Author Topic: Testing Voltage Through PCB Via? (LEDTV repair help wanted.)  (Read 902 times)

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Offline MiserablePixelsTopic starter

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Testing Voltage Through PCB Via? (LEDTV repair help wanted.)
« on: December 11, 2017, 04:49:17 am »
I'm trying to diagnose my LEDTV mainboard and am following the standby voltage (3.3). It is evidently not sending any signal back to my powersupply to enable the rest of the pins because the rest of my 12v rails don't have any power unless I use a jumper across "POWER ON" and "AC OFF DET", at which point the 12v pins all get a solid 12.5v.

Testing continuity, I find the 3.3v arrives at the mainboard and reaches the bottom of the PCB but when I test the via to see voltage, I get nothing(well 0.002). So there is continuity to the bottom but nearly zero voltage. Shouldn't I be able to see 3.3 on the via?

For reference, the TV is not powering on, no standby lights, no clicking, just nothing. The PS has 3.3v standby voltage and my bridge rectifier is reading in spec but I can't figure out the next step without being able to follow the 3.3 rail to see why nothing is coming back from the mainboard. All the caps look fine, the fuse is fine, nothing appears damaged or shows signs of ever getting hot, no smells, nothing obvious. I'm trying learn something here and prevent adding to the floating garbage island. I can't see any reason why this piece of technology should be wasted.

BTW it is a Sony KDL-55W802A. I'd appreciate any input!  :blah:
 

Offline Rasz

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Re: Testing Voltage Through PCB Via? (LEDTV repair help wanted.)
« Reply #1 on: December 11, 2017, 01:00:16 pm »
is it shorted?
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Offline oventech

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Re: Testing Voltage Through PCB Via? (LEDTV repair help wanted.)
« Reply #2 on: December 12, 2017, 03:59:34 am »
Have seen Via's in which the solder connection was bad. Had to reflow in order to get the board to work. Too much flux in via, plus incomplete thru hole plating.
 

Offline MiserablePixelsTopic starter

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Re: Testing Voltage Through PCB Via? (LEDTV repair help wanted.)
« Reply #3 on: December 14, 2017, 06:27:49 am »
I attempted to reflow the mainboard today, 375F @ 10 minutes. No change.

Something I noticed though was when I unplugged the cable running between the power supply and the main board and ran a lead directly between the 3.3v pin socket on the cable to the male pin on the mb socket, I was able to read 3.3 volts on the via! It confuses me because my meter shows continuity through the cable, but the voltage is getting lost somewhere. So, either the male or femal socket/plug may be bad?

I doubt that this is the root of my whole issue, but it may explain why the rest of my power supply isn't getting signaled by the mainboard. I've ordered a replacement cable and I went ahead and ordered a new mainboard. Hoping it solves the issue. It isn't the method I wanted to use to resolve this but I'm not getting very far on my own.
 


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