Vizio E550i-B2 no power, no sound, no LED -- blown IC found

[aecune]

Power board model: 056.04167.1071

My TV had an issue six months where it had no picture, no sound, yet a picture could be seen using a flashlight. I was able to resolve this common problem simply by re-soldering (apparently its a problem documented on this forum too: https://www.badcaps.net/forum/showth...50I#post872360)

My current problem is different, as the power LED won't turn on, so I opened up the TV and examined the components.

I found that IC901 has exploded. Another badcaps user reported the same issue. Identical damage, older different TV model (but the board looks identical--probably is identical): https://www.badcaps.net/forum/showthread.php?t=70423

In that thread, a user was able to find the IC's P/N (LD7913JGM6) and datasheet.

Before I replace IC901, I'm concerned that something upstream (a resistor?) is the root cause, and allowed too much current through. However, I can't find a datasheet for the board so I'm not sure how users in the other thread were so easily able to identify what components were upstream.

Can someone help me identify where to look next, or do users here recommend I replace the IC and go from there?

(from other thread) R915: 4.8 Ohms

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

Are you sure it's IC903? or is it IC 901? I would replace C904B & C907 just as a precaution.

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

Are you sure it's IC903? or is it IC 901? I would replace C904B & C907 just as a precaution.

Hi R_J. Not sure where 903 came in. You are correct, it is IC 901! Edited original post to reflect this.

Why do you recommend replacement of these two caps?

For what it's worth, I'm getting poor continuity on C907--or at least, it's just for a fraction of a second, and then no more. IC904B has consistent continuity. Is this significant?

https://ibb.co/h2gHZVQ

[SLK001]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

A capacitor does NOT have ANY continuity. What you are seeing is the charging of the cap by your meter, which makes it seem that there is continuity, but it is a false indication. If you DO see constant continuity on a cap, it is most likely blown and shorted, so replace it.

I'm not sure how you are measuring continuity on an IC.

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

That IC901 is the standby ic, It is always on and sometimes those caps can dry up. If you don't have an esr or capacitor checker, (you can't check them with a ohm meter) Just spend the 20 cents and replace them.

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

Right, you are correct SLK--a cap shouldn't have continuity! I wasn't thinking. I don't typically measure caps so I'm not sure how to explain that behavior other than what you suggested.

R_J, mind if I pick your brain to understand this better? What clue'd you into those caps? And what is standby IC?

I'll go ahead and replace them and report back. Thanks for the help.

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

When the tv is turned OFF, the main part of the power supply is off, the only power supply that is on is the standby, which supplies a small voltage to the main board for the micro to operate and watch for a remote command or power button push.
Those two caps are for the ic's VCC and if weak could effect the ic's operation and it operates as long as the tv is plugged in.
Here is a very similar circuit

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

I finally got the IC from China and was able to replace it and the capacitors. Unfortunately, this didn't solve the problem. The TV still displays no picture, and the LED does not light-up.

I measured the voltage from the board's ground to VCC of the IC and got 9VAC. Double checked the fuse (was never in doubt) and I have continuity across it.

Checked from GND of IC to VCC and had fluctuating voltage. This seems like it could be significant, but I'm not positive.

Anything else anyone recommends checking?

Edit:
I took some more measurements across the IC and board, and found that many voltages are fluctuating. Whether I use DC or AC on my DMM, many components appear to not be in any type of steady-state voltage. Maybe this is normal for this board--I'm a bit puzzled.

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

You are using the wrong ground when you are checking the ic. you must use the HOT ground, not the chassis ground.
The ic is only for the standby voltage, do you have the standby voltage now that the ic is replaced?

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

OK, using the hot ground, I am getting 60-61VAC on all IC terminals. Therefore, it appears that I have standby voltage.

Edit: In case it's significant, I measured many of the resistors on the secondary circuit on the power board, and received 66VAC.

[budm]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

OK, using the hot ground, I am getting 60-61VAC on all IC terminals. Therefore, it appears that I have standby voltage.

Edit: In case it's significant, I measured many of the resistors on the secondary circuit on the power board, and received 66VAC.

You use the wrong ground still, Hot Ground in this case means the negative legs of the main filter cap in the hot side.
So are you saying you have standby Voltage on the cold side?'
How about uploading the pictures so we can see what we are dealing with.

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

I understood hot-ground to refer to the "negative" of the 120V from the wall. Here is a picture of my circuit board.

I think what I did actually only indicates that I have no power across the components. The voltage is the same as the line voltage. Where is the main filter cap? Is it the large capacitor in brown at the bottom left of the board?

[budm]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

The main filter cap is the brown cap rated 450VDC.
Negative leg of the filter cap the circuit ground ref point for the hot side circuit ground.
So why are you measuring AC?

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

Measuring the voltage between the negative leg of main filter cap and each pin on the IC, I got the following results (in DC):

Pin1 (top left): 0
Pin2: 0
Pin3: 0
Pin4: 0
Pin5 (VCC): 10-20V (consistently varies wildly, it is unstable)
Pin7: 166V
Pin8: 166V

Measuring D902B bottom-side results in same fluctuating voltage as Pin5, so I assume this is upstream thing? Not sure if this is even something to be concerned about?

(I began measuring VAC when I had difficulty getting stable voltages with my erroneous method)

[budm]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

OK, using the hot ground, I am getting 60-61VAC on all IC terminals. Therefore, it appears that I have standby voltage.

Edit: In case it's significant, I measured many of the resistors on the secondary circuit on the power board, and received 66VAC.

So the question is, are you getting standby Voltage on the cold side or not when you measure the Voltage on the connector that goes to the main board?

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

Check the zener diodes around the ic, the one connected to pin 4 might be bad, or the optocoupler could be damaged

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

Thanks for the replies. I wasn't available during the week so I couldn't reply.

Using an un-powered circuit, I investigated the diodes surrounding the IC and everything had a forward voltage of 0.6V, except for ZD909 (to left of IC). It had 2.1 ohm resistance, and 0V reading (using diode setting on DMM), in either direction. This seems to indicate that it's toast, no?

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

ZD909 has a resistor (4R7Ω) across it, so it is likley ok but to be sure just unsolder one end of the diode and check it

Check the resistance of the transformer feedback winding, betweens pins 1 & 4 of T901,it should be less than 1Ω, then check the resistors, R908a~c they should read about 1Ω total.

[aecune]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

1) I pulled ZD909 out half-way, and I was getting 0.018V in both orientations. This seems to confirm that it's kaput.

2) I checked resistance across what I think is pin 1 and 4 of T901 and got 0.5Ω. Picture is attached of this resistance reading.

3) I'm not sure where R908A-C are. Did you take those values from my screenshot? I was not able to find any resistors of this number, nor any that had an A-C series.

[R_J]

Re: Vizio E550i-B2 no power, no sound, no LED -- blown IC found

I was only going by a sj picture of the board for the resistors, maybe your board is different