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Old 01-10-2012, 11:51 AM   #1
RCFLYER
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Question Samsung 50" Plasma, No Picture or sound

I have a Samsung 50" Plasma PN50B450B1A with no picture or sound.
At first when I plugged it in, the red LED on the front of the set will quickly blink twice pause then blink 5 times. Then hear a clicking noise and cycle the
blinking again. Same problem when I replaced the power supply (PSPF520501A), with a new one. Then replaced the signal board (BN94-02841A)
There was an improvement, when pluged in I hear a click and the red LED stays on, then another click no picture or sound still, when power button is depressed it turns off, it clicks and the LED turns on again. Won't stay off.
Can someone tell me what can cause this?
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Old 01-10-2012, 12:21 PM   #2
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Default Re: Samsung 50" Plasma, No Picture or sound

You should start by posting pictures of the inside of your TV.

Many Samsungs have problems when trying to boot with a new main board esp. if the main board was pulled from another TV.

Try mute-menu-power or menu-mute-power (when the TV is off) to enter service mode.
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Old 01-10-2012, 02:33 PM   #3
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Default Re: Samsung 50" Plasma, No Picture or sound

Samsung plasma TV's have version numbers that are CRITICAL when ordering parts. There are I believe14 versions of model PN50B450B1DXZA. The boards may look identical, but are usually not interchangeable. Look for a sticker (much smaller than the main sticker on the rear) on the left side (viewing from the rear) that will have ONLY the model #, Serial # and a version number. The version will be something like SL04, ST10, etc. Post that, as well as the pictures requested by tom66 above.
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Old 01-10-2012, 02:38 PM   #4
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Default Re: Samsung 50" Plasma, No Picture or sound

No luck with the menu ,mute, power input. I'll check the numbers
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Old 01-10-2012, 03:31 PM   #5
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Default Re: Samsung 50" Plasma, No Picture or sound

I'd suggest reinstalling the original main board. Try disconnecting the power cables to the Y-Sustain (from the upper left corner of the power supply) and the X-main (from the middle right side of the power supply) and trying to turn it on. If it turns on and you have sound, the problem board can be identified by reconnecting each of the power cables in turn. (Do this with power OFF!!!)

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Old 01-10-2012, 03:39 PM   #6
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Default Re: Samsung 50" Plasma, No Picture or sound

Quote:
Originally Posted by PlainBill View Post
I'd suggest reinstalling the original main board. Try disconnecting the power cables to the Y-Sustain (from the upper left corner of the power supply) and the X-main (from the middle right side of the power supply) and trying to turn it on. If it turns on and you have sound, the problem board can be identified by reconnecting each of the power cables in turn. (Do this with power OFF!!!)

PlainBill
And let the caps discharge, if you try to connect a sustain while the TV is off and those caps are charged, pop! The capacitors on the sustains charge rapidly. If you're lucky, nothing happens. If you're unlucky, you blow the fuse on the sustain. Give it 30 seconds and it will be fine.

---

I had a 42" Samsung plasma (of the same PNxxB450 model prefix) with a failed Z-sustain and the front LED would blink several times and the TV would click on and off every 5 seconds. Unplugging the Z-sustain made the TV turn on, with no picture but sound.

Last edited by tom66; 01-10-2012 at 03:52 PM..
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Old 01-10-2012, 09:22 PM   #7
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Default Re: Samsung 50" Plasma, No Picture or sound

Quote:
Originally Posted by randtek View Post
Samsung plasma TV's have version numbers that are CRITICAL when ordering parts. There are I believe14 versions of model PN50B450B1DXZA. The boards may look identical, but are usually not interchangeable. Look for a sticker (much smaller than the main sticker on the rear) on the left side (viewing from the rear) that will have ONLY the model #, Serial # and a version number. The version will be something like SL04, ST10, etc. Post that, as well as the pictures requested by tom66 above.
The numbers is S602
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Old 01-11-2012, 09:29 AM   #8
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Default Re: Samsung 50" Plasma, No Picture or sound

Progress I have sound when the right, X main board is plugged in by itself. No sound when the left, Y sustain board is connected.

Last edited by RCFLYER; 01-11-2012 at 10:20 AM..
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Old 01-11-2012, 11:31 AM   #9
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Default Re: Samsung 50" Plasma, No Picture or sound

Quote:
Originally Posted by RCFLYER View Post
Progress I have sound when the right, X main board is plugged in by itself. No sound when the left, Y sustain board is connected.
Replace the Y-main board then.

