Vizio VO47LF 0500-0407-0680 PS board

[tinkerer973]

OK, Here we go. I have a Vizio VO47LFHDTV30A, it went pop and won't turn on. I know PS boards ar common issues with these. I see no bad caps, fuse is good, I have ac power all across the primary side of the board, but once I get to the transformers, I have nothing on the other side.I have some troubleshooting skills, I do radio work once in a while, so I know the basics, but I'm not sure where to start here. I've read a little bit, I have no 5VSB a the output to the main board, thats where I figured I should start. Any help is greatly appreciated.

Tinkerer973

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

Is this the exact match of your board?
If it is, please provide good clear pictures of the bottom side of the board.
http://www.shopjimmy.com/vizio-0500-...wer-supply.htm

What DC Voltage do you have at the two legs of the main filter cap laying on its side in the primary side of the power supply?
Be real careful since you are working in the primary deadly side.

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Yup, that is my exact board, I'll try to get a few pics posted later. I didn't see anything unusual, except one blue cap( tantalum I think)c901 near Q901 has a dark spot under it looks like heat mark to me but could be normal, that and all the really poor soldering, wow, what passes for good these days....anyway across the big cap I have 168vdc, neg. meter lead to chassis pos. meter lead to pos. on the cap I get 94 to 98 vdc varying, neg. meter lead to chassis pos. meter lead to neg. side of cap I get -56vdc. Hope that makes sense.

Thanks, Kevin

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

"anyway across the big cap I have 168vdc, neg. meter lead to chassis pos. meter lead to pos. on the cap I get 94 to 98 vdc varying, neg. meter lead to chassis pos. meter lead to neg. side of cap I get -56vdc. Hope that makes sense."
168VDC at the two legs of the cap is correct, when you make voltage measurement in the PRIMARY (hot side) of the circuit, the circuit ref ground point for the primary is the Negative leg of the main filter cap, you use the chassis as the ground ref when you make the voltage measurement in the secondary (cold side) of the circuit and that is why you get those funny reading of -56, 94~98VDC when you use the chassis as the ground ref for primary side.
The blue cap are CERAMIC HIGH Voltage cap, it looks like it is for the snubber circuit for the standby power supply which we need to fix first. So check the resistance between the two legs of that blue cap, these ceramic cap when it failed, it failed as shorted circuit. There should be a fusible resistor that feed the b+ to the standby power supply section which I cannot locate until I get to see good clear pictures of the bottom side of the board first.

Notes: picture is provided by shopjimmy.

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Ok, resistance across C901 is 1.08K, here's a pic of the bottom of that area, one is pretty clear, the other is a little blurry but of a larger area. Thanks for taking the time to help me out. Kevin

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

I expect higher resistance than that, can you remove the cap and test its resistance off the board?
It is a snubber cap connected in parallel with the Source and Drain pin of the power MOSFET Q901.
You also need to check the fusible resistor R901, it should be < 1 Ohm.
Can you please retake the picture #2? and also the pictures of the whole bottom side of the board?

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Indeed, out of curcuit res is >20M, on 20M setting I still get OL, retest of resistance on the board without C901 installed is 1.100K.

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Aha, R901 is open, with closer inspection I can see a tiny amout of burn on the board under it as well. How I missed that i don't know. Here are some more pics, one is of the whole board the other 4 are kinda quarter shots of the board. along with retake of the 2nd pic

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

You need to remove that 3-pin power MOSFET Q901 mounted on the heat and test resistance between all 3 legs looking at with front side toward you and 3 legs pointed down then check the resistance between
Left (Gate) leg and Middle (Drain) leg = xxx Ohms
Left leg (Gate) and the Right (Source) leg = xxx Ohms
Middle (Drain) leg and Right (Source) = xxx Ohms

That fusible resistor is blown due to shorted (low resistance) some where in the STBY power supply.
BTW, what is the full model number of this VIZIO?

