Need help with power supply on 55" TV

[Matt8110]

So, yesterday I got a free 55" Vizio TV. The model number is VF550M. The guy I got it from said it just stopped working a couple days ago. I tried it and I was able to turn it on but there was no picture or sound. So, I took it apart and did some diagnosing and realized I was getting 5v standby power but only 0.6-0.8 volts on the 12 and 24 volt output! That immediately told me it was the power supply. I know a bit about electronics, but I'm not too experienced with power supplies. So I tried looking up basic things that could be wrong and found I either couldn't understand what they were talking about or that wasn't the issue. I was hoping someone on here might be able to help me diagnose and fix this board. I have 2 other power supplies for parts from other TVs with destroyed screens. Besides that the only tools I have are screw drivers, a soldering iron, and a multi-meter. I don't really have money right now to buy a new board so I was hoping I could fix this one. There aren't any noticeably blown capacitors and anything else for that matter. The board looks fine and smells fine. Thank you

[Emu9x]

Re: Need help with power supply on 55" TV

I'd be looking at the transistors, there are usually the problem with psu boards not getting enough power! in my experience if the 3.3v, 5v, 12v and 24v are missing then the transistor if the first thing i check!

[Matt8110]

Re: Need help with power supply on 55" TV

Thank you, how would I go about testing the transistors?

EDIT:
Also, would I be getting some voltage if a transistor was bad?

[Caleb]

Re: Need help with power supply on 55" TV

Standby voltage are created in a separate circuit from the 12 and 24v
found a repair kit for this power supply, looks like it has a common mode of failure and a bunch of parts that go.

Test out these parts on your board

IC601, 651, 800, 801, 901
D806, ZD902
R667, 841, 847, 917
Q601, 602, 651, 652, 808, 809
F1

[Matt8110]

Re: Need help with power supply on 55" TV

Will do. I can test Diodes, Resistors, and Fuses. But I'm still unsure how to test transistors. I've looked online and can't seem to find a straight answer.

[johnboy1313]

Re: Need help with power supply on 55" TV

Are you sure it's the power supply? The signal to turn the PSU on comes from the mainboard.

[Matt8110]

Re: Need help with power supply on 55" TV

Yes, I am sure. The power supply turns on just fine. I have even tried it with nothing plugged into it with a jumper wire from 5v to PSON and I still get less than a volt from the 12 and 24v pins.

[Matt8110]

Re: Need help with power supply on 55" TV

I'm reading 0 ohms accross resistor 667....Is that even possible?!

[CapLeaker]

Re: Need help with power supply on 55" TV

I'm reading 0 ohms accross resistor 667....Is that even possible?!

Anything that raises your eyebrows and you test it in circuit, always test it out of circuit again. There may be something in parallel in circuit that is shorted, like a diode or transistor.

[Matt8110]

Re: Need help with power supply on 55" TV

Anything that raises your eyebrows and you test it in circuit, always test it out of circuit again. There may be something in parallel in circuit that is shorted, like a diode or transistor.

Thank you, I took that one out of circuit and it tested fine. All the others tested fine as well and so did the diodes. I'm not entirely sure how to test the ICs or Transistors at this point, but at this point I'm guessing it's probably a transistor....

[budm]

Re: Need help with power supply on 55" TV

Is this your power supply board?
http://www.shopjimmy.com/vizio-0500-...upply-unit.htm
You need to find out first if you do have PFC Boosted Voltage of >360VDC measured between the two legs of the main filter cap when PS-ON is applied, no boosted Voltage = no 12V/24v.

[Matt8110]

Re: Need help with power supply on 55" TV

Is this your power supply board?
http://www.shopjimmy.com/vizio-0500-...upply-unit.htm
You need to find out first if you do have PFC Boosted Voltage of >360VDC measured between the two legs of the main filter cap when PS-ON is applied, no boosted Voltage = no 12V/24v.

I just tested it. I'm getting a steady 351 volts DC.

[CapLeaker]

Re: Need help with power supply on 55" TV

It's a bit low, but we have seen that before, good news is that the PFC is working!
I don't have a schematic in front of me to see that circuit

[Matt8110]

Re: Need help with power supply on 55" TV

It's a bit low, but we have seen that before, good news is that the PFC is working!
I don't have a schematic in front of me to see that circuit

I could post some pictures if that'd help.

[budm]

Re: Need help with power supply on 55" TV

351VDC is on the low side enough for the 12V/24V SMPS IC protection circuit to lock down the circuit since at lower Voltage it will require more current to maintain the power out of the power supply.
We will need the P/N of the 12V/24V SMPS IC to look up the spec sheet to see how it operates.

[Matt8110]

Re: Need help with power supply on 55" TV

351VDC is on the low side enough for the 12V/24V SMPS IC protection circuit to lock down the circuit since at lower Voltage it will require more current to maintain the power out of the power supply.
We will need the P/N of the 12V/24V SMPS IC to look up the spec sheet to see how it operates.

Would that be on the hot or the cold side?

EDIT: Regardless here is a list of all the ICs I can find on the board.

Top of the board:
-LM293N
-Either 60915LP or G0915LP...
-ice382065p

Bottom of the board:
2 -DLA001D

But as I said, I am getting something out of the 12 and 24 volt outputs....Around 0.8 volts on the 24 and 0.6 on the 12....

[budm]

Re: Need help with power supply on 55" TV

Disconnect the cable to the invereter board to see what will have happen.
0.8V, 0.6V are just stray Voltage readings.

[budm]

Re: Need help with power supply on 55" TV

DLA001D is supposed to be the same as L6599 by ST Micro but I am not 100% sure.
See exaple circuit so you can at least test the VCC pin.
http://www.st.com/web/catalog/sense_...SC354/PF129679

[CapLeaker]

Re: Need help with power supply on 55" TV

I could post some pictures if that'd help.

Hi res pictures can say more than words. So yes... it does help.

[Matt8110]

Re: Need help with power supply on 55" TV

I figured they were stray voltages. I tried it with nothing but the main board plugged in and without it being in the TV at all. And I will test the VCC on that chip when I get the chance, thank you.

EDIT: My phone can only take 5MP pictures, so I'll have to see if I can find one of my cameras, I think one is 10MP or so.