Vizio VP50HDTV20A Plasma cycles on and off

[cliff_hootarski]

This tv started out as symptoms of a leaky cap. TV would turn off, front LED would go from green to off and then after a while it would turn back on.

I pulled the back off of the tv and inspected the power supply. I pulled all of the filter caps off the secondary side of the power supply and measured them on a Peak Atlas ESR70. All caps, except one measured within tolerance.
The power supply has all Samxon caps (series GF). I R&R'd that cap with a chemi-con series KY(same capacity,same voltage,also measured good with said meter).

After powerup, I got a good picture with sound, however the sound had a definite buzz in it.

After about 45 seconds the tv shutdown. Now the symptoms are a dead tv, no lights(no power LED), no action whatsoever. No relays click.

I double and triple checked to make sure I got the caps back in the right places and correct polarity.

I have the PS on my workbench. No DC voltage on the main primary side filter caps. I assume I need to jumper the relays to get power going to the primary side transformer and switching MOSFET.

Any help pointing me in the right direction would be greatly appreciated.

[retiredcaps]

Re: Vizio VP50HDTV20A Plasma cycles on and off

Any help pointing me in the right direction would be greatly appreciated.

1) Check if you have 5V standby?

2) If yes, check every voltage regulator on the main board. Some Vizio LCD models have problems with the regulators. In particular pcb location U33 seems to be popular. The regulator may have a part number like AS1117-33 where the suffix tells you the correct output voltage (3.3V in this example).

Yes, I know this is plasma, but it is quick to check all the regulators.

[PlainBill]

Re: Vizio VP50HDTV20A Plasma cycles on and off

This tv started out as symptoms of a leaky cap. TV would turn off, front LED would go from green to off and then after a while it would turn back on.

I pulled the back off of the tv and inspected the power supply. I pulled all of the filter caps off the secondary side of the power supply and measured them on a Peak Atlas ESR70. All caps, except one measured within tolerance.
The power supply has all Samxon caps (series GF). I R&R'd that cap with a chemi-con series KY(same capacity,same voltage,also measured good with said meter).

After powerup, I got a good picture with sound, however the sound had a definite buzz in it.

After about 45 seconds the tv shutdown. Now the symptoms are a dead tv, no lights(no power LED), no action whatsoever. No relays click.

I double and triple checked to make sure I got the caps back in the right places and correct polarity.

I have the PS on my workbench. No DC voltage on the main primary side filter caps. I assume I need to jumper the relays to get power going to the primary side transformer and switching MOSFET.

Any help pointing me in the right direction would be greatly appreciated.

I hate it when the picture gets cropped so the edge of the board is lost. It CAN make things difficult.

Two multi-colored cables run from the lower left side of the power supply to the main board. The legends for those cables are obscured. You are looking for a 5V_SB or similar label. Check the voltage on that pin, using a mounting screw as Gnd. If it reads about 5.2Volts, the problem may be on the main board. If it reads 0 volts the problem is on the power supply.

I'd give you other points to check, but the right side and lower edge are missing!!!

Rats!! Retiredcaps beat me to it.

PlainBill

[cliff_hootarski]

Re: Vizio VP50HDTV20A Plasma cycles on and off

The TV would power up and work normally for anywhere from just a few minutes to close to an hour before it would shut down. I don't understand why R&Ring the bulged cap would introduce an alltogether different symptom.

No 5v stby, when I plug in the pwr supply in stand alone mode on my workbench or when installed in the TV. Neither of the two relays click allowing AC to get to the main full-wave bridge rectifiers.

Am I wrong in assuming these rectifiers need AC going to them to get 5v stby? Do i need a signal from the main board just to get 5v stby?

[PlainBill]

Re: Vizio VP50HDTV20A Plasma cycles on and off

No. The main board uses 5V standby to generate the control signals. Verify you are getting DC voltage on the two very large caps.

PlainBill

[cliff_hootarski]

Re: Vizio VP50HDTV20A Plasma cycles on and off

I found by flexing the pwr supply board, the 5v stby comes and goes.
I guess I'm looking for a bad solder joint or broken circuit board track.
This board is really flimsy and flexy!

[cliff_hootarski]

Re: Vizio VP50HDTV20A Plasma cycles on and off

Reflowed a few joints near one of the heatsinks with at least two power mosfets, and the tv is on now. I'll be leaving it on for a few hours and turning it off and on to see if it's fixed.

I did notice the Ysus board has a high pitched buzz coming from it. Any thoughts on that as normal or not?

[tom66]

Re: Vizio VP50HDTV20A Plasma cycles on and off

Reflowed a few joints near one of the heatsinks with at least two power mosfets, and the tv is on now. I'll be leaving it on for a few hours and turning it off and on to see if it's fixed.

I did notice the Ysus board has a high pitched buzz coming from it. Any thoughts on that as normal or not?

Most sustain boards buzz when working.

If the buzzing stops when the picture goes, you might have a problem with the power supply to the sustains.

If the Z-sustain doesn't go off (still buzzing) when this happens, then it's probably the Y-sustain at fault.

[CoppellTVRepair]

Re: Vizio VP50HDTV20A Plasma cycles on and off

As I've written in another thread on AVS the two most common failures in this TV are in the Y-Main/buffers trio and the power supply board.

You can test the power supply independantly by shorting PS-ON and GND on the CN8003 connector at the left side of the power supply.

Make sure there is nothing but AC connected to the PSU before doing so!

Once the board clicks on and stays on you know that most of it is working fine and you go to the second stage where you need to jump VS-ON to D5V on CN8002.

If the PSU is still on then you should be able to measure Vs to GND on CN8006 and if it's there then your power supply is most likely good.

If the PSU fails to stay on then it probably has a problem.

Here's a link to an article describing the process, only for a different board...you can apply it to LJ44-00132A /B with the same success:

http://blog.coppelltvrepair.com/2014...0162a-and.html

Here's a link to a diangostic and repair service for the Y-Main (testing the two buffers is free, but new buffers cost!):

http://www.coppelltvrepair.com/p/805...n-board-repair

And finally here's a link for repairing the power supply:
http://www.coppelltvrepair.com/p/832...-on-and-off-tv


Hope this helps!

[Shinju]

Re: Vizio VP50HDTV20A Plasma cycles on and off

Seems this unit and the VP50HDTV10a are pretty unreliable. the 10A I have started out with Cap issues replaced 10 of them that were visibly leaking, while I hear the Y-Z buzzing I get no picture or sound.