Panasonic th-42phd6 dead but has green led

[freakaftr8]

so I'm repairing this TV for a friend. TV powers up with green light and immediately you hear a high pitch whine from the power supply board then a second later click the TV shuts down but the green LED stays lit. Fans shut down with the click and I'm getting high voltage to the SC and SS boards. I've tried disconnecting each board and I still get the high pitch whine and the green light stays lit but everything powers down. Having my assumptions that the power supply board is indeed faulty but not too sure yet I've tried disconnecting buffer boards and that didn't help. I checked for shorted MOSFETs and I can't find any. What's odd is that on the SS board the red LED attempts to light up but not on the SC. Any ideas?

[tom66]

Re: Panasonic th-42phd6 dead but has green led

Do you have Vsus, Vda and 15V?
On SC board, is -Vad and Vscn present?

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

Hi Tom. That's what I'm curious about. Most Panasonic plasmas that I work on have clear labels on the boards for test points this one doesn't have any I don't know where all the voltages derived from the power supply is no label on the screen depicting I can't find a service manual.
VSUS voltage is fine that comes up and then powers down immediately

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

for the moment that I can get it to power up it appears that I have all voltages. Vda reads 35v. VSUS 173v. 15v comes up but won't stay on long enough to to read properly. On sc vscan and vad present. Vscan does not have enough time to come up I can only read about 14 volts vad -60v.

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

I guess I should say that originally I said a high pitch whine from the power supply it's not really a whine it almost sounds like a beep from a digital watch. and it's either coming from one is large filter caps or a transformer

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

Power supply model tnpa2889 and the sounds coming from the hot side.its hard to isolate

[Caleb]

Re: Panasonic th-42phd6 dead but has green led

I've had several chirping power supplies ( not panasonics though) that had shorted output diodes. I would say it is in the secondary or possibly heavy load from another board otherwise it would blow the fuse.

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

True. But thus a dead beep like sound for only a split second then all voltages shutdown after the relay clicks out. I've attempted to isolate sc board but the way panasonic are wired it's impossible to isolate SS board.

[tom66]

Re: Panasonic th-42phd6 dead but has green led

FWIW, I've had some whining power supplies where the whine is normal. Including an older Panasonic (PV500, similar generation to PHD6.)

[Caleb]

Re: Panasonic th-42phd6 dead but has green led

Have you resistance tested the secondaries?

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

yes I have resistance tested the secondaries already. this is not like the other chrips are flubs I have heard on power supplies relating to loose coils or chokes this is definitely a sound of a that short of some type but oddly I can't seem to find any shorted components on the power supply board thus far

[Caleb]

Re: Panasonic th-42phd6 dead but has green led

Only way I can think of to isolate is by pulling individual outputs out of the connector until you find the overloaded one, that is assuming that its not on the power supply. Could be that the short is beyond a relay in which case you would have to current test each voltage source. Maybe Tom has a cheat sheet showing how to fire the power supply without any boards connected?

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

hopefully because I have tested both sustain boards and are goodI've also checked almost every diode resistor in my set transistor on the power supply and all tests within spec but I'm getting this odd sound out of the hot side of the power supply near where the mains connect and the power supply only spins up for a split second then clicks with a shutdown but the green light is still on. I've never seen a Panasonic Plasma shutdown without an error code.
also in my experience if there's a dead short on the hot side of the power supply it would blow something up in the TV wouldn't work at all because that side of the power supply is always on. This sound may be coming from a transformer that's rather small but it's really hard to tell by ear.
btw power supply model is tnpa2889.

[tw2005]

Re: Panasonic th-42phd6 dead but has green led

hopefully because I have tested both sustain boards and are goodI've also checked almost every diode resistor in my set transistor on the power supply and all tests within spec but I'm getting this odd sound out of the hot side of the power supply near where the mains connect and the power supply only spins up for a split second then clicks with a shutdown but the green light is still on. I've never seen a Panasonic Plasma shutdown without an error code.
also in my experience if there's a dead short on the hot side of the power supply it would blow something up in the TV wouldn't work at all because that side of the power supply is always on. This sound may be coming from a transformer that's rather small but it's really hard to tell by ear.
btw power supply model is tnpa2889.

It's a pretty old model so would not expect the same level of onboard monitoring. i know i briefly touched a 2005 panny and it had a main board issue and shutdown, no error blinks on that one either. Just sat there with a non responsive red LED , how rude.

I have a huge 4 part PPT presentation for the 2006 PD60 maybe there's something that can be used for fault finding? Not sure if I can upload would take a long time

[tw2005]

Re: Panasonic th-42phd6 dead but has green led

42PX25 has same PSU

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

Nice thanks a million! Going to look into these schematics.

[freakaftr8]

Re: Panasonic th-42phd6 dead but has green led

Well all voltages appear to be there. The 7 v standby is low at 5v. The 5v is spot on but 12 and 15 appear to be low. But hard to tell at split second intervals. I might be looking for a capacitor issue possibly. Have to r an esr over them. None appear shorted although.