Vizio 500I-B1 no standby power

[nomoresonys]

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.

Need to look VERY close at those solder joints whenever you get fluctuating voltages or voltage drops to 0 like that, many times it's a bad joint.

[thezboe]

Re: Vizio 500I-B1 no standby power

I ran across a video on Youtube that gave a great description of all the parts of a switching mode power supply. The key was that if you're voltages off the dual diodes are low, that usually means that something is happening with the feedback circuit that goes through the optocoupler back to the primary side. I figured it was the opto itself, but it tested good so I started tracing it all the way back to the transformer. Honestly, I should've checked that solder job sooner since the previous person that tried to fix it really messed up everything else, and that's one of the things they tried to fix.

Oh well, here's to learning.

[nomoresonys]

Re: Vizio 500I-B1 no standby power

You gave a good clue in post #12 you said the previous guy botched up the soldering which should have led me to suggest checking the joints closely, don't know how I missed it.

[thezboe]

Re: Vizio 500I-B1 no standby power

Well the TV worked for one night and now it's kaput again.

I have standby voltage, and I can turn it on and the light goes solid but no backlights. I am getting like 1.8 volts to both the 12v and 24V(18V?) pins. The transistor labeled IC9103 was the pain point that I fixed that made it started working last time. The solder job is still good so it must be something else.

Let's try this again, shall we?
What do the R/A/K letters mean on the labeling for the terminals of IC9301?

[thezboe]

Re: Vizio 500I-B1 no standby power

So I'm looking into this set again after a while of just letting it sit. I opened it up and just figured I'd power it up just to see and it powered on fine! Left it going for the night and turned it off a while ago. Tried to turn it back on and it's displaying the same issue. Backlights flicker on real quick and then back off. The sound works fine however. Any ideas what it could be?

[nomoresonys]

Re: Vizio 500I-B1 no standby power

Maybe test the powerboard, with cable from powrboard to mainboard UNPLUGGED, use 3 resistors in the 1k range, jump one from PS_ON to +5V, another from on/off to +5v and the other from dim to +5v, plug power into powerboard, see if you get the proper voltages and if backlights come on and stay on.

[thezboe]

Re: Vizio 500I-B1 no standby power

I will try that tonight.

I also was looking at the output voltages when this is happening. The 5V and 12V rails are good, but the 24V rail is reading something like 15.6V. It seems pretty rock solid at that voltage, so it doesn't seem like a feedback loop issue to me. Maybe a bad cap on the cold side?

[thezboe]

Re: Vizio 500I-B1 no standby power

That didn't do anything for me. No reaction at all from the power board, only the 5V standby was on. No 12V or reading on the 24V line. so it seems to not be signalling to the power supply to "turn on".

When the board powers up with the cable plugged in, the voltage to PS_ON, ON_OFF both read 3.3V thereabouts. But the DIM pin reads like 0.05V.

[R_J]

Re: Vizio 500I-B1 no standby power

If you are getting +12 volts, and no +24 volts, Check all the connections from D9106 & D9103 to the plug. +12v & +24v come from the same transformer.

[thezboe]

Re: Vizio 500I-B1 no standby power

Does IC9101 provide the 24V or the 12V rail? I see the sort of "voltage divider" with the transformers. The 12V rail is coming out okay, but the 24V rail is not correct.

Every now and then I can get the TV to power on and work perfectly. When it happened the last time, the 24V rail was reading 15V! So I'm not sure what the difference is when the TV powers up and when it doesn't currently since the power rails seem to be the same in either case.

[budwich]

Re: Vizio 500I-B1 no standby power

seems potentially like the other recent thread which now points at a led issue.

try unplugging one of the cables going to the backlights from the inverter. What happens in the start up? Do the same test again, trying the other cable.

[R_J]

Re: Vizio 500I-B1 no standby power

I will try that tonight.

I also was looking at the output voltages when this is happening. The 5V and 12V rails are good, but the 24V rail is reading something like 15.6V. It seems pretty rock solid at that voltage, so it doesn't seem like a feedback loop issue to me. Maybe a bad cap on the cold side?

I checked a few other threads and I believe the 24v marked on the board is usually around 16~19VDC.
https://www.badcaps.net/forum/showthread.php?t=59528