Panasonic TH-42PX75U

[Vizor]

Fuse Blowing soon as power is turned on.


i see 2 areas where it looks like it may have gotten hot or maybe i am just dumb . Don't even know where to begin with Panasonic.

[selldoor]

Re: Panasonic TH-42PX75U

In Pic one there is what looks like a bridge rectifier bolted to the heatsink.
This is often the cause of immediate fuse blow. Have you tested it.

Perhaps you could have marked the pics with the heated area and told us which it is on. - save us looking through 14 pics

[tw2005]

Re: Panasonic TH-42PX75U

Fuse Blowing soon as power is turned on.


i see 2 areas where it looks like it may have gotten hot or maybe i am just dumb . Don't even know where to begin with Panasonic.

I've fix the same PSU here in Australia, 42PX7 model. From what I've read they have a common fault, maybe yours is the same.

Check R411, ERF5TJ100, 5W 10ohm - could be open as it's part of the protection

Check Q406 B1DEKQ000003 , this is what failed on mine and blew the fuses + resistor and possibly bridge rectifier (can't remember now)

Check D401 B0FBBT000008, bridge rectifier for short.

Maybe check D417,419,420 B0EAMR000009 they look heat affected but were ok on mine.

Fuses F401,F402 K5D802BNA005, 8A blown- obviously need replacement.

There is a service bulletin mod as well adding a polyester capacitor.

[tw2005]

Re: Panasonic TH-42PX75U

Marked photo.

Oh, don't loose or damage that silicon pad under Q406 if it's replaced. We lost it and did not quite insulate Q406. Sparks, smoke and damaged tracks

[Vizor]

Re: Panasonic TH-42PX75U

In Pic one there is what looks like a bridge rectifier bolted to the heatsink.
This is often the cause of immediate fuse blow. Have you tested it.

Perhaps you could have marked the pics with the heated area and told us which it is on. - save us looking through 14 pics

13 and 14 but mostly 14 and forgot to mention 401 is the only fuse blowing.

[selldoor]

Re: Panasonic TH-42PX75U

Id start with the bridge rectifier test on D401.

[Mark L]

Re: Panasonic TH-42PX75U

Hello everyone,

I'm new here and ran across this thread through a Google search.

I too have a Panasonic TH-42PX75U plasma that has the same symptoms as the OP, no red LED at all. This happened last Christmas 2011 and I ordered a fix-it kit through eBay, (here) I got the TV to work and it ran for a week. I then started a remodel and the TV has been sitting for the last 6 months. I went to hook it back up last week, it turned on fine, ran for about 15 minutes, then went black. I knew I was back and square one and sure enough, both the F401 and F402 fuses were blown.




So here I am back to where I started 7 months ago. I've done a TON of research and reading into this problem and this thread has by far been the most helpful so far. Especially those pdf's uploaded by 'tw2005', thanks for those.




So long story short, I'm contemplating buying a whole new power board, but am hesitant as I don't know this is my only problem. I can get the board for around $100, but I just want to make sure this is all I'll need.




I have ran a series of tests, including testing the D401 bridge rectifier, which to my knowledge (based off this tutorial) is shorted, as I'm getting readings both directions.




I'm trying to figure out how to test my Q406 MOSFET right now, I've been searching for videos on how to properly test it, since it's still in the board right now. Any help with this would be greatly appreciated. I'm assuming I test this via the diode mode on my digital multimeter?




As far as the R411 goes, I have no idea how to test this component, I tried via diode mode, audible diode mode gave me no beep, I get no reading whatsoever when I touch both contact points. Help here would be appreciated as well.




D417 D419 and D420 have all been removed, although I think this was premature on my part, since I assumed they were bad, based on these pictures I took of them:

*Looks like scorch marks, and no where else on the tin side of the board looks like this






* I followed this tutorial to test them and they seem to be in working condition after I removed them of course, stupid premature move on my part.





Both F401 and F402 are blown, and blow immediately when replaced and the TV plugged into the wall and turned on. This tells me either the Q406 has gone bad again, or it is another component for the fuses to blow immediately upon trying to turn the TV on.