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Gate to drain 1.23K
gate to source 1.8 ohms
drain to source 1.14K

Full model number is vizio VO47L FHDTV30A

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

Gate to drain 1.23K
gate to source 1.8 ohms
drain to source 1.14K

Yes, it is bad and it is more likely that it also damaged that 8-pin SMD SMPS IC, and the components connected between the Gate pin of the MOSFET and the Gate drive pin of the IC.

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

ok, so even though r907,906 and D902 still test good probably replace them and the IC, along with the mosfet, R901 and is C901 still good....am I gonna hurt anything outside of those compents if I replace the Mosfet and the r901 and try it. Can I cause more damage if IC900 is damaged and I dont replace it?

For R901 the fusible resistor, that is about the size of a typical 1/4 watt resistor, thats basicly a flameproof resister of the correct value at 1/4 w , right?

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

If you replace the power MOSFET and the fusible resistor (Flame proof MOX will be OK to use, I cannot tell if it is 1/4 or 1/2W) without replacing the SMPS IC then you can take a chance of damaging the new MOSFET if the Gate drive signal is stuck high instead of switching the MOSFET on and off at 70~110KHz, the MOSFET will be fully on 100% which will be real bad news.
What you can do is to test the power supply board by itself by using 75W in series with the TV so the current will have to flow through the lamp and if the shorts happen, the lamp will light up brightly and stay on bright and limit the current through the TV.
This is what I use:
https://www.badcaps.net/forum/showpo...&postcount=112

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

ok, one more question, then I think I'm off to order parts, Are these PS boards like a computer supply in respect to needing a load to run, will it give me voltage at the main board connector without connnecting it to the main board.

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

Standby is low 5V at 1~2A at the most, the 12V/24V is not tightly regulated but it will come on without the load OK. You can use resistors for light load test. For now we just need to get the standby working first.
You should see 5VSB at the connector the minute you apply 120VAC to the board.
So once you get the STBY to work, then you hook it up to the main board, if the main board is OK then when you hit the power switch, the main board should send the PS_ON (>2.5VDC, this signal is used to turn on the switched transistor to supply the VCC which is generated by the AUX winding of th STBY transformer to run the PFC controller IC and the SMPS IC) to turn on the PFC Voltage booster (the voltage on the cap should go up from 160VDC to >360DVC) and the 12V/24V SMPS section, after slight delayed it should send the BL_ON and diming control signals that are routed through the power supply for clean wiring to the inverter board to turn on the backlights, and at the same time the processor on the main board will send the T-CON on command to turn on the switched MOSFET which is used as a switch to supply the 12V (or 5V depends on the panel) to the T-CON board, that is the basic operation of the TV.

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Sounds good, thanks a ton, we'll see how much the ic is, maybe I'll change it anyway, I just hate SMC so much, lol , my hands aren't as steady as they used to be..... Thanks Again, Have a good evening


Kevin

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

Good luck.

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

Well, parts finally showed up today, Both R901 & R601 got replaced, Mosfet is changed and the C901 High Voltage cap is back in, still no standby power, I'm only getting .20V from the source and gate pins to the Neg. lead of the big cap, with it not turing on, that might be normal, but I think I should be looking at .20v output on more than one leg of the IC inline. I'm thinking the IC is locked open or fried all together. Is it possible that there is no good path to ground so theres no output from the MOSFET? Any thoughts???

[budm]

Re: Vizio VO47LF 0500-0407-0680 PS board

So you did not replace the SMPS IC as I suggested?

[tinkerer973]

Re: Vizio VO47LF 0500-0407-0680 PS board

No, the chip is only $2.80 but the only place I can find it, only ships DHL and they want $27 shipping. If I knew a little about the chip, maybe I could find a suitable repalcement, but I can't find anything on it.... If I'm gonna pay $30 for the chip and shipping, I'm 1/3 of the way to a new PS board already. Any ideas before I order the PS board?