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

[aecune]

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

OK I see it now. I was looking for the element from the top-side of the board. Values are:
R908A - 1.5Ω
R908B - 1.5Ω
R908C - 1.5Ω

[R_J]

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

Ok, those are ok, It is likely just the shorted ZD909 that is causing the ic not to operate. with the current sense resistors shorted by the zener the ic will likely shut down for protection after a couple cycles.

[aecune]

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

Thanks a lot for the help so far, R_J and budm. I have one question regarding identifying ZD909; it is marked NZ 4V7D or NZ 4V70--it's hard to distinguish the last letter. Regardless, I cannot find anything online with this information, except, incidentally, another badcaps thread thread with you gentleman in it :-)

https://www.badcaps.net/forum/showthread.php?p=851050

Within that thread, budm had the following exchange:
OP: "Only found 2 bad diodes. zd909 which is a nz4v7d replaced with a nz6v8b"
budm: "I would out in the same value, they put 4.7V Zener for reason"

If this is a 4.7V diode, what other specs should I look for in a replacement diode, for example, current, impedance, etc?

[R_J]

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

A 4.7v 1 watt zener would be fine. it's not that critical. Its just to protect the ic's source input from any voltage spikes that might occur. The source pin maximum is around 7v

[aecune]

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

I replaced the zener, but still no dice. Going to recheck all my soldering tomorrow as best as I can, though I'm not 100% sure of which items connect to which, without a wiring diagram for this board. I'll also check voltages on various nodes to see if there are changes in the voltage.

[aecune]

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

Did more testing of the voltages, as well as checking the resistors again. Also checked continuity.

1) Found nothing continuous with Pin1 + 3 of IC901. 3 is GND--maybe no issue. 1 is "S", which is source terminal of internal power MOSFET. PDF recommends connecting with a sense resistor to GND--maybe also not an issue.
edit: Pin 1 and 3 are continuous with an elements closer to the main cap, so soldering is not an issue.

2) Many of the resistors appear to have no power across them, as their voltages appear identical on both sides.

3) R804A, which is near the main cap, has 0.2 ohms of resistance. It's marking is 0.068Ω (68mΩ). Maybe a problem. Shown in second uploaded picture.

4) ZD909 (which has been replaced) is showing no forward voltage again, while connected to the circuit (I know this isn't best way, but it's showing same characteristic as previously replaced diode, unlike the other zeners)

edit: all voltages are taken with regards to the negative leg of the main cap.
Also, where and what voltage tells us the cold side is getting powered successfully, and therefore IC901 is repaired?

[R_J]

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

R804 is likely good, you need to consider your meter lead resistance whne checking very low value resistors. What is the resistance with your meter probes shorted together

[aecune]

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

R804 is likely good, you need to consider your meter lead resistance whne checking very low value resistors. What is the resistance with your meter probes shorted together

Good question. It's 0.1 ohm. So the measured value of R804 is within a rounding error.

Any other ideas? Did you see anything strange with my voltage readings in the picture of my last post?

[aecune]

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

I replaced the power board and now my TV is back online. Thanks for the effort, all.

I'm going to try to find the root cause by comparing the two. I would still love any assistance if anyone is interested in getting to the root cause here, as the original board is still broken.

Edit: Found that C910 and C908 have different values while in circuit, which seems to indicate something nearby is different. This is shown in picture. Capacitors in red have 73uF capacitance in good board, 140uF in bad board.

I started looking around the IC when I found that the new PCB has very stable voltage (~18V) on Pin 5 of IC901--while connected--whereas the old board did not (fluctuated 12-24V).

I measured many of the diodes and resistors around IC901 and found them to be identical.

[R_J]

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

Regarding C908, Have a look at the other side of the board. C910 is a disc cap, likel a few pico farad. Are you checking and comparing both boards voltages in standby?

[aecune]

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

Regarding C908, Have a look at the other side of the board. C910 is a disc cap, likel a few pico farad. Are you checking and comparing both boards voltages in standby?

Yes, both boards were in standby (power connected, but not turned on).

A little bit amusing maybe.. there is no element on the topside at C910. So.. I'm not sure what to think about that.

[Digital_Dad]

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

Yes, both boards were in standby (power connected, but not turned on).

A little bit amusing maybe.. there is no element on the topside at C910. So.. I'm not sure what to think about that.

Have you figured this out?

[dragonwyatt]

Greetings all, reviving this thread. I have this same problem. I've attached an image of my failure... We were watching TV and there was a loud POP, the TV died, and then there was the enjoyable smell.

I found a repair kit of sorts from shopjimmy . com, but they appear to be out of stock.

If the picture there is to be believed, there's IC901, a zener, another diode, and a resistor, but no detail on that page about where the diodes and resistor go...

https://www.shopjimmy.com/component-...ower-supplies/

Any help would be appreciated, I'd love to repair this and keep it out of the landfill!

Thanks in advance!