I bought a pack of 10 fuses from eBay (here), instead of going with the "LittleFuse" OEM brand, I have a feeling I'll end up having to purchase the OEM brand again, just to be on the safe side.



I am totally open to trying to fix this power board via parts, but again, it all comes down to cost. If I'm going to spend close to $60 or more on parts, then I might as well get the power board. But again, who's to say the new power board won't experience the same problem as the one I have now.

So I'm asking for some help with this problem, as I don't know what direction to go.


If someone can help me out in regards to testing my Q406 transistor to see if it's still in working condition, I'd appreciate that. Any other input or suggestions is also welcome.


Thanks everyone-

[Mark L]

Re: Panasonic TH-42PX75U

I had another question I wanted to ask:

Upon desoldering the 3 diodes (D417, D418, & D420), I had a heck of a time with one of them, it seemed fused to the eyelet and would not come off the board. I pulled it with some needle nose pliers and one of the 6 eyelets came off with it. Are the eyelets an integral part of the circuit board? Do the serve a major purpose? I just want to make sure because this happened to 1 of the 3 eyelets from the Q406 transistor when I replaced it back in January. I can't seem to find any replacement eyelets and have no idea where to look. To my knowledge they're 1/16'' eyelets, but I'm also not sure what material they're made out of..... aluminum being my best guess.

Those with circuit board experience, are there any brands you'd recommend for soldering/desoldering irons? I have a 15 watt and 40 watt soldering iron from Radio Shack and a 45 watt Desoldering iron from Radio Shack that doesn't seem to be doing the job like it used to.

It seemed like the irons weren't hot enough to pool up the solder for me to extract it. I'm not sure if the OEM solder has a higher melting point than my irons could handle. Thus making the removal of the 3 diodes and the Q406 transistor that much more difficult.

Any help would be appreciated.

Thanks-

[tw2005]

Re: Panasonic TH-42PX75U

My first question is what material is in between the FET and the heatsink?

Something you can try in place of fuses is to connect 2 light bulbs in their place. I used 75W globes. I ended up doing this because I had the same problem with fuses blow straight away. The bulbs would glow bright indicating a short.

The resistor sounds open cct which is a casualty along with the fuses. It should read 10ohms. I blew all three of these several times.The rectifier could be bad. but something does not look quite right with the way that transistor is mounted. I just hope it's not cardboard or something that does not transfer heat.

test the bridge rectifier first and if ok I'd say that fet is shorted.

[Mark L]

Re: Panasonic TH-42PX75U

My first question is what material is in between the FET and the heatsink?

Something you can try in place of fuses is to connect 2 light bulbs in their place. I used 75W globes. I ended up doing this because I had the same problem with fuses blow straight away. The bulbs would glow bright indicating a short.

The resistor sounds open cct which is a casualty along with the fuses. It should read 10ohms. I blew all three of these several times.The rectifier could be bad. but something does not look quite right with the way that transistor is mounted. I just hope it's not cardboard or something that does not transfer heat.

test the bridge rectifier first and if ok I'd say that fet is shorted.

Thanks for the reply.

There is the silicone sheet between the FET and the heatsink. I left the same one that was on there before.

I tested the bridge rectifier and it is giving me the following readings:

Pic 1: .495

Pic 2: .502

Pic 3: .000

Pic 4: .000


When you say connect light bulbs, what do you mean? Do you mean reinstall the power board and turn the power on and hold a light bulb over the fuse casings?

How do I go about testing my FET transistor? What prongs do I hold onto the gate/source/drain?

Like I said before, I took out the D417/D419/D420 diodes off the board. I thought they were bad. Where can I get some replacements at? I haven't found any where on the internet.


Thanks

[tw2005]

Re: Panasonic TH-42PX75U

unless they're shorted or open cct i would not bother. SF38G 3A 600V Glass Passivated Super Fast Rectifier.

As for the FET, I have trouble with this too. I generally use the diode function check to see it is not completely open or shorted. i'm sure google will bring up an answer but there's more experienced folk here so I'm sure you'll get an answer. I don't have all the answers.

