Repairing a power board for a Vizio P75-C1

[Brogan]

Our TV popped the other night.

I have identified the component involved - R9101 on the large power board.

Granted there may be other problems which caused it to blow, but I'm going to try just replacing this first to see if it resolves it.

The board part number is ADTVF1035AA6.

The resistor looks like it's red, yellow, grey, gold, green.
Which makes it a 24.8 ohm, 0.5%.
Based on the width, about 4mm diameter, and 10mm long, I'm guessing about 1/2 to 1W?

The biggest problem is trying to source a replacement.

I'm not averse to putting a couple in series to get the correct resistance, but I'd rather get an exact match.

Can anyone help?

 

[Tha fios agaibh]

Unsolder one lead and measure its resistance.
I'll bet there's nothing wrong with it.

Looks like high voltage jumped across the jumpers beneath it and fried the paint off it a wee bit.

I'd start by looking for shorted diodes, transistors or whatever components are in the path of those jumpers.

 

[Brogan]

Thanks, I already did that yesterday.

It is most definitely an ex-resistor.

I can't see any other damage on the rest of the board and components - I checked with a magnifying glass to get a good look.

 

[Tha fios agaibh]

Digikey has 24.9Ω 0.6W in stock.
Probably close enough.

https://www.digikey.com/en/products...mfrgC0caFJQYOPhEIBI0fAIgvsQASpgG7AbIeKgaxnxAA

 

[Brogan]

Thank you!

I scoured that site yesterday but didn't find that.

 

[Brogan]

Digikey has 24.9Ω 0.6W in stock.
Probably close enough.

https://www.digikey.com/en/products...mfrgC0caFJQYOPhEIBI0fAIgvsQASpgG7AbIeKgaxnxAA

I was going to order that and then I thought 0.6W is probably not a high enough rating.

That one is 2.5mm dia and 6.5mm long.
The one I need to replace is 4mm dia and 10mm long.

It's so frustrating that Vizio won't give me the spec's of the component.
They clearly know it - they must have the circuit diagram and component list.

 

[Tha fios agaibh]

24.8Ω, 3/4W
https://www.digikey.com/en/products/detail/vishay-dale/RNC70H2482DMB14/10520024

 

[PETERDECO]

Put two 47 to 50 ohm 1W resistors in parallel.

 

[Brogan]

24.8Ω, 3/4W
https://www.digikey.com/en/products/detail/vishay-dale/RNC70H2482DMB14/10520024

Unfortunately same problem as most of the stock.

 

[Brogan]

Put two 47 to 50 ohm 1W resistors in parallel.

I am considering MacGyvering something.

However, I would likely go with a series set up.

I wouldn't want one of the resistors to fail and act as a shunt.

 

[PETERDECO]

If you're concerned about power dissipation, the 2 in parallel will double it.

 

[Tha fios agaibh]

I wouldn't want one of the resistors to fail and act as a shunt.

It appears to me that the resistor failed from voltage arcing from jumper wire to bottom of resistor with poor insulation.
I would either try moving jumpers to other side of board and insulate them with shrink tube, or just add shrink tube or other means of insulation.
Then if you can source a replacement, go with PeterDecos idea of using two resistors. Perhaps a 47Ω and 51Ω to get it a little closer to the 24.8Ω you want?

 

[Brogan]

The TV's been running for 5 years so I don't feel the need to redesign the board.

I'll just see what I can cobble together so I can power it on to determine if there's a bigger problem.

 

[Tha fios agaibh]

The TV's been running for 5 years so I don't feel the need to redesign the board.

I wouldn't call it redesigning, rather just mitigating the chances of it shorting out again.

 

[Brogan]

I've found some 1 watt resistors on ebay.

The current resistor is 24.8 +/- 0.5% which gives a range of 24.676 - 24.92.

The two resistors I've found are 24 and 0.82 +/- 1%.
That gives them ranges of 23.76 - 24.24 and 0.8118 - 0.8282 respectively.
Combined the range would be 24.5718 - 25.0682.

That is within acceptable tolerances I think - it's 0.1042 on the low end and 0.1482 at the high end.

This is with the two resistors in series.

I know some have suggested parallel but I don't like that idea due to the shunt possibility and also because they will draw too much current.

 

[Brogan]

Update!

I decided to to another more thorough check, tracing the path back, and found a burnt capacitor, which likely triggered the resistor blowing.



So now I need 2 components I don't know the exact values of ...

 

[Martaine2005]

I checked with a magnifying glass to get a good look.

I don’t think your magnifying glass works very well!

 

[Brogan]

More so my eyes.

The capacitor was bent over and showed no signs of damage on the other side, which is why I missed it the first time.

 

[Martaine2005]

Have a look at the other capacitors near other heat sinks. They are probably very similar or the same.

Martin

 

[Brogan]

I did another check after I found this one - these two components appear to be the only damaged ones.

I have no way of knowing what value this capacitor is - the markings were on the side which is burnt, so it looks like my only option now is to get a replacement board.

Vizio have been singularly useless in providing the schematics or component specs.