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

[Five_magics]

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.

Battery is brand new. https://m.canadiantire.ca/#/products...055&quantity=1

Thats the meter. Says voltmeter but it really is a multimeter.

[Five_magics]

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

Measured the resistors out of circuit and they're good.

[CapLeaker]

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

Yeah... just what I thought. I have that auto ranging one and it is the best cheap multi meter (when it is on sale $30) that money can buy.

http://www.canadiantire.ca/en/pdp/au...l#.VxbKIxb2Ykk

When things measure funny in circuit and you don't have a schematic, always lift a leg or take the component out and measure it again out of circuit.

[Five_magics]

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

Yeah... just what I thought. I have that auto ranging one and it is the best cheap multi meter (when it is on sale $30) that money can buy.

http://www.canadiantire.ca/en/pdp/au...l#.VxbKIxb2Ykk

When things measure funny in circuit and you don't have a schematic, always lift a leg or take the component out and measure it again out of circuit.

Skipped the auto-ranging since I personnaly hate them. Always takes me too long to figure what range Im on.

And yeah I know about in-circuit vs out-circuit, just prefered to wait at work since its SMD and my personal soldering iron suck. Love my Hakko at work, with a JS02 tip. That thing does wonders.

[Five_magics]

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

Well, it looks like I fixed it. As mentionned earlier, took out the resistors to test them out of circuit. They were fine so I soldered them back. Also took the occasion to remake a few solders near the voltage divider, since I had like 5 minutes left to my lunch break.

Came home, plugged it all back in to test it with another DMM, in case mine was inaccurate... main caps had 390vdc . My meter has to be inaccurate. Test with my meter, still 390vdc. Hmmm let's unshort the BL_on signal. Backlight came on and stays on.

The TV has been running for a few minutes now and it's still working. Looks like it was a bad solder. Gonna leave it for a few hours to make sure.

Here's a picture of the solders I remade.

[budm]

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

Glad to hear, it is either bad joints or the value of the those high resistance have changed when heated with soldering iron, or contamination.
Just keep an eye on it.
So both meter show 390VDC?

[Five_magics]

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

Glad to hear, it is either bad joints or the value of the those high resistance have changed when heated with soldering iron, or contamination.
Just keep an eye on it.
So both meter show 390VDC?

Yep both meters gave the same readings (390vdc).

Also If you remember last week, I took readings in the PFC circuit (including these resistors), and after testing it the backlight actually came on for a few seconds, before shutting down.

Will definitly keep an eye on it. Been working for an hour so far.

[CapLeaker]

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

390V DC is perfect, PFC (booster) is working A1. The picture you outlined a few SMD resistors in a string. I don't think that was the cause, that looks too good. Anyway... main thing is the TV is working again.

[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.

[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.

[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

[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

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.

[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?

[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.

[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

They're surface-mounted.

[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

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

[budm]

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

What is the boosted Voltage are you getting now?