter board on a whim, until then I'm trying to see if the power supply isn't at fault. Already swapped all electrolytic capacitors, also checked most semi-conductors and they all seem fine (at least none are shorted). When everything's plugged in and TV is powered on, there's a coil whine coming from the power supply unit for half a second then it stops.

Took some voltage readings at the inverter's connector tonight, which are;

LD=10,8v
13v=12,1
CNT_PRT (current protection?)=11,6v
OVP=0v
GND=0v

Also tried powering up the set without the main board connected; backlight lights up for half a second and shuts down. Tried taking readings at the inverter connector with the main board/inverter disconnected, but forgot to take notes. Will do it again tomorrow. Didn't bother taking primary readings at this point.

After a google search, couldn't find the power supply schematic (BN44-00463A), so if anyone has it, that'd help a ton.

Any help is welcome. Thanks!

[RCA2000]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

USUALLY...a BL that "lights for a couple of seconds and then drops...is the fault of the BACKLIGHTS--be they CCFL tubes of LED"S.

Show a rear pix of panel with all boards--and I will get a better idea of things to go on...

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Like I said, with everything plugged in the backlight(CCFL) doesn't even light up. When the main board is disconnected, it lights up for half a second and shuts off.

Will take pictures and post tomorrow.

EDIT: Missed the stickied thread. Sorries!

[CapLeaker]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

probably the inverter board.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Here are pictures of the main board, power supply and inverter board.

Took the power supply to work today to test the ESR of caps. Turns out one of the electrolytic I put in is bad (30 ohms+). Also CM801 gives no reading, wondering if that could have to do with the value? I usually measure capacitors above 1uF. You can also clearly see heat marks near it.

[budm]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

CM801 is part of the main power supply and you are getting the 12V, etc. so that will not be the problem.
You have power supply-inverter transformers driver board (QI802, QI808 are the power MOSFETs for driving the inverter transformers (3) board).
Fuse FS802S for supplying the B+ to the Inverter driver circuit is OK?
You also need to check the cap CI818 (0.47uF) to make sure the capacitance is still within 10%.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

QI802 and QI808 are okay (at least, not shorted). FS802S is good.

Tested CI818's ESR which was fine, gonna check the capacitance tomorrow.

[dick_barton]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Have you measured the primary and secondary sides of the inverter transformers to check that they all have identical readings?

[CapLeaker]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

So what cap was bad on the PSU that you exchanged?
As already been posted before: You have BLon coming from the main board to the PSU? No BLon no backlights.
What DCV do you get on the main filter cap (measure with both leads directly at the cap), should be more than 360V DC. So be careful.

[ReeceyBurger123]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Ahh that's one of them crappy slot in type of inverters. I have had the output connections on them that go to the lamps corrode and not make connection and more. Remove the inverter and inspect the output connections to see if they are worn down. If they are add fresh solder to them, then wick it off and clean the tab with Ipa.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

At work right now, CI818 measures at 452nF. Already measured the impedance of the inverter's transformers and theyre all identical (IIRC 0,8 ohms on primaries, 1,2k ohms on secondaries).

Will check the main filter caps, BLon signal and CCFLs contacts when Im home, gotta get back to work.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

The bad capacitor is the small electrolytic by the main board connector (CI801 I think).

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Checked the inverter/CCFL's contacts, seemed fine. Redone them anyways and didn't fix it.

BLU_on= 5v
Main filtering caps(they're in parallel)=160vdc

Checked SMD transistors; one of them (QI816) connected to the BLU_on signal reads 0,570~ and the other junctions read overload. Unfortunatly I can't for the hell of me read what's on it, if anyone has any idea...

[budm]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

The backlights inverter requires the boosted Voltage from the PFC/Voltage booster circuit to run, the filter caps should have closed to 400VDC when TV is turned on, so we need to check the PFC section next, starting at PFC diode to see if it is shorted or not, check DP810.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

DP810 is good.

[budm]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

BTW, when you check the DCV on the filter, the PS-ON signal is present, right?
The PFC IC is the 8-PIN SMD ICP801, need to get the P/N so you can get the pin out to find out if it is getting the VCC for it to run or not.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Haven't checked those yet. IC is barely readable, all I can see is 903B, 803B, something like that.

By the way, I haven't heard of PFC circuits before (really only repaired computer monitors and SVDU's (IFE display on aircrafts)), so if you have a good read explaining how they work and everything, that'd be much appreciated, so I at least understand what I'm dealing with. Also, if you have the schematic, I'd love having it, or at least a schematic that somewhat looks like it.

[budm]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

http://www.toms-service-manuals.com/...&typekey=0&p=2
tom66 provides lots of free sch.
You can look through some of the PFC Voltage booster circuits.
Or just search for 'pfc boost converter tutorial', or 'power factor correction using boost converter pdf'

Example in the attached PDF.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Pics from the circuit around ICP801.

There's a repair kit on ebay that includes ICP801 for this very board, but the P/N isn't listed -_-. Can't read the IC except for the bottom part (which usually isn't the part number, IIRC). If that can help you guys identify it or at least give you some kind of idea.

PIN 4 and 7 are grounded. At least, PIN 4 goes through a ceramic resistor (0,4 ohms?) straight to the ground(kathode of main filter caps). PIN 7 goes to a diode (which isn't shorted), so either the pins are internally connected or it is shorted.

[RCA2000]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Are you getting boost converter action--when the set is turned on? You will NOT see this in standby. The PFC ckt ONLY operates in the RUN mode--to reduce current flow and (theory--at least) power draw of the power supply. There should be close to 400 V dc on the filter caps in the RUN mode--around 160 or so in standby. 160 is NOT enough...for run...