Another Samsung plasma issue

[YamahaFreak]

Originally Posted by JohnCT

The wall mounting holes are fine for ground when reading any secondary supply voltage from the power board, but you are measuring DC, not AC.

Even so, those supplies are well bypassed and I'm surprised your meter is giving you those readings on the AC scale. What kind of meter is it?

If your meter has a min/max feature, preset the range for higher voltage and record the max voltage for the VS and VA.

If it doesn't have the min/max, just read the highest value you see before it shuts down.

John

John,

Right, will switch to DC readings. The meter has no min/max function, as it's just a cheapie from Harbor Freight. It's all I have. I will open the set again tonight and get updated readings for you.

[YamahaFreak]

I have new measurements, now that my meter is properly set to DC voltage. On startup, VS voltage briefly peaks at 211 VDC, then drops, at first sharply and then slower and slower until finally settling at 11 VDC after about a minute. VA voltage peaks at 57 VDC at startup, then quickly falls off to zero.

See the attached image for the power supply board part numbers - there are several BN44 numbers.

[JohnCT]

Originally Posted by YamahaFreak

I have new measurements, now that my meter is properly set to DC voltage. On startup, VS voltage briefly peaks at 211 VDC, then drops, at first sharply and then slower and slower until finally settling at 11 VDC after about a minute. VA voltage peaks at 57 VDC at startup, then quickly falls off to zero.

See the attached image for the power supply board part numbers - there are several BN44 numbers.

Those sound about right. Check the panel, there's a sticker that will give you those voltages.

If the 212 is high (I think it's OK), then the power supply will shut itself down. There's generally a VS adjustment on the power supply. You can try moving it a few degrees counter clockwise and see if the voltage matches the label. If it's high, I've found a small value electrolytic up in that area that goes high ESR.

If the voltages are correct, I think you may have a problem at a buffer (cue scary music) that's shutting down the sustain, which tells the control board, which shuts down the power supply.

Before you do, go over the entire surface of the screen with a bright flashlight and look for a teensy tiny bullet type star crack anywhere on the screen. If it has one, it won't be on the outer surface but on the face of the pixels (internal glass). If you find one, or a burned pixel, stop there. The panel is bad and the game is over. If you don't see any cracks or burned pixels, then let's check the scan buffers.

I have a shortcut I came up with to quickly test the scan buffers, but it requires a DMM with a diode scale. I've always used a Fluke for this test but yours should work fine if it has a diode scale.

Flip open any one of the ribbon connectors that connect to the display, and put the negative probe of your meter on *any* of the connections at the connector. The pin spacing is tiny and your meter probe will probably cover at least two, but that's not a problem as we're going to do a batch test of all the output lines of the scan buffer chips on the buffer boards.

So with the meter on diode, and the negative lead on any pin under the ribbon connector, put your positive lead on any of the edge connectors between the scan buffers and the sustain. Move the probe until you get a diode reading (0.6V give or take a tenth). Once you found the right spot, slide the positive probe across all the pins for each of the ribbon connectors. Do this slowly and keep an eye on the meter. If the indicated voltage on the meter drops to zero, there's a shorted scan line on the output side of the buffer. A single scan line will shut the whole shooting match (East Coast expression) down. My experience is that when I find one bad scan line, there's close to a dozen more. All of them coming from the same buffer IC.

If you find that as you move to another connector the meter voltage goes high, move your negative lead until you once again are reading a junction in circuit (0.6v).

If all lines test clear, then you may have a bad Y main (sustain), X main, control board, or main.

John

[YamahaFreak]

I will try and perform your suggested tests tomorrow evening. In the meantime, would it be safe to assume the panel itself is okay if it does illuminate for a brief moment upon each startup cycle?

[JohnCT]

Originally Posted by YamahaFreak

I will try and perform your suggested tests tomorrow evening. In the meantime, would it be safe to assume the panel itself is okay if it does illuminate for a brief moment upon each startup cycle?

I would say yes, particularly if there are no star cracks or blackened pixels on the screen.

John

[YamahaFreak]

Ladies and gentlemen, we have a picture!! I feel really dumb...at some point, when I had the set apart, I must have forgotten to reconnect one of the right side buffer ribbons (see second pic)...as soon as I saw this error, I reconnected it and the set fired right up on the next try. (To be clear, this is after replacing the Y-sustain board.) The picture is still really dim to my eyes...maybe it's the picture controls. The bulk of my issues seem to be over! (EDIT: selecting the 'Dynamic' picture preset brightened things up quite a bit.)

[JohnCT]

Originally Posted by YamahaFreak

Ladies and gentlemen, we have a picture!! I feel really dumb...at some point, when I had the set apart, I must have forgotten to reconnect one of the right side buffer ribbons (see second pic)...as soon as I saw this error, I reconnected it and the set fired right up on the next try. (To be clear, this is after replacing the Y-sustain board.) The picture is still really dim to my eyes...maybe it's the picture controls. The bulk of my issues seem to be over! (EDIT: selecting the 'Dynamic' picture preset brightened things up quite a bit.)

You'd be surprised how often that happens to seasoned technicians. No shame there. Fortunately, you didn't cause a problem. There were certain LGs that would destroy the display if ribbons were removed from the Y buffers. Happened to me, but that was during an intentional disconnect to check for panel loading. The panel was good before I got to it, but the loud cracking noise after disconnecting a buffer told me otherwise. Weeks later, the LG field rep issued a warning at a seminar about this. Too late.

As far as the picture, these later generation Samsung plasmas were not particularly bright. Early Samsungs were stunningly bright, but they suffered more screen burn, more energy usage, and a fairly high rate of buffer and sustain failures from all the power they were running. Those TVs would warm the room when running. You could literally feel the heat if your face was within two feet of them.

In a darkened room (normal viewing really), these have a fairly accurate picture and better black level than most LED TVs that don't use local dimming. Most people have gotten used to LED TVs being cranking to cartoonishly inaccurate images. A display should only be as bright as what we see with our eyes.

John