Vizio VF550M Main Board Problems

[ttuguy]

I found a Vizio VF550M 55" 120Hz LED TV on the curb set out for trash pickup, I grabbed it hoping it was just bad capacitors as I've done this repair on many items over the years. However quick inspection showed that none of the capacitors looked puffy. We also just had some bad lightning storms, so I'm starting to think it might have been a surge.

I am 90% sure the main board is toast, but would love the opinion of a more experienced TV repairman. I'd also like to know if you think it's worth gambling on a replacement main board or if this thing is likely to be a moneypit (more bad components to come)

The amber standby light comes on, but pushing the power button doesn't fire the relay.

Main filter cap is ~168V (as expected for 115V mains).

I disconnected all boards and jumpered STBY to the PSOn and the relay fired.

Measured 5V, 12V, 18V and 24V rails all good (w/ multimeter don't currently have scope access).

Plugged everything back in and noticed one of the two HDMI switch ICs is getting very hot even with the system on standby (probably gets standby power to turn on when a connected device is turned on). The LDO feeding it was also getting warm. I inspected the immediate area for FOD but found none, so I desoldered the HDMI switch (I have the skill to replace if needed) hoping that it was just pulling the rail down (didn't check first because I am a dumb-A).

The LDO is operating correctly and nothing is heating up, but the power button still does not cause any voltage to be applied to PsOn. I wouldn't expect the missing HDMI switch to matter, so I'm guessing something else is bad.

Anything else I should try before ordering a replacement main board?

Is it even worth trying to replace the main board (found one for $120, 15% restocking free + return shipping)? I'm scared I'm going to get the main board replaced and find out the all 3 of the other boards are toast, is this common?

Thanks for your comments!

[maxvalutech]

Re: Vizio VF550M Main Board Problems

I'm only a potterer but did you main caps voltage increase too when PSB jumpered and did backlight come on. If so then I would think main with problem not sending ps-on voltage back and the tcon would be a ? mark for later - but does it get its 12v now?

[ttuguy]

Re: Vizio VF550M Main Board Problems

Thanks for the suggestions.

OK if the main board is connected and Tcon disconnected the backlights don't come on, all of the supplies (5,12,18,24) are at rated voltage and every cap I could get to on the main board has either 5V or 3.3V on it and nothing is really getting hot (second HDMI switch is probably warmer than it should be with no signals).

If I disconnect the main board both backlights come on, intensity looks good, no obvious cracks in the LCD panel.

[ozzy214]

Re: Vizio VF550M Main Board Problems

I would say main is toasted. Most likely surge came through hdmi or coax spiking main. I would start with a known good main and worse case in the end the t con. But I highly think the t con dead.

[ttuguy]

Re: Vizio VF550M Main Board Problems

worse case in the end the t con. But I highly think the t con dead.

I'm hoping you mean highly doubt the t con is dead?

[CapLeaker]

Re: Vizio VF550M Main Board Problems

Check the lvds signal with an oscilloscope. That will tell you if the main or the Tcon is bad.