Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed but.

[richardjefferson]

Please forgive me if this should have been posted to an existing thread but symptoms are different than what i could find in threads already listed.

Tv started to shut itself off the turn back on. Frequency of events became greater over a month period and eventually it would not turn on at all and the power on light did not come on either.

I replaced 3 bad caps and a questionable one on the power board.
This solved the problem.. for 2 days. the symptoms started again and this time within 4 days the tv would not power up at all.

I have rechecked the board and can not see any visibly damaged CAPs.
When i hit the power button, i hear a click (like a relay) and a light hum (like a transformer) but it only lasts for a couple of seconds.

I did check all replaceable fuses on power board and sub board.

Ok, Volt meter check.. there is power to the board from the sub power board.

On the power board there is an 11 pin connector.
Pin marked A12V/AC-DET reads about 3v
Pin marked PS-ON reads about 5v
Pins marked D5V on any of the connectors carry mimimal (milli volts)

I'm torn with what to try next:
1. pull all CAPs and test them with my Multimeter (Craftsman 82344 Autoranging) and replace any questionable ones. I have not tested CAP's before with the meter.
2. Pull all CAP's and replace them with out testing
3. Buy a rebuilt power board
4. keep researching for another solution.

I don't have the competency level i would like to when reading electrical schematics. im concerned about my ability to diagnose a more complex repair

I found schematics online for the Sanyo boards but not for the samsung power board.

I'd appreciate any thoughts or tips from the members of this forum.
Thanks
Rick.

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Update - I just ordered a replacement power board. a tech had me test the voltage on the pins marked Vs that go to the X and Y sustain boards. With the TV plugged in they topped out at about 1.6V on both connectors. When i hit the power button, they jumped to 208V and held. He told me it was the board that needed to be replaced.

I asked about replacing all the CAPs but he said that the damage would have already been done to the board and replacing the CAP's would not help.

Ill update this thread when the new board comes in and is installed.

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

The tech appears to be incorrect. If the power board is putting out 208V, it is likely working...

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Hi Tom, you are correct. Got the replacement board in on Monday and installed it Monday night and tv did not power up at all although the voltage reading on the Vs pins was a bit higher (5v).

Kids were dissapointed. they dont watch much tv but have been unable to use the Wii since thanksgiving when the problem started.

Any ideas?

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Vs and Va are present right?

Are the main power voltages present when in the fault condition?

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

yes, Vs and Va (looks like Vg to me.. cant find my magnifying glass! )

I just reinstalled the old board and tested it. There is a three pin connector from the power board to the stand by supply board (on/off button). One of the pins is for 5VD. there is only milli volts coming off of that pin

It still turns on once in a while when i push the power button. It did turn on for me just now and when i plugged in the X and Y sustain boards, i did get power to the plasma and speakers (its not plugged into the cable box so only static on the screen).

It stayed on less then a minute then turned itself off. the standby light went from green to nothing.

Regarding power voltages, there is a subpower board that the ac from the wall goes into. there is then a connector from that board to the power supply board. There is 120v present on the connector pins going to the main power board at all times the TV is plugged into an AC Socket.

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Check the Vs and Va when the TV shuts off.

Do you hear a click from a relay when the unit shuts down?

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Now that Ive found my magnifying glass, let me correct my earlier information.
On the X and Y sustain boards there are Vs, Grd, & Vg pins

On the 3 pin connector from the power supply board, there are 3 pins. Va, Grd, D5V.
This is the only connector on the board where i found a pin marked Va.

With the TV on and the cable disconected from that connector, i get the following readings: Va pin - 63 V dc, D5V pin - 5V dc

When the TV turns itself off the power on the Va pin drops quickly, you can watch the meter display continually changing. after about 30 seconds it gets down to the mV range and continues to drop to about 140 mV. The D5v pin drops to about 10mV

Oh, Regarding clicks.
I hear a relay click when it turns on and when it turns off.
I also hear what sounds like the transformer powering up (high pitch) then powering down when it shuts off.

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Oh, Regarding clicks.
I hear a relay click when it turns on and when it turns off.
I also hear what sounds like the transformer powering up (high pitch) then powering down when it shuts off.

sorry for the duplicate info. i saw i could edit the previous post to add this but cant figure out how to delete this post.

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Does PSON change when it clicks off?

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

i found 2 connectors with PS-ON pins. with the power off one reads 5.18V and the other 4.75V. Voltage is not fluxuating.

