Vizio vx42l hdtv10a Bad 5VSB Circuit

[jonpad01]

Part # on the board is DPS-283BP B Rev S0

I got this tv recently and have been doing a bit of troubleshooting, but not much luck. I figured I'd make a post here to confirm my theory and to see if anything jumps out that I don't know about.

Here are the symptoms:

-No power, no orange light

-Power button does nothing

-5VSB circuit reads 1.2v initially then slowly climbs to 3 volts, all the while fluctuating +/- 0.25v

-All of the capacitors on the secondary, including the 5v line read at or slightly above their rated capacitance ratings.

-Tested the diode array, the ones just after the secondary from the transformers, they all read about 600 ohms.

-Checked the fuse, 0 ohms.

-I have not checked anything to do with the SMD components

-Replaced the power mosfets just because I didn't have much to go on

-When I jump the 5VSB to PS_On, The relay clicks on/off repeatedly. When I jump it with batteries, it stays on but I only read about 0.1v on the 12 and 24 volt lines. I replaced the relay just because.

I re-soldered everything attached to the heat sinks, the transformers, and the inductors. I did re-solder some SMD components that looked pretty goobered.

-There is no physical damage to the board that I can tell, pics included.

My theory is that the 5VSB line is not working properly, and something along the 5VSB circuit has a bad connection, but I can't for the life of me find it.

Also if anyone can find me a circuit diagram or manual on this thing that would be awesome.

[budm]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Did you check startup/running cap C902 in the primary side next to the stby SMPS IC with small heatsink on top?

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Yes sir I did, it was good according to my capacitance meter. I think tomorrow I am going to pull all of the heat sinks back off and check the resistors / diodes.

I should probably mention that all of this testing has been done off the TV with nothing else connected to the power supply. I noticed when I connected it to the mainboard the 5v line dropped down to 1 volt.

I might also replace all of the electrolytics just because, would there be any reason to think they are bad? I honestly sounds like a capacitor problem to me but they all check out.

[budm]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Yes sir I did, it was good according to my capacitance meter. I think tomorrow I am going to pull all of the heat sinks back off and check the resistors / diodes.

I should probably mention that all of this testing has been done off the TV with nothing else connected to the power supply. I noticed when I connected it to the mainboard the 5v line dropped down to 1 volt.

I would replace it since unless you can verify its ESR.
Testing the board by itself is fine since we are dealing with just the standby power supply only. You can use 27~47 Ohms 1W for simulating the light load on the 5VSTBY output for now. You can also try heating up that cap with hair dryer to see if the Voltage will stay at 5V with resistor load.

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Well I tried the hot air gun(don't have a hair dryer) and got it to go up to about 3.5v, it seemed to be the area around the 2 electrolytic caps for the 5v line.

Just so I understand whats going on here, is the heating a test for bad capacitors? Or does it test for other components as well.

[ammarben]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

the heating is a test for bad capacitors

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Just ordered a round of new caps. I went with Panasonic FM/FC series, they seem to be reputable for low impedance capacitors.

After researching a bit, I realized that capacitor impedance ratings vary depending on what temperature they are at, it's all starting to make sense.

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Well, after installing all new electrolytic caps, I still have the exact same problem. I am reaching the end of my diagnostic ability for power supplies. At this point I'm just guessing at what to replace, does anyone else have any ideas?

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

So I'm back at it. I decided to measure the output on the transformer output, and got nothing, I only get voltage after the diode.

What was interesting tho was when I busted out my analogue meter, it showed that 5v output was hitting 6 volts, and jumping to 7 volts every 2-3 seconds. But I still couldn't get anything off the transformer with it, even when I connected it back up to the mainboard.

Note here, this definitely is the 5v transformer, it was also receiving about 160v from the primary side. Is there any way to test this transformer for sure? The primary side get 0-20k ish ohms resistance depending on which terminals :I test ( 4 of em) and the secondary gets 0 ohms resistance on the 2 pins that are used. I have not pulled this from the board to test it, however.

With the mainboard connected, the 5v output was showing 3 volts, and jumping to 4 volts every 2-3 seconds. Safe to assume the power supply is OK?

I still get relay clicking if i just try to jump to the on switch with the 5 volt line.

[budm]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

"So I'm back at it. I decided to measure the output on the transformer output, and got nothing, I only get voltage after the diode. " Your AC Voltage meter does not have the bandwidth to measure high frequency AC Voltage at 70~100KHz range.
I would try using 47 Ohms 1W to simulate about 100mA of load current as the load without any other board connected to the power supply, it should be able to maintain steady 5V, if it does then add another 47 Ohms in parallel to simulate about 200mA of current and see if the 5V is steady at 5V.

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Okay I gave it a try, I put a resistor between 5VSB and SGND, hopefully that is correct.

33 ohm 1/2 watt Ressitor - between 0 and 1 volt

150 ohm 1 watt Resistor - between 0 and 2 volts

2x 150 ohm resistor - 0 and 1 volt

2x 33 ohm resistor - 0 and .5 volt

nothing connected - 7 - 7.75 volt

All of this was done on my analogue meter, I am going to upload a video of what its doing, because it's hard to explain.

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

https://www.youtube.com/watch?v=DmlG...ature=youtu.be

My phone is clearly really bad quality, or I just don't know how to focus, but basically at the beginning the max voltage is 1 volt, and half way through I disconnected the resistor, it eventually reached 7 volts at the end.

Also, I can buy a 47 Ohm 1W resistor if the ones I'm using aren't correct for testing loads.

[jonpad01]

Re: Vizio vx42l hdtv10a Bad 5VSB Circuit

Guys, break out the confetti, I think I got it working again. I went and ordered the works, two replacement ICs, the startup transistor(Q901), and a triode for the 5v line.

Replaced the transistor, tested, didn't work, replace the triode(D951) Moar volts!

I lost a voltage regulator I pulled from the main board (U33) so I can't do a power on test yet, but I'm confident....

Whats strange is I tested that triode, it measured 300 ohms on each post, and in the correct directions, so I assumed it was OK