Vizio SV420XVT1A no picture has sound

[electronics_repair111]

Hello,

I need help with troubleshooting a Vizio tv. Tv had a bad t-con board (processor and memory was burnt. Replaced t-con, when tv powered up the t-con's LED lit up blue then faded out while a screeching sound was emitted from the t-con. I didn't see a picture even when volume or menu button was pressed (back-light is on but no image at all). I disconnected the LCD panel (two ribbon cables) powered it on and it didn't make the screech sound. Is the LCD panel bad and overloading the t-con? Is there anyway to test the LCD panel? Any tips would be greatly appreciated.

 

[BeerBelly]

Most of these failures are due to electrolytic caps. Look around the PC boards and see if one is bulging or leaking. If you spot one then replace all of the caps which look identical to the bad one(same voltage, value, temperature rating, manufacture).

 

[Nigel Goodwin]

I would imagine you've probably killed the new T-con board, possibly the HT rails are too high and destroying them?.

 

[electronics_repair111]

Thank you BeerBelly, I have already checked for defective caps but I will check again. much appriciated

 

[electronics_repair111]

I would imagine you've probably killed the new T-con board, possibly the HT rails are too high and destroying them?.

Thank you Nigel, I hope have not damaged it but what does (HT Rails) mean and how do I test that? Thanks again

 

[rmn_tech]

HT = High tension (high Voltage) e.g. Vs=203v, Va=173v

 

[electronics_repair111]

HT = High tension (high Voltage) e.g. Vs=203v, Va=173v

Thank you RMN_TECH, I understand now lol. I was thinking it was referencing the lcd panel or t-con connections. The TV was in a cabin so a surge was a possibility.

 

[Nigel Goodwin]

HT = High tension (high Voltage) e.g. Vs=203v, Va=173v

Not specifically - HT rails refers to the power rails in a unit, so 12V and 5V are 'HT' as well.

Historically it refers to 'High Tension', which was high voltage rails in valve amps etc.

LCD's don't have high voltage rails though, only high voltages in the inverter feeding the CCFL's.

 

[Nigel Goodwin]

Thank you BeerBelly, I have already checked for defective caps but I will check again. much appriciated

How did you check?, either an ESR meter or a scope are the only ways.

 

[rmn_tech]

I stand corrected Nigel I somehow started thinking Plasma. The plot has finally been lost

Anti ageing machine anyone.

 

[electronics_repair111]

How did you check?, either an ESR meter or a scope are the only ways.

I did a visual (looking for pregnant ones) but I will break out the trusty ESR meter I could also look at the out puts of PS with a scope as well. I did notice the 12VDC was under, it was around 11.85VDC. Just curious what is a way to gage the min and max of given voltages? like a 5% rule or something? Thank you again for all the input

 

[BeerBelly]

I expect anything above 11.65 is probably OK provided you don't have too much ripple.

 

[electronics_repair111]

I expect anything above 11.65 is probably OK provided you don't have too much ripple.

Thank you BeerBelly Exactly what would be considered to much ripple, like 500 mv or would it be a percent of the voltage?

 

[BeerBelly]

It depends on the circuit, but if I had 200mv ripple I would try bridging a capacitor across the supply line to see if that cures the symptom.