With power on, the pin that was at 4.75 drops to 124 mV. When i tested it with the 3 pin connector attached the voltage dropped to 1 mV with the tv powered on The green indicator light seems to be staying on but there is no sound or static on the plasma.

I cannot power on the TV with the other connector disconected that has the PS-ON pin carrying the 5.18V

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

You don't need to disconnect the connector to test it while the set shuts down. Just press the meter probe on the metal around the edge of the pin. While it's running, measure the voltage. When it shuts down, see if it changes. If it does, suspect the main board. If it doesn't, suspect the power supply. Since you have replaced the power supply I think your main board is the problem, or something connected to it, such as the side buttons. (Sometimes the buttons get stuck or get contamination inside which makes them contact when they shouldn't.)

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Thanks for the testing tip!

For clarification I have been giving you the readings from the original board, the one i replaced caps on that worked fine for a couple of days. i am sending the replacement board back. it did not work either.

Im checking the PS-ON pin again with all cables plugged in and tv on. The TV decided not to turn off as quickly so im waiting. Its reading 31.5 mV while on. When I push the button to turn the TV off, it jumps to 5.18V.

Am I to get a reading on this pin when the TV turns off by itself? Would i expect this reading to be different then turning the tv off by pushing the power button?

The connector im on has the following pins:
DV5, GND, D3V3, D3V3, GND, GND, A12V/AC-DET, PS-ON, GND, 5vsb, THEM-DET.

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

an hour later and the TV has not turned itself off

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Well, damn, you need it to go wrong before you can diagnose it. Could have been a loose connector that you reseated.

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

I know.. this is frustrating. ive got a vehicle with a problem that only occurs when its not at the shop! The TV is still on (more then 12 hours).

After i replaced the CAPs it went 2 days befroe any problems started to occure.

Im thinking of taking the control board out on the side and making sure that area is clean and free of dust. i did have that off when i first took the tv apart and its tricky to get back into place so perhaps i messed something up there.

Just to clarify your earlier diagnostic tip: "While it's running, measure the voltage. When it shuts down, see if it changes." does this shut down refer only to when the TV shuts itself down or when i turn it off with the power button or both?

I Appreciate all of your help! Thank you for following this.

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Here We Go Again......

I Put the back on, got the neighbor to help me hang it back up on the wall and turned it on.. 2 min. later, it shut itself off.

Ive been able to turn it on about 6 times this evening and each time it shuts down within 60 seconds. it takes about 15 seconds to get picture. on one attempt, the sound did not come on for about 30 seconds (it shut off in 60 seconds)

Any ideas?

[tom66]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

You need to check the PSON voltage when the TV shuts itself off uncontrollably.

The fact that moving it altered behaviour makes me consider a bad solder joint or loose connector.

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

The TV is still on the wall but and would not power up all day. pushing the power button does nothing. Im waiting for help to get it down so i can get into it again and see if there is any change in behavior when its moved.

It seemed to stay powered on in shorter intervals each time until finally it would not turn on at all. this is the same pattern as before.

Ill keep ya updated

[richardjefferson]

Re: Sanyo DP50747-00 (Samsung Power Board LJ44-00132A) - Thought i had problem fixed

Tom, I hope you had a good holiday and are still following this thread.
The TV would not power up while on the wall the past 4 days. When i took it down and laid it flat, it would power up and shut off as before.
I just got the back off and put the meter to the ps-on pin
When tv is on, im getting 113.6 mV and that climbed to aout 114.3 mV then TV shut itself off. When it shut off, the voltage spiked (first reading i could see was 2V and it rapidly dropped into the mV range, then it turned itself back on and i could hear the relays click. after another min, it turned itself off again and i could see the voltage reading spike , the first reading i could catch was 1V and dropped into the mV range over a few seconds. It then bounced back to 4.21V. The tv did not turn itself back on.
after typing above i went back over to the TV to test again. the resting voltage is still 4.21 V. when turning the tv on, voltage is about 113.6 mV. turned off in less then 1 min. i think i saw 2.7 V then dropped rapidly. Took about 5 seconds to get into the mV range and continued to drop to the double digits in mV. after about 60 seconds, it jumped to the 4.21 V again.
I did test by turning the set off by the button. in this case the tv jumps from the 113.6mV to the 4.21V immediatly.

your diagnostic expertise is appreciated.
Thanks
Rick