Vizio VW37 Power Supply PSON working but no 12v or 24v output

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

1) BTW, U302 looks like a voltage regulator. What is the part number?

2) You can test to see if it is shorted in circuit by numbering the pins 1, 2, and 3. Measure the resistance between pins 1-2, 1-3, and 2-3. Any reading under 30 ohms suggests it is shorted and warrants desoldering and verifying out of circuit.

3) Having said that, the voltage regulator may not be shorted, but it may not be outputting the correct voltage. We have seen a lot of cases where the regulator fails to produce the correct voltage. If it fails low, then there probably isn't a lot of collateral damage. If it fails high, it may take out some components.

For example, if an AS1117-33, where the suffix denotes the output voltage, fails high and outputs 4.1V, it could damage sensitive components. If it fails low and outputs 2.9V, then there is probably no damage.

4) On one yet to be repaired main board, I have 2 voltage regulators that are clearly shorted between all pin combinations.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Of course, none of these types of caps have any markings so when I go to replace that shorted cap, I'm going to take replace it size for size off a junk board.

Haha, you answered my question exactly one minute before I even had a chance to ask it.

On top of the .5 ohm resistance, I just checked the capacitance with my fluke 115 and it shows OL.



How reliable would swapping them out size for size be? I bet I have some SMD capacitors sitting around that match up size wise. Would I really just be able to swap them out?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

U302 is 50117B

The resistance readings across all the pins are in the hundreds of ohms.

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

If these are the failed components (or some of them at least), how will I ever be able to know what their intended values were so that I can order replacements?

1) I snuck in post #119 while you were probably posting.

2) C321 and C322 look like the same size as the two suspect ones. Put your Fluke into capacitance measurement mode and measure C321 and C322. I would also measure C323 and C353.

3) C321 and C322 might be in parallel which might give false readings. C323 and C353 might be standalone? Their uF measurements might give a clue as to what C321 and C322 should be.

4) Can you retest D302 to see if it is shorted?

5) RSS065 datasheet is at

http://pdf1.alldatasheet.com/datashe...RSS065N03.html

See if it is shorted between S-G, S-D, and D-G.

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

How reliable would swapping them out size for size be?

Momaka has reported had success replacing size for size. I'll have to search for his posts.

I'm going to do it for my main board, but waiting for my tweezers to arrive from China. I have never soldered anything this small so it will be a challenge for me.

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Would I really just be able to swap them out?

Okay, good thing I bookmarked momaka's posts.

size for size

https://www.badcaps.net/forum/showthread.php?t=12210

more theory of operation

https://www.badcaps.net/forum/showpo...9&postcount=13

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

C321 & 322 are at 4.47 kΩ and 215 μF

C323 is 13 μF and 37.75 kΩ

C353 is 163 μF and 4.434 kΩ

D302 has 302 Ω (really? is that how they do the numbering for diodes?) and 4.431 kΩ reversed.

RSS065 has 10kΩ S-G, 4.422 kΩ S-D, and 11.88 kΩ D-G.

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

D302 has 302 Ω (really? is that how they do the numbering for diodes?) and 4.431 kΩ reversed.

I use the diode test function instead of resistance. Resistance is for older analog multimeters that lacked the diode test function.

A good diode should read between 0.4 and 0.7V one way and 0L the other when the leads are reversed.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

D302 .115v with anode to anode, and .501v reversed

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

C321 & 322 are at 4.47 kΩ and 215 μF

C323 is 13 μF and 37.75 kΩ

C353 is 163 μF and 4.434 kΩ

Hmm, those readings are all over the map and may be influnced by surrounding components or layout.

If you find the datasheet for U301 as momaka describes in the posts that I have linked in post #126, you might be able to deduce the actual cap values from the "typical application or operating circuit".

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

D302 .115v with anode to anode, and .501v reversed

Even though 0.501V isn't 0L, I would say you have a good diode. An obviously shorted diode would be a reading of 0.115V both ways. The low reading again could be due to "in circuit" testing.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I would say (with my limited knowledge) that the low reading is because of the "in circuit" testing, because D90 which is directly connected between the input 12v Vcc and the ground is giving almost the exact same numbers as D302.

Also about the cap numbers being all over the place C323 is distinctly a different color than C332 & C334 (the suspected bad ones). The bad ones look almost identical in color and size to C353, C321, and C322.