Use the original main board the TV had, and see if you still have sound.
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Old 01-11-2012, 05:09 PM   #10
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Default Re: Samsung 50" Plasma, No Picture or sound

Original boards were installed when tested.
How much does a Y-main board cost, or can it be repaired? The board is huge, must cost a gazillion dollars.
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Old 01-11-2012, 05:21 PM   #11
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Default Re: Samsung 50" Plasma, No Picture or sound

Quote:
Originally Posted by RCFLYER View Post
Original boards were installed when tested.
How much does a Y-main board cost, or can it be repaired? The board is huge, must cost a gazillion dollars.
These newer Samsung plasmas are putting the buffer ICs on the main board to reduce the cost (except to the consumer when they get the repair bill!) It varies, but you'd probably be looking at from 50 to 100, if you were able to source a tested, working, second hand part.

If you are skilled with a soldering iron and multimeter, it may well be possible to repair it yourself. I have repaired a Panasonic Plasma Y-main (SC board). It had at least three times as many components on it (plus separate buffer boards, instead of buffer chips on the sustain) and was extremely advanced (one of the first 1080p plasmas.) I found a single MOSFET on the power board had failed short circuit, I replaced that and the TV worked beautifully.

Last edited by tom66; 01-11-2012 at 05:28 PM..
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Old 01-11-2012, 06:43 PM   #12
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Default Re: Samsung 50" Plasma, No Picture or sound

Quote:
Originally Posted by RCFLYER View Post
Original boards were installed when tested.
How much does a Y-main board cost, or can it be repaired? The board is huge, must cost a gazillion dollars.
Double check this part number: LJ41-05905A. If it's correct, the board is available for anywhere from $50 to $180.

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Old 01-11-2012, 09:05 PM   #13
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Default Re: Samsung 50" Plasma, No Picture or sound

Is there a way to test the MOSFET's on the board?
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Old 01-12-2012, 01:03 AM   #14
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Default Re: Samsung 50" Plasma, No Picture or sound

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Is there a way to test the MOSFET's on the board?
Yes, with a multimeter, 99% of failed MOSFETs go short circuit.

First post some close up pictures of the board.
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Old 01-12-2012, 08:03 AM   #15
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Default Re: Samsung 50" Plasma, No Picture or sound

In the 4th picture I noticed some discoloration on a heatsink on one of the MOSFET. I don't know if this is normal.
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File Type: jpg 101_6280.jpg (246.0 KB, 174 views)
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Old 01-12-2012, 10:15 AM   #16
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Default Re: Samsung 50" Plasma, No Picture or sound

MOSFETs can get hot. If they run hot for a long time, they develop thermal fatigue, which leads to internal short circuits.

To confirm it is shorted, use the ohmmeter function of your multimeter to probe from both ends of the fuse to an exposed screw hole. If your meter shows less than 100 ohms, I would consider the board shorted, but repairable.

Sometimes, the fuse blows when these boards short, so the TV keeps working. Clearly, that hasn't happened in your case, probably because the power supply is in protection mode with a shorted load. The fuse probably blows in 30% of the cases, I think it's just there to comply with some laws involving high output current/voltage supplies.

Every device bolted to the heatsinks that you see on the board needs to be tested, all six combinations of pins. Test from the bottom of the board.

Last edited by tom66; 01-12-2012 at 10:19 AM..
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Old 01-12-2012, 10:38 AM   #17
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Default Re: Samsung 50" Plasma, No Picture or sound

It measures .3 ohms from screw hole to each side of fuse. Seems there is a short. What reading should I look for when I test the devices bolted to the heatsinks.
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Old 01-12-2012, 11:18 AM   #18
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Default Re: Samsung 50" Plasma, No Picture or sound

Quote:
Originally Posted by RCFLYER View Post
It measures .3 ohms from screw hole to each side of fuse. Seems there is a short. What reading should I look for when I test the devices bolted to the heatsinks.
Good, that's definitely shorted. You should be looking for OL or "1" on all of the devices, except the two legged ones (if any) as these are diodes.
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Old 01-12-2012, 01:03 PM   #19
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Default Re: Samsung 50" Plasma, No Picture or sound

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Good, that's definitely shorted. You should be looking for OL or "1" on all of the devices, except the two legged ones (if any) as these are diodes.
Do I test from screw hole to each pin of Mosfet, or between the pins of the Mosfet themselves.
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Old 01-12-2012, 01:21 PM   #20
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Default Re: Samsung 50" Plasma, No Picture or sound

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Do I test from screw hole to each pin of Mosfet, or between the pins of the Mosfet themselves.
Between each pins. Mentally number each pin 1, 2 and 3. No need to test the screw. Then place the red lead on 1, black lead on 2. Note reading. Place red lead on 2, black lead on 1. And so on, until every combination of pins is tested, for every device. This might take you a while, but the hope is we'll narrow it down to a group of devices that are in parallel. (Then the devices should be removed and individually tested, to determine the failed one, but that's for later.)
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