Vizio 500I-B1 no standby power

[TelMinz]

Re: Vizio 500I-B1 no standby power

Resistors usually fail open, yes. If R9301 checks like a short is is ok, Usually when the ic shorts it blows the resistor but sometimes the ic shorts and blows itself open so the resistor does'nt open, R9301 is basically just a fuse in the supply voltage line to the ic.

I just tried to fix my Vizio with this same power supply with a parts kit I got off ShopJimmy. When I plugged it in the IC9301 exploded like the OP's. I don't know what I did wrong. Is it possible the IC I received was bad?

I was careful to make sure I replaced stuff where is should go, took pictures and even drew a diagram to make sure I didn't put something where it shouldn't go. I've checked the R9301 and JR9301, they are both ok. Did the OP get his fixed.

[TelMinz]

Re: Vizio 500I-B1 no standby power

Found some bad 1.2 ohm resistors at r9311 and r9312. Replaced them and the blown ic9301 with new ones I bought on digikey. But now I’m back to where I started, the tv will turn on after being unplugged for a while, and for a day or two it will work, then I shut it off before bed, and in the morning it doesn’t turn on. I’ve looked at every post I could find on this tv, and every part that is said to be wrong was replaced with the shopjimmy repair kit I bought. What else could cause this kind of issue?

[R_J]

Re: Vizio 500I-B1 no standby power

This sounds like a weak electrolytic cap. Replace C9308 and maybe C9305

[thezboe]

Re: Vizio 500I-B1 no standby power

I've replaced IC9302, but nothing has changed. I get about 0.9V across the primary side of that optocoupler, but I assume that's less that the bias on the LED to get anything out the other side.

[thezboe]

Re: Vizio 500I-B1 no standby power

UPDATE: Some solder connections weren't good enough to have continuity. Some of these solder pads are just destroyed from the previous person to try to fix it.

I now have standby!!! The light is on. I hit the power on button and the lights flicker and go off really quick. Any tips for this new development?

I can hear buzzing on the power board coming from either IC9101 or T9301. It is really fast right when I hit the power button and then it slows down after the backlights flash on and off.

[thezboe]

Re: Vizio 500I-B1 no standby power

The 12V and 24V rails are reading 7V and 9V respectively.
When the power button is hit ps_on goes from 0.4V to 3V or so. So this seems like a power supply issue and not a logic board issue.

The way the other threads have gone, this seems like an IC9101 issue?

[R_J]

Re: Vizio 500I-B1 no standby power

Check the voltage across the main filter cap (C9811or C9812) In standby (tv OFF) the voltage should be around 160vdc, when the power button is pushed this voltage should rise to around 380vdc. If it does, the pfc circuit is working, if it does not the pfc circuit is at fault
If ic9101 was bad, I doubt you would get any secondary voltages, you are getting secondary voltages which are about half of what they should be, this is likely due to onl 160v being supplied to the ic and not 380v

[thezboe]

Re: Vizio 500I-B1 no standby power

Voltage on those caps goes from 167V to 392V when turned on. The standby light turns on when I plug it in, but then fades away after about 10 seconds. Not sure if that is nominal.

[nomoresonys]

Re: Vizio 500I-B1 no standby power

You checked all the diodes?

[R_J]

Re: Vizio 500I-B1 no standby power

Voltage on those caps goes from 167V to 392V when turned on. The standby light turns on when I plug it in, but then fades away after about 10 seconds. Not sure if that is nominal.

This means the pfc circuit is working, Check the value of R9140, it should be a low value ( a few ohms), If it checks open IC9101 will likely be bad


The standby light coming on and fading out could be normal.

[thezboe]

Re: Vizio 500I-B1 no standby power

You checked all the diodes?

I have checked all that I could see and they are all good. I may have missed some on the bottom side since they are small.

[thezboe]

Re: Vizio 500I-B1 no standby power

This means the pfc circuit is working, Check the value of R9140, it should be a low value ( a few ohms), If it checks open IC9101 will likely be bad


The standby light coming on and fading out could be normal.

R9140 reads between 0.3 and 0.4 ohms.

[R_J]

Re: Vizio 500I-B1 no standby power

Check if you are getting VCC to ic9101, it should be pin#1 or check on R9112 (2R2) resistor. The vcc voltage will only be there when the board is ON.
I am guessing ic9101 is a LCS703LG

[thezboe]

Re: Vizio 500I-B1 no standby power

When powered on, pin #1 is at 13.75V

[nomoresonys]

Re: Vizio 500I-B1 no standby power

Maybe check D9103 and D9104.

[thezboe]

Re: Vizio 500I-B1 no standby power

EDIT: found them. checking.

My meter reads 0.1 for both diodes going from both anodes to common cathode. Interestingly, it also reads continuity with the leads reversed (although with a greater reading on the meter).

[thezboe]

Re: Vizio 500I-B1 no standby power

I've ordered another IC9101 (LCS703LG). Unfortunately it's terribly hard to read if the PWM coming off of it to the transformers is correct or not.

On another note, can someone tell me the purpose of the dual schottky diodes D9103 and D9104. Both anodes are connected together on the same trace. I even see the same sort of magic laid out in the spec page for IC9101, but it just doesn't make any sense. My guess is to split the current and heat between the two diodes? But they are on the same chip?

[thezboe]

Re: Vizio 500I-B1 no standby power

I've replaced IC9101 and it appears to still exhibit the same behavior.
I'm at a loss now.

[thezboe]

Re: Vizio 500I-B1 no standby power

It works! I had a bad solder joint on the transistor that's part of the feedback loop to IC9101.

[nomoresonys]

Re: Vizio 500I-B1 no standby power

Nice work, thanks for feedback.