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Also about the cap numbers being all over the place C323 is distinctly a different color than C332 & C334 (the suspected bad ones). The bad ones look almost identical in color and size to C353, C321, and C322.

Now that you mention it (which is also a clue I probably need to go to sleep), I can see the color difference in your other photo.

When searching for a replacement, maybe get something in between those two values (163 and 215uF)?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

C353 is stand alone, and C321 & C322 are in parallel with each other. The two failed caps (C332 & C334) are in parallel with each other, so I am guessing their capacitance value would be closer to 215 μF. It might possibly be a bit more since if two 353's were to be put in parallel it would bring it up to slightly over 300 μF.

Would my safest bet be to desolder a working cap (like 353), take some definitive measurements, do a parallel combo calculation, and solder in a ceramic capacitor of known value close to the calculated one?

[retiredcaps]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

The two failed caps (C332 & C334) are in parallel with each other

One other thing I should mention that I thought of while brushing my teeth (and before I saw this post) is that only one cap might be shorted but because they are parallel, it shows up as both being shorted.

If yes, you have a 50/50 chance of desoldering the shorted cap. If that cap is shorted, then do another in circuit reading of the remaining cap to see if it is shorted or not. If not, then you have your uF reading.

There is also a chance that neither cap is shorted and it is something else.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Good call.

I think I will bring the board to school with me tomorrow (in a few hours), and use the equipment there to pull off and test the caps. Their numerous shiny fun toys would be much more suited for the smd work. In the meantime I have to start, create, and finish a presentation for my wireless senior design project, which I am to give in a few hours. I love procrastinating EE homework with EE work done at home.

I will report back later today with my findings.

[PlainBill]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

So I found two capacitors relatively close to the Vin that both have a resistance of .5 ohms. The first photo shows their position relative to where the previously shown portion of this board, and the second photo shows them a bit more clearly. The bottom part of the caps is connected to the ground plane.

If these are the failed components (or some of them at least), how will I ever be able to know what their intended values were so that I can order replacements?

They are in parallel. Remove one and measure it's resistance. If it isn't shorted, measure it's capacitance. If it is, remove the other and measure it's capacitance.

Edit: 'You-know-who' beat me AGAIN!!!

PlainBill

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I brought the board to school with me and used a hot air rework station to pull both caps off. I did a slop-nasty job of it, but in the end got the caps off without damaging anything (picture).

One of the caps is shorted at about 1 ohm. The other capacitor seems to be fine and reads 15-17 μF with a resistance in the 10's of thousands of ohms. With both caps off there is no more short on this portion of the PCB, and the resistance between the traces where the caps were is now something around 4 kΩ (a number I had seen elsewhere on the board and believe to be a good/correct reading).

Do parallel cap pairs usually have the same ratings? Would it be safe to assume that the capacitor that shorted was originally around 16 μF? If this is the case then the pair of them would have been around 30-34 μF - right? If I were to find a single electrolytic capacitor in that range could it work in place of the two smd caps?

[tom66]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I brought the board to school with me and used a hot air rework station to pull both caps off. I did a slop-nasty job of it, but in the end got the caps off without damaging anything (picture).

One of the caps is shorted at about 1 ohm. The other capacitor seems to be fine and reads 15-17 μF with a resistance in the 10's of thousands of ohms. With both caps off there is no more short on this portion of the PCB, and the resistance between the traces where the caps were is now something around 4 kΩ (a number I had seen elsewhere on the board and believe to be a good/correct reading).

Do parallel cap pairs usually have the same ratings? Would it be safe to assume that the capacitor that shorted was originally around 16 μF? If this is the case then the pair of them would have been around 30-34 μF - right? If I were to find a single electrolytic capacitor in that range could it work in place of the two smd caps?

Yep, you've found the fault. You can actually power up the TV now without the failed cap, but the picture will look poor... usually blurry or dim. Still, it will confirm if the rest is working. You are probably looking for an 22uF 16V 1206 ceramic capacitor. Check the voltage across the remaining good cap to find the replacement voltage rating.

You cannot use an electrolytic capacitor. You may be able to get away with a tantalum, but ceramics are cheap and readily available, use them as you can guarantee they'll work.

Something like this: http://parts.digikey.com/1/parts/764...bj226ml-t.html

[budm]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I use electrolytics cap in place of the SMD if you have the room to install the larger size cap. Make sure to use ESR type caps. When I work on T-CON board, I usually leave off the metal cover, it will run cooler and it will allow you to use larger cap.