Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

[mattpd]

I have a hitachi plasma 55HDT79 that at one point had faults in the display. Yesterday when I turned the TV on after replacing a buffer IC (which did solve one of my display faults so I think I got it right) it ran for a minute then I heard a POP and the display went out completely, but the TV continued to run with sound.

When the tv is running and I test VS on the power board I get 0v. The 5v and 11v supply's test OK. My question is can I assume the power board is malifunctioning, or could it be some kind of problem with another board, and the VS is not switching on? Every other psu I have come across puts out VS no matter what...

[drpj23]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

Aren't there fuses on the power supply within the board? (Not sure what line they are connected to though) But check those

[mattpd]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

The only two fuses I can find test good. It's also missing VA and a few other voltages. I'm thinking if the tv turns on and plays sound, these voltages should be present. I'm just worried the tv can sense the y or z board being bad, and that's why there is no voltage.

[tw2005]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

on the plasmas I've worked on if theres a fault on the sustains then it's detected and power is shutdown to them. have not worked on any hitachi but samsung,lg &panasonic

[drpj23]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

What happens when the power supply is isolated? (Nothing connected but main)

[mattpd]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

With just main and logic board powered up, the TV still comes on with sound, but there is still no VS or VA voltage.

[IamCanadian]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

when turning the tv on and with your dmm on the Vsus do you get anything?

[mattpd]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

Call it Vs or Vsus, I don't get a reading. My only concern is that the PSU is "intelligent" enough to not turn on Vs voltage because it senses the ysus is either unhooked/broken. Does it take a ysus and xsus board that are both conected and functional for the PSU to produce Vsus voltage OR does the PSU produce Vsus all the time (when tv is on) when it is functioning correctly?

[drpj23]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

I've always had them constantly on. I am supposed to get a hitachi plasma in the distant future but otherwise, I can't help you much right now.

[IamCanadian]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

Any Time Vs/Va voltages do not appear and a test is made, each time a new test is to be made, Press the Power Button and Turn the Plasma OFF. Wait until you hear a "Click". Unplug the CN68 connector. Re-Plug the CN68 connector. If this is not done, the Turn On command for Vs/Va (Vsago or Vcego) and the 5V of the CN68 connector will not happen.

[mattpd]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

Any Time Vs/Va voltages do not appear and a test is made, each time a new test is to be made, Press the Power Button and Turn the Plasma OFF. Wait until you hear a "Click". Unplug the CN68 connector. Re-Plug the CN68 connector. If this is not done, the Turn On command for Vs/Va (Vsago or Vcego) and the 5V of the CN68 connector will not happen.

Wow, thanks. This is the kind of info I have been looking for, I will do some more tests tomorrow morning. What document is this page from? It's a big help!

[IamCanadian]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

the great GOOGLE has lead me to the Doc, All hail the GOOGLE!

[mattpd]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

While the TV is on I only get 3.3v standby and 3.3v on the N/C. Everything else is missing or or below 0.15v. Bad PSU?

[IamCanadian]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

check fuses on psu, Sounds like that will be a good stating point.

Check the mosfets too

[tom66]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

Pretty sure PSU is bad. I have encountered several plasma PSUs which use a separate fuse (sometimes a tiny thing) for the main supplies and/or Vs/Va supply, so check as the Canadian suggests . Also, make sure you check PS-ON or whatever it is called (refer to service manual.)

[mattpd]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

I will go hunt for the tiny fuses, all the big ones are ok. Would you expect them to be surface mounted? And with the mosfets, should I just test for shorts between pins or do I need to remove them and check their functionality?

[tom66]

Re: Is there any legitimate reason a plasma PSU would not put out Vsus voltage?

Normally everything except control logic on a PSU is through hole. So fuses should be visible. If the fuses are blown, then the MOSFETs are likely short.