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

[budm]

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

Also make sure PFC diode DP810 is not shorted out.

[budm]

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

BTW, are you sure that those resistors are the correct value as the old ones, since you were getting PFC Voltage before and now you don't after replacing just the resistors.

[Five_magics]

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

Judging from the 7930B datasheets, operating supply voltage should be 13-20v, so at 16v I should expect it to work properly. Could ICP801 be fried?

[Five_magics]

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

Wow ok my mistake, measure with the cold ground as reference, hope I didn't screw anything up. VCC is at 16vdc (was at 12,9v before).

[budm]

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

It has been awhile, see post 22.

[Five_magics]

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

PS_on coming from main board is present, but ICP801 has no Vcc.

[budm]

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

Shorthing the BL_on signal, I'm only getting 160 vdc on the main caps.

EDIT: BL_on is at 5v.

But the PS-ON is present, right? Before your PFC Voltage was over 400VDC, and now you are not getting the Boosted Voltage, so I would check your works and make sure you do have VCC to run the PFC controller IC.

[Five_magics]

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

Shorthing the BL_on signal, I'm only getting 160 vdc on the main caps.

EDIT: BL_on is at 5v.

[budm]

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

What is the boosted Voltage are you getting now?

[Five_magics]

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

Okay received the resistors, swapped them and it's still not working.

[budm]

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

1206 IS 1/4 W.

[Five_magics]

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

They're surface-mounted.

[budm]

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

1/4 W for each of the resistor and they are through hole type?

[Five_magics]

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

Looks like the resistors are 1206 package(0,125in x 0,060in). They're 1,2M and 6,8M. Seems out of luck with Digikey, where else should I look?

EDIT: Found some at Mouser. Will 1/4 watts do? Sounds a bit low to me.

[Five_magics]

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

Until I get the resistors, is there anything else in the PFC I should check out for?

[budm]

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

His problem is that the PFC Voltage booster was over 450VDC which is not normal and caused the circuit to shutdown.

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.

[juliadream]

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

somewhere in this bl feed circuit there will be a very low value resistor.. say 0.5 .. with a couple of traces leading back to the chip which generates the bl_on signal.. check it's value.. it's a current sensing resistor.. if it's gone high then it'll upset everything. I don't happen to have the schematic for this set in front of me.. but from experience with Sammy things.. if it's not the rubbish caps it's the current sensing resistors.. shorting out the bl_on signal is the big clue.. something is up in the monitoring/control circuitry rather than in the output stages themselves..

[budm]

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

You have to measure the Width and Length of the body of the resistor.
https://en.wikipedia.org/wiki/Surface-mount_technology
http://www.topline.tv/SizeChart.html

[Five_magics]

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

Two weeks later, problem came back. Gonna order the resistors and swap them. Anyone can help identifying the P/N or ratings? Gonna order from Digikey.

[Five_magics]

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

TV worked for 4 hours last night. Still working. Will keep testing tonight.

Trouble could have been the other solder joints I remade. The cap at the top had shady looking joints too, the jumpers also.