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

[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.

[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.

[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.

[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

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

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

[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

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

Again, how much voltage is on the main filter cap when the tv is on? Measure both leads directly on the cap. Should be more than 360v DC.

[Five_magics]

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

160vdc

[CapLeaker]

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

When the tv is turned on?

[CapLeaker]

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

160v DC is just rectified mains, so either the tv is off, or the PFC (booster circuit) isn't working.

[Five_magics]

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

You actually made me doubt, but the TV is indeed on. Still 160vdc on main caps.

Funny part is, this time, the backlight actually lit up for a few seconds before shutting down. Last thing I did was take measurements (check-diode) in the PFC circuit. Faulty PFC? Thought it could be a bad contact so I tried tapping the board near the PFC but no dice.

Or can a faulty CCFL/inverter shutdown the PFC circuit?

[budm]

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

You can disable the bl-on signal by grounding the bl-on pin. With 100 Ohms resistor to Gnd to see if the PFC will come up and stay up.
Btw, all these time we thought the backlights never did come on per post 3.

[Five_magics]

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

It didn't come on until just now. By "this time" I meant like an hour ago :O. Used check-diode in the PFC circuit, tested the set again to take measurements and to my surprise it came on for a few seconds, which makes me think I charged a capacitor/FET making it work for a brief time -> bad ICP801?

Will try shorting the BL_on signal tomorrow at work (again, lack of equipements/components).

[CapLeaker]

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

Well... if the backlight came on for a brief second, that is a big game changer.

[Five_magics]

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

Didn't have much time over the weekend, but tonight I shorted BL_on to the ground via the 100 ohm resistor, and the PFC circuit comes on (around 450vdc on main caps).

[budm]

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

Didn't have much time over the weekend, but tonight I shorted BL_on to the ground via the 100 ohm resistor, and the PFC circuit comes on (around 450vdc on main caps).

And it stays at that level? If it is really 450VDC between the two legs of the cap then the PFC circuit should shutdown, it has protection not to let the output Voltage goes way beyond 400V. I hope your meter is accurate.
if you look at the spec sheet of the IC, there is explanation on how the IC works including the OVP (Over Voltage Protection), There are two strings of Voltage divider resistor networks for sensing function.
If you look at the bottom side of the board, you will see two set of resistors, each set has a bunch of resistors connected in series to form Voltage divider and feed the IC pins per the spec sheet. so it can be that the value of the resistors have changed so it caused the output Voltage to go too high, I would check out those resistors.

[Five_magics]

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

And it stays at that level? If it is really 450VDC between the two legs of the cap then the PFC circuit should shutdown, it has protection not to let the output Voltage goes way beyond 400V. I hope your meter is accurate.
if you look at the spec sheet of the IC, there is explanation on how the IC works including the OVP (Over Voltage Protection), There are two strings of Voltage divider resistor networks for sensing function.
If you look at the bottom side of the board, you will see two set of resistors, each set has a bunch of resistors connected in series to form Voltage divider and feed the IC pins per the spec sheet. so it can be that the value of the resistors have changed so it caused the output Voltage to go too high, I would check out those resistors.

Meter probably isn't that great, cost me 35$, Mastercraft brand. Will see if I can borrow a Fluke/BK precision from work, just in case.

Initially it measures at 430vdc~, goes up slowly in 1 volts increments. When it reached 450vdc I shut the TV off, because with caps rated at 450 volts... yeah.

I have seen the divider you're talking about. Will check it out and report.

EDIT: Just checked the resistors and I think the meter is crap. The resistors measure somewhat okay in a direction(1,05M instead of 1,2M), but when I reverse the polarity it drops to 800k or so. Will check it out with a Fluke tomorrow.

[CapLeaker]

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

Most of the time the batts are low when the meter shows crap measurements. If you have the biggest MasterCrap DMM that you got on sale for $30, that is actually the best cheapy and decent for the money.