Samsung LN-S3251D Black Screen

[PlainBill]

Re: Samsung LN-S3251D Black Screen

Oops.....
Make that 1.5k ohms on the secondary outputs.
The 20-pin IC is a BD9882.

One more thing I forgot - check the fuses.

Does your DMM only read 2 digits?

Look, I'm being serious here. There are a number of causes for the 'two seconds to black' problem. One is a bad CCFL. Another is a transformer with shorted turns. A third is a bad component in the sense circuitry.

Shorted turns often cause a slight change in the resistance of the secondary - anything over 3% is significant. That would be the difference between 1.51K and 1.55K.

Replacing a transformer is a PITA, but it is much easier than identifying which diode, resistor, capacitor or transistor is bad. If you would rather just buy a new inverter, or toss the whole TV, just say so.

PlainBill

[Sam I Am]

Re: Samsung LN-S3251D Black Screen

Oops.....
Make that 1.5k ohms on the secondary outputs.
The 20-pin IC is a BD9882.

[PlainBill]

Re: Samsung LN-S3251D Black Screen

Okay.... here are the pics.
If you need more detail, I will have to redo them as left/right since the board is fairly long.
The first five pins (ribbon conn.) from the left are showing 24V from the PS.
Starting with the first pair of pins on the far left, the secondary side of the inverter transformers are showing 1.5 ohms on all 8 pair without variance.

No they aren't. They might be reading 1.5K ohms, but there is no way the secondaries could be reading 1.5 ohms. Recheck them to the full accuracy of your DMM.

What is the part number of the 20 pin IC in the center of the board?

PlainBill

[Sam I Am]

Re: Samsung LN-S3251D Black Screen

Okay.... here are the pics.
If you need more detail, I will have to redo them as left/right since the board is fairly long.
The first five pins (ribbon conn.) from the left are showing 24V from the PS.
Starting with the first pair of pins on the far left, the secondary side of the inverter transformers are showing 1.5 ohms on all 8 pair without variance.

[PlainBill]

Re: Samsung LN-S3251D Black Screen

most probably a faulty inverter, test the impedances across the pins of the inverters and look for one that doesnt have the same impedance as the rest of the pack (not to say you couldnt have 2 faulty inverters)

A minor detail, but using correct terminology helps avoid confusion. 'Inverter' usually refers to the PC board that provides the high voltage to the CCFLs. You are suggesting he measure the impedance of the inverter transformers. I agree, there is a very good chance that is the problem. Or it could be the inverter controller.

Now to be a real PITA, I'm going to point out that most of us don't have an impedance meter, we have to make do with the ohmmeter function of a DMM. (But an impedance meter would certainly be the best way to test the transformers).

PlainBill

[reidy-]

Re: Samsung LN-S3251D Black Screen

most probably a faulty inverter, test the impedances across the pins of the inverters and look for one that doesnt have the same impedance as the rest of the pack (not to say you couldnt have 2 faulty inverters)

[PlainBill]

Re: Samsung LN-S3251D Black Screen

There is a pin designated B/L ON/OFF on the PS board that connects the ribbon cable to the inverter board.
When the power button is pushed, the voltage reads 4.7V then the backlights flash once. The voltage reading remains unchanged.

Sorry, I should have mentioned one more test. Some of the pins on that connector are probably labeled with a voltage - 24 volts probably. If the voltage doesn't drop when the backlights go off it's either the CCFLs or the inverter. You should know the drill by now. Pictures of the inverter, top and bottom, sharp, as close to 2000 x 2000 pixels as possible.

PlainBill

[Sam I Am]

Re: Samsung LN-S3251D Black Screen

There is a pin designated B/L ON/OFF on the PS board that connects the ribbon cable to the inverter board.
When the power button is pushed, the voltage reads 4.7V then the backlights flash once. The voltage reading remains unchanged.

[PlainBill]

Re: Samsung LN-S3251D Black Screen

This set is a later model (Nov. '06 vs May '06) than the last one y'all helped me diagnose.
When I first got it, powered it up, the chime sounded, the backlights flashed one time, then went black screen.
Opened it up and found about half a dozen broken backlight bulbs. Replaced them with known good bulbs, which was a very tedious process, and fired it back up thinking I had it licked.
So much for that line of reasoning as it still does the same thing, except that all of the backlights now flash once.
Checked all of my voltages and they appear to be within acceptable limits.
I am leaning toward an inverter problem.
Am I on the right track and how do I confirm?

The easy way is to examine the connector to the inverter. With luck the pins are identified. Check the state of the BL_ON pin when the backlights go off. If the voltage doesn't change, it's the inverter.

PlainBill

[Sam I Am]

This set is a later model (Nov. '06 vs May '06) than the last one y'all helped me diagnose.
When I first got it, powered it up, the chime sounded, the backlights flashed one time, then went black screen.
Opened it up and found about half a dozen broken backlight bulbs. Replaced them with known good bulbs, which was a very tedious process, and fired it back up thinking I had it licked.
So much for that line of reasoning as it still does the same thing, except that all of the backlights now flash once.
Checked all of my voltages and they appear to be within acceptable limits.
I am leaning toward an inverter problem.
Am I on the right track and how do I confirm?