Panasonic TH-P42X30A no standby 5 volt

[dkneyle]

[Posting this fault find to help others who might follow later.]

Got this plasma from the dump/tip. Great looking TV with high quality features. Completely dead. No standby supply. Have traced the hot side standby supply through and appears to be OK but have not confirmed that it is actually oscillating. Looking on the cold side I see a SMT diode that appears to rectify the output of the standby transformer. It measures short circuit in circuit. I am about to remove it from the circuit and test out of circuit. Having difficulty reading the type number. I thought I saw LT1402 but nothing appropriate comes up on a Google search.

[ReeceyBurger123]

Re: Panasonic TH-P42X30A no standby 5 volt

Normally that diode is in place to protect the transformer so it probably will show S/C in circuit but fine out of circuit. Can you provide us with some pictures please ?

[dkneyle]

Re: Panasonic TH-P42X30A no standby 5 volt

The suspect diode is D308. You can pretty well follow the circuit by looking at the PCB tracks. The diode sits on the output of the standby transformer and half-wave rectifies the high frequency AC. The filter cap C325 does its job at the output of the diode in question. It does not appear to be a snubber diode.

[ReeceyBurger123]

Re: Panasonic TH-P42X30A no standby 5 volt

You are right now that im looking at it, test it out of circuit and see buddy,

[dkneyle]

Re: Panasonic TH-P42X30A no standby 5 volt

Just pulled it and it is short circuit. Have gone through my junk pile and found a diode from another SMPS that appears to do the same job in circuit. It's a SB2H00. I'll just check its specs then drop it in and see what happens.

[dkneyle]

Re: Panasonic TH-P42X30A no standby 5 volt

All fully operational again. I thought perhaps a short circuit diode would indicate other overload problems and failed components, however all worked fine with a substitute fast switching rectifying diode.

Another fantastic TV saved from landfill!

[tom66]

Re: Panasonic TH-P42X30A no standby 5 volt

Nice. These are good sets, shame they don't use good caps on the PSU though.