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**tom66** · 10-31-2014, 04:46 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Yes, it wouldn't start with a 60W bulb but with a 100W bulb it will bring up VAD and VSCN and sit there with a weak sustain waveform. I'm keeping the 150W for the final power up...

So, I'm going to abort putting the devices on due to finding a fault with IC502. Gate drive to the upper IGBT is missing, it wouldn't surprise me if this is damaged along with that odd Qxxx dual transistor...

This would probably lead the failure of the other transistors, due to lack of ERC...

To do this test I had two probes, one on the emitter and the other on the gate. I also checked the input to the driver IC and this was OK...

- First waveform shows gate&emitter, no difference
- Second waveform shows input to gate IC

Attached Files

**Alastair E** · 10-31-2014, 05:08 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

I dunno why they use that dual-transistor device, Its an NPN/PNP combo emitters/bases strapped, collectors to supply and deck with the inputs on the bases and output on emitters...

I think--total guess-- it must be a way to ensure hard switching of the ERC stage devices,--maybe they have a high gate-capacitance and a straight drive from the chip cant drive 'em fast enough--Dunno.....

You could pull that off the board and re-test waveforms see if the drive is looking reasonable then....
Both the chip and the dual are supplied with DC from a 20? ohm resistor, Thats worth checking, in my set this part had obviously had a hot life.....

**tom66** · 10-31-2014, 05:30 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

SUS_UP driver also appears to have failed in a similar manner, so will also have to replace that.

As for why they use the dual transistor it's probably a cost thing. It also gives approx 2-3x more current gain which will switch the devices faster, reducing power dissipation.

**Alastair E** · 10-31-2014, 05:41 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Have you noticed the Gate-Resistors of the SUS_Up/Dn devices....?

7.5 Ohms, rather than the more usual 5.1 ohm for fast switch/low dissipation.....
--I speculated this may be deliberate for EMC, being its the SUS there's a whole lot of current going on, just great for EMI......

Oh--Forgot to say, The set I did, SUS_Up/Dn I replaced both devices in each--But spaced them over to use the Unused space, ie--separating them on the board, thought this would help thermally--Maybe a bad idea--Like Vestel's Diodes though What you reckon?
--These devices are paralleled, so theoretically Should be matched for V-CE at say, 10A
Bet Pan. didn't and Ive not heard of anyone mentioning anything about it either....

Current-hogging also happens to IGBT's--just like bipolar.....

**tw2005** · 10-31-2014, 05:45 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

out of curiosity what resistance do you have for those transistors at the points marked?

Attached Files

**tom66** · 10-31-2014, 05:51 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

@tw, 0.4 ohms for right (dead short?), 30kohm for left.

A quick test, 15V_F only measures 3.7V? Not sure why, could be cause of missing gate waveforms... could be bad IC502/Qxxx loading it down...

@Al, the change from 5.1R to 7.5R is not necessarily EMC. The resistor is also there to limit gate ringing, which can also increase power dissipation. It is a value that is dependent entirely on the board and the driver design. For example maybe the Toshiba value assumes a 5 ohm gate driver but Panasonic used a 1 ohm one.

There is a lot of thermal theory... dissipation in these devices is primarily in the PCB material so spacing them out ought to help... however I think the best "fix" will be to add some proper heatsinks to the actual devices. I have some ideas...

**tom66** · 10-31-2014, 06:01 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

ah... the 15V_F is boot-strapped... it needs a switching waveform to work... so without one, it will not switch properly, I think. Maybe.

**tw2005** · 10-31-2014, 06:10 PM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Originally posted by tom66 View Post

@tw, 0.4 ohms for right (dead short?), 30kohm for left.

A quick test, 15V_F only measures 3.7V? Not sure why, could be cause of missing gate waveforms... could be bad IC502/Qxxx loading it down...

@Al, the change from 5.1R to 7.5R is not necessarily EMC. The resistor is also there to limit gate ringing, which can also increase power dissipation. It is a value that is dependent entirely on the board and the driver design. For example maybe the Toshiba value assumes a 5 ohm gate driver but Panasonic used a 1 ohm one.

