Samsung LN40B650T1F won't power on

[truep]

I just got this set and it won't power on. The standby voltage is 5.2V but the label on the power supply says it should be 3V.(error?) The power on signal only goes to .89V when I hit the power switch. I suspect the main board but I am concerned about that 5V where the label says 3V standby. The signal from the switch board to the main board is 3V. I haven't found the manual yet. Anyone have any ideas?

[tom66]

Re: Samsung LN40B650T1F won't power on

Samsungs often have a 5.2V - 5.4V standby rail; 3V is probably a typo or otherwise incorrect.

Would check all LDOs on main board, then switching regulators and diodes.

[truep]

Re: Samsung LN40B650T1F won't power on

Thanks Tom, I'll give it a try. I kind of figured the 5V was correct as it was in the other Samsungs I have worked on. I hope it's just a regulater as these boards are almost impossible to find at a reasonable price.

[truep]

Re: Samsung LN40B650T1F won't power on

I checked the only one I knew was a regulator, the one near the jack board on the left mid upper side. It has 5.2 in and 3.2 out. After a few seconds the 5V (and the 3.2V)drops and then comes back on this happens over and over. The 5v from the power supply is steady. Are there other regulators or do I have a bad processor?

[tom66]

Re: Samsung LN40B650T1F won't power on

Check the device near the HDMI/USB ports. (Is that the one you checked?)

Check the 4R7 inductor; the side closest to the RAM chips (the two black leadless chips) is the output, probably of the range 1.2 - 2.5V.

On the top left corner check the output of the inductor. Not sure what voltage this should measure.

Remove the board and check the bottom there are almost certainly more components there.

[retiredcaps]

Re: Samsung LN40B650T1F won't power on

the label says 3V standby.

It is definitely 5.3V standby. I can see how you could interpret as 3V.

The board is silkscreened like this

5. 3V (note the space)

STBY5. 3V (note the space)

So you could easily think it was STBYS (instead of 5).

[truep]

Re: Samsung LN40B650T1F won't power on

You guys were right about the standby voltage, My eyes aren't what they used to be!!
The voltage on both sides of 4R7 is 1.8 and changes with the regulator 5v going on and off. Tom, the reg. in question was the one near the HDMI/USB ports.
The set has been plugged in for some time now and the chips are getting warm(not hot just so you can tell). I'll check the bottom of the board now.

[truep]

Re: Samsung LN40B650T1F won't power on

I checked the regulators on the back the voltages seemed ok but all were bouncing up and down from high to 0.something is turning them on and off. I have 5V at the connector but without a schematic, I don't know where to look.
Here is a picture of the back.

[truep]

Re: Samsung LN40B650T1F won't power on

No more Ideas? I need to find out why the voltage goes up and down. Does anyone have a schematic or service manual. Electrotanya has it but I can't open anything but the cover page.

[PlainBill]

Re: Samsung LN40B650T1F won't power on

No more Ideas? I need to find out why the voltage goes up and down. Does anyone have a schematic or service manual. Electrotanya has it but I can't open anything but the cover page.

You aren't doing it right; the Elektrotanya site has some obscure quirks. I use the latest FireFox browser.

On the Electrotanya search results, click on the blue down arrow for the manual you are interested in. This opens a second page which has the first page of the manual. To the right of that, about even with the bottom of the manual, you will see a line that says
'This file is downloadable free of charge from the site - processing...'

After about a minute 'processing' disappears, and 'Get Manual' appears one line down. Click on that to download the manual.

PlainBill

[truep]

Re: Samsung LN40B650T1F won't power on

Thanks Plainbill, I'll try it that way. I do use firefox.

[tom66]

Re: Samsung LN40B650T1F won't power on

Can you get hold of or do you have a resistor ranging from 2.2k ohm to 4.7k ohm?

[tom66]

Re: Samsung LN40B650T1F won't power on

Can you get hold of or do you have a resistor ranging from 2.2k - 4.7k?

[truep]

Re: Samsung LN40B650T1F won't power on

I got suspicious that there were voltages on the regulators so I checked the other power supply voltages. The 13 volts and 5v m were coming on but bouncing with the power on signal. the 5v det. and e-pwm were only coming up 1/2 v. The power on is coming up to about 1.3V.
Yes I have a resistor but it looks like the supply is coming on and shutting down over and over again .

[truep]

Re: Samsung LN40B650T1F won't power on

Now the standby power is gone! I'll have to find that now.

[truep]

Re: Samsung LN40B650T1F won't power on

Standby power is back. the manual is useless as it has no schematics. The troubleshooting diagram doesn't match my symptoms. I wonder is the det 5V is an input to the power supply or an output? if it's an input, it looks like a blown main board.

[truep]

Re: Samsung LN40B650T1F won't power on

Anyone have a schematic for the power supply or main board? The problem with the standby was a bad connection when I unplugged the power board.I just don't know what the det 5v and e-pwm are.

[truep]

Re: Samsung LN40B650T1F won't power on

A new main board fixed it!

[tom66]

Re: Samsung LN40B650T1F won't power on

Great! Sometimes a board swap is the best way...

[MEB]

Re: Samsung LN40B650T1F won't power on

A friend at work has this model Samsung and I have been reading all I can. I may never get him to let me at it, but told him I would run the symptoms by you guys. I have not seen the TV but he emailed me a couple pictures. for a few months this single line appeared at the top of the screen just below the bezel. Annoying, but he continued to use. Now after 5-10 minutes of viewing (with the line) the screen turns black. Audio still functions. Changing channels does nothing. If he powers it off and back on, the TV works fine (with the line) for another 5-10 minutes then screen goes black again. I don't suspect the line and the current problem to be related, and if I get to play with it I will submit board photos and such, but wondered if there might be a common failure on these large Samsungs for this symptom. Seems heat related to the layman. Any guesses?