Polaroid TLAC03212 Lost power in Lightning Storm

[culcuhain]

Good morning!
My friend gave me this Polaroid TLAC03212 32" tv for free since it lost power in a thunderstorm. I know it would not be just a fuse, we can never be that lucky.
Here we go...

Fuse was indeed dead. I ordered about 10 (in case I blow a few testing...) and desoldered and soldering in the new fuse. Plugged in the Power board and no 5v stby. The fuse did not blow. Checking the bridge rectifier I have 120V on the AC inputs and ~164 on the DC outputs. The Large cap (450v ?82uf) has ~160v DC.
Not sure where to go from here and I cannot find the service manual for this freebie. I am getting better and I appreciate everyone's help!

[CapLeaker]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

You would have to fix that 5V STBY voltage first, if the PSU doesn't have any STBY voltage.

[dick_barton]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

If the fuse was blown but a replacement did not blow, then it is likely that you now have an open circuit device or failed IC. I would test all the diodes and zener diodes to start with.

[culcuhain]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

I have attached a pic of the board and the diodes I tested with my DMM.
When set on diode (tested on board, did not left a leg) all diodes had voltages <1v when the probes were attached, both Black on Diode line side and reversed, with the exception of one. This one showed OL when the red probe on the Line (reversed, I know) so I pulled it and tested it again. Same result, diode should be good.

I did not check any of the SMD diodes on the backside. So I check those next?
Is there a certain trace to follow and test until we find out why there is no 5v standby (I am not worrying about the other voltages at this time.

Many thanks!!

[culcuhain]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

Looks like I found the culprit. Mosfet at Q23. Tester showing it as 2 resistors and not a Mosfet. Part # JCS2N65F. Mouser and Digikey has one close but the RDs Drain Ohms is lower from them. Will that be a problem? I appreciate everyone's help!

[CapLeaker]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

Looks like I found the culprit. Mosfet at Q23. Tester showing it as 2 resistors and not a Mosfet. Part # JCS2N65F. Mouser and Digikey has one close but the RDs Drain Ohms is lower from them. Will that be a problem? I appreciate everyone's help!

That mosfet should be shorted if it is bad. Now you have to check the gate drive circuit of the mosfet. Make sure the resistors are still within its specifications, diodes aren't shorted, etc. If you have to order that mosfet, make sure you don't have to order that PWM IC later. Not that the PWM is automatically have to be bad, but its a bummer if it doesn't work and you have to do another order because of a 1$ part that cost 8 to 25 to ship.

[culcuhain]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

Thank you for the tip about the PWM IC. I will get one ordered. Yeah. Ordering a $1.37 part and paying $8.00 for shipping doesn't make sense. I have a few more friends dropping off tvs for me to fix. so I will just do one order if possible.

[CapLeaker]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

make sure that all components on the path between the PWM and the gate of the Mosfet are good.

[culcuhain]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

MOSFET and IC (forget which one, been awhile) replaced and tv lives.

[CapLeaker]

Re: Polaroid TLAC03212 Lost power in Lightning Storm

Perfect!