There is a lot of thermal theory... dissipation in these devices is primarily in the PCB material so spacing them out ought to help... however I think the best "fix" will be to add some proper heatsinks to the actual devices. I have some ideas...

Not sure if we're on the same page. measure top pair (opposing sides), and bottom pair. Sounds like you've gone left (top bottom) & Right (top bottom)

my fault

Attached Files

**tom66** · 11-01-2014, 02:27 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Hmm, I'll have a look later then.

**tom66** · 11-01-2014, 04:57 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Top, ~25kohm
Bottom, 10.7 ohm

**tom66** · 11-01-2014, 05:04 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

OK, IC16502 is definitely shorted. 0.0 ohms from Vcc to SW. (That would cook a new IGBT easily!)

The Q16531 is probably OK but I will replace that too (B1HFPFA00001 / CPH5524), the 10 ohms is because of the 10 ohm resistor between output of IC16502 and base of Q16531.

**tom66** · 11-01-2014, 05:24 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

IC16501 & Q16501 test ok, but I will replace them too. They are surprisingly cheap from CHS only about £1.50 each.

**tw2005** · 11-01-2014, 05:36 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Originally posted by tom66 View Post

Top, ~25kohm
Bottom, 10.7 ohm

That's way different to the 5081 boards. 3-3.5meg but if the FET driver is bad they go low like 100-200 ohms.

These have a different FET driver , I think by ROHM.

Do you know the part number of the driver?

I'll check out the schematic and see what you're referring to (in your next post)

I'm just curious to see what can be applied to other boards fault finding wise from the 2010 models.

**tom66** · 11-01-2014, 05:48 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

The fet driver has failed short completely on this, 0.7 ohms to SW to VCC (very bad as it would keep the IGBT on!)

Funny thing I just tried (by accident and then replicated it...), operated the set in its normal mode, waited for LEDs to glow, pulled the series bulb out (disconnecting SN power.) The SN then became powered by the SS board thru the plasma panel, Vsus on SN sagged to 75V... but everything worked (VSCN, VAD ok, ERC ok, LED got a little dim but still going and still no error code...)

It just goes to show how a plasma panel really is just a big capacitor between SN and SS boards!

Only schematic I could find was awfully blurry, attached, maybe you've got a better one?

Attached Files

panasonic_tc-p42s30_chassis_gpf14du.pdf (6.26 MB, 24 views)

**tom66** · 11-01-2014, 05:52 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Driver part number D86903 (Panasonic C0ZBZ0001822)

**tw2005** · 11-01-2014, 06:11 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Originally posted by tom66 View Post

The fet driver has failed short completely on this, 0.7 ohms to SW to VCC (very bad as it would keep the IGBT on!)

Funny thing I just tried (by accident and then replicated it...), operated the set in its normal mode, waited for LEDs to glow, pulled the series bulb out (disconnecting SN power.) The SN then became powered by the SS board thru the plasma panel, Vsus on SN sagged to 75V... but everything worked (VSCN, VAD ok, ERC ok, LED got a little dim but still going and still no error code...)

It just goes to show how a plasma panel really is just a big capacitor between SN and SS boards!

Only schematic I could find was awfully blurry, attached, maybe you've got a better one?

You're one mad professor. No, i got what you and everyone else has, however I have stumbled across Brazilian manuals which have much better detail. Actually, I'll look in there for that driver.. I think it actually starts BD..... but the B is not on the chip

**tom66** · 11-01-2014, 06:15 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Thanks, that will be useful.
I'm not mad, just eccentric. It's nice to learn new things.

**tw2005** · 11-01-2014, 06:29 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

BD8693FVM-HVTR, by ROHM

Attached Files

**tom66** · 11-01-2014, 06:30 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

Nice, thanks. Can you link to the full service manual? (Time to brush up on my Brazillian Portuguese?)

**tw2005** · 11-01-2014, 06:45 AM

Re: Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

http://elektrotanya.com/panasonic_tc-p50gt30a_[sm].pdf/download.html

It was not there originally , but I think I uploaded this when I found it just googling.

That's all I got, similar to that chinese model engineering cct for the 42x10, very handy for confirming some real part numbers

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Panasonic TX-P42U30B locked out LED (no blink code), SN dead short

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