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

[Five_magics]

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

So I'm guessing either the PFC circuit is faulty somehow, or there's some sort of feedback and it's in protect-mode?

[CapLeaker]

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

So the PFC controller has enough voltage to be enabled.

[Five_magics]

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

PS_on=4,9vdc
ICP801's VCC=12,9vdc

[budm]

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

FAN7930B spec.
So I am correct based on board tracing that pin 8 is the VCC pin.

[Five_magics]

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

Oh yeah ok I thought you meant on the IC itself, will report back.

[budm]

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

The IC appears to be a FAN7930B.

On which pin would I measure the PS_on signal? Im guessing ZCD.

I take voltage measurements when the set is turned on.

CN802 pin 18 per chart printed on the board.
The exposed pins of the CN802 as you can see from the top are the ODD NUMBER PINS.

[budm]

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

Tracing out the board, pin 8 is the switched VCC pin which gets the VCC through a switched Transistor QM804 (turned on by OPTO PCM802, PCM802 is turned on by the PS-ON) from the AUX winding of the STBY transformer.
So check the VCC on pin 8 with ref to the negative leg of the main filter cap when you turn on the TV and PS-ON is present.

Pictures provided by shopjimmy.

[Five_magics]

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

The IC appears to be a FAN7930B.

On which pin would I measure the PS_on signal? Im guessing ZCD.

I take voltage measurements when the set is turned on.

[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...

[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.

[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

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

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

DP810 is good.

[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

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...

[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

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.

[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.

[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.