Another Samsung plasma issue - Videokarma.org TV - Video

YamahaFreak · #1 03-09-2021, 12:36 AM

This time I have a PN60F5500 (AF) that came to me with the following symptoms: TV goes through the motions of powering up, but there are no relay clicks or other noise, no power to the panel, and (as far as I can tell) no sound from the speakers. When you press the power button, the front standby LED flashes slowly several times, like it normally would while the set is powering up, then goes out, as it would once the panel comes up. The standby LED illuminates when the remote is pointed at the TV and buttons are pressed, so the TV is 'awake' enough to see the remote. You can power the set off and the power/standby LED comes back on, as it's supposed to when the TV is off. Inside the set, the green LED on the mainboard flashes at a rate of once every 4 or 5 seconds while the power is on. Various research has told me that the problem most likely lies somewhere on the Y-main (Y sustain) board, Samsung part number LJ41-10331A. I have replaced the small 7-pin IC after being told this could be the issue...this did not fix it. (I installed a socket, just in case.) Some threads online state that replacing three ceramic capacitors on the Y board inside the 64-inch version of this TV fixes the problems, but that size TV uses a different Y board than my 60-inch one, and I was unable to find any similar caps on my Y board. Everything inside my TV looks clean and tidy, no bulging caps or burned/smoked parts, blown fuses, etc. I'd love to repair, rather than replace, the Y board (if it's the culprit), since that is of course the most expensive board in the TV. I can of course answer questions and provide detailed photos, if they will help. I invested in a stand for this set already, so really hoping I can fix it!

JohnCT · #2 03-09-2021, 06:30 AM

The first step is to check the VS and VA voltages from the power supply to the sustains. Samsungs usually have marked test points on the power supply. If one or both are missing, do a resistance check to ground on those two lines - they should be essentially open. If you get a low ohm (1-2 ohm) short to ground, disconnect the Y main. If the short goes away, you've got shorted mosfets or igbts on the sustain, and possibly bad buffers as well. If the short remains, do the same with the X main.

There's more, but start there.

John

YamahaFreak · #3 03-09-2021, 09:50 PM

Thanks John, I'll take voltage measurements and get back to you with what I find. I haven't looked at this particular set, but I assume the correct VS and VA voltages are printed on the back of the panel (they usually are).

YamahaFreak · #4 04-05-2021, 05:03 PM

UPDATE

I have replaced the Y-sustain board, and I have one change to report: the panel now flicks on for a fraction of a second upon powering on the TV. No change with repeated power cycles. That Y board cost me quite a bit, so hopefully whatever else is still wrong can be fixed cheaply. I'm sure the panel itself is fine, and the power supply should be okay...mainboard is still flashing the once every four seconds code.

JohnCT · #5 04-05-2021, 05:31 PM

What are you VS and VA voltages, and if they appear, do they stay on or do they decay after a few seconds?

John

YamahaFreak · #6 04-07-2021, 10:42 PM

Quote:

Originally Posted by JohnCT

What are you VS and VA voltages, and if they appear, do they stay on or do they decay after a few seconds?

John

John, thanks for reminding me. Can you refresh my memory as to how to properly take these voltages? I assume there are VS and VA test points, and the negative probe goes somewhere on chassis ground, such as the TV frame. I want to make sure I don't fry the TV, my meter, or myself!

JohnCT · #7 04-08-2021, 06:55 AM

Quote:

Originally Posted by YamahaFreak

John, thanks for reminding me. Can you refresh my memory as to how to properly take these voltages? I assume there are VS and VA test points, and the negative probe goes somewhere on chassis ground, such as the TV frame. I want to make sure I don't fry the TV, my meter, or myself!

You won't damage your meter no matter what you do. The highest voltages on a plasma are below 400V under any condition.

On the power supply, there are test points marked for the VS and VA, which are developed on that board. There are also other voltages that are generated on the sustain boards, but that's farther down the road.

If there are no test points, then use the large harness connectors. The VS will usually have two to four pins all paralleled for current capability and the VA one or two, but the boards are marked for these voltages right at the connector.

For either voltage, you use cold ground as reference, which would be any of the mounting screws (other than upper and lower buffer board mounting screws which might be above ground) or even the entire back side of the plasma display itself.

Other voltages on the sustain boards can be referenced to cold ground or depending on maker, there might be two test points printed on the board to check those voltages.

But for now, our first attack is to see if the power supply is working, so the VS and VA voltages are the first step.

John

YamahaFreak · #8 04-13-2021, 12:38 AM

Quote:

Originally Posted by JohnCT

You won't damage your meter no matter what you do. The highest voltages on a plasma are below 400V under any condition.

On the power supply, there are test points marked for the VS and VA, which are developed on that board. There are also other voltages that are generated on the sustain boards, but that's farther down the road.

If there are no test points, then use the large harness connectors. The VS will usually have two to four pins all paralleled for current capability and the VA one or two, but the boards are marked for these voltages right at the connector.

For either voltage, you use cold ground as reference, which would be any of the mounting screws (other than upper and lower buffer board mounting screws which might be above ground) or even the entire back side of the plasma display itself.

Other voltages on the sustain boards can be referenced to cold ground or depending on maker, there might be two test points printed on the board to check those voltages.

But for now, our first attack is to see if the power supply is working, so the VS and VA voltages are the first step.

John

Hi again John,

I found the measurement process straightforward. Here is what I found.

VS voltage marked on the panel is 208 volts. I measured a high of 463 volts at startup, then it steadily dropped until stabilizing at 23 volts.

VA voltage marked on the panel is 57 volts. I measured a high of 126 volts at startup, dropping to zero after several seconds.

I repeated the measurements a few times...always the same. This, to me, suggests there is a power supply issue.

JohnCT · #9 04-13-2021, 05:00 PM

Quote:

Originally Posted by YamahaFreak

Hi again John,

I found the measurement process straightforward. Here is what I found.

VS voltage marked on the panel is 208 volts. I measured a high of 463 volts at startup, then it steadily dropped until stabilizing at 23 volts.

VA voltage marked on the panel is 57 volts. I measured a high of 126 volts at startup, dropping to zero after several seconds.

I repeated the measurements a few times...always the same. This, to me, suggests there is a power supply issue.

Holy crap, I've never seen one do that. Are you sure about your meter and using the power supply ground screws for ground? These have a hot and cold side so if you're using the heatsinks as ground, be aware that there are one or more on the hot side.

Even when I've seen them overshoot, it's never been more than a few volts as the power supply is very good about watching for overvoltage and snuffing them out quickly.

Also, most VA and VS supplies are separate from each other, so it seems extraordinarily odd that both would not only overshoot, but by so much.

Please don't take this the wrong way, but see if you can verify your meter.

I'll see if I have a power supply for that in the shop. Is there a BN44 number on it?

John