Do you have the service manual and can you follow schematics? This may help to check other components contributing to a short.

My problem was there was continuity between the centre leg of the fet and the heatsink which created a short. poor insulator between fet and heatsink(our mistake) I did not test the transistor for the original fault, someone else did that. I discovered my mistake by using another fet installed on the flip side for a quick test which worked and then blew up once mounted. Also blew a track which was concealed which i discovered once the fet was correctly mounted when no power at all.

A lot learnt from this.

I'd remove the fet and check it plus also I'd check for possible short on the same pinouts on the board just in case that's killing the fet.

With the bridge, is it 0 ohms across the -+ or OL(out of limit, or open) If 0 then suggests short and again I believe points to short on the FET if this was tested in cct.

Between fet center leg and heatsink there should be no continuity.

I can't help yu much more, I don't mind blowing up my own gear but don't want to give you a bum steer and hlp you blow your stuff up.

Your symptoms sound the same as I had when I had shorted the FET out that's all I can say.

As for the bulbs, I soldered leads to them and then solder those across each fuse. The filament takes the energy which would normally blow a fuse.

No I would not hold them, and don't electrocute yourself. It just helped me fault find it without forking out $ every blowup.

Good Luck

[Mark L]

Re: Panasonic TH-42PX75U

unless they're shorted or open cct i would not bother. SF38G 3A 600V Glass Passivated Super Fast Rectifier.

As for the FET, I have trouble with this too. I generally use the diode function check to see it is not completely open or shorted. i'm sure google will bring up an answer but there's more experienced folk here so I'm sure you'll get an answer. I don't have all the answers.

Thanks for the reply.

I accidentally broke one of the diodes when I removed it from the board.

I see the OEM part number is B0EAMR000009, but I only found one place online that carries them and they're out of stock. Plus they're $6.50 a piece!

So that attached file is comparable the OEM diodes?

Do you have the service manual and can you follow schematics? This may help to check other components contributing to a short.

I do have the service manual and have been using it while I test the components.

My problem was there was continuity between the centre leg of the fet and the heatsink which created a short. poor insulator between fet and heatsink(our mistake) I did not test the transistor for the original fault, someone else did that. I discovered my mistake by using another fet installed on the flip side for a quick test which worked and then blew up once mounted. Also blew a track which was concealed which i discovered once the fet was correctly mounted when no power at all.

I just went and checked my transistor for continuity between the center pin and the heatsink and I don't have any. So that's a good sign.

I'd remove the fet and check it plus also I'd check for possible short on the same pinouts on the board just in case that's killing the fet.

What do you mean by 'pinouts' and a short? I'm confused here.

With the bridge, is it 0 ohms across the -+ or OL(out of limit, or open) If 0 then suggests short and again I believe points to short on the FET if this was tested in cct.

It shows .000 on pins 1:4 with red and black both ways. No OL was given on the screen. This tells me most likely the rectifier is shorted.

As for the bulbs, I soldered leads to them and then solder those across each fuse. The filament takes the energy which would normally blow a fuse.

No I would not hold them, and don't electrocute yourself. It just helped me fault find it without forking out $ every blowup.

Oh ok, so you soldered wires from each side of the contact point on each fuse, then soldered the other 2 wires to the bulb itself? Did you solder onto the back side of the board I presume?

Then you plugged everything in and if the bulb lights up, that tells you the transistor is ok? Am I getting this right?


Thanks so much!

[retiredcaps]

Re: Panasonic TH-42PX75U

test the bridge rectifier first and if ok I'd say that fet is shorted.

Sorry to interrupt, but tw2005 gets 1 retiredcaps' bonus point award for a picture of your Australian Army issued Fluke 73.

Carry on.

[tw2005]

Re: Panasonic TH-42PX75U

Sorry to interrupt, but tw2005 gets 1 retiredcaps' bonus point award for a picture of your Australian Army issued Fluke 73.

Carry on.

Gee, thanks. I thought someone would be amused although it's ex Army and about 20year old.

Where can I read up on your Bonus Point Award Scheme?

[tw2005]

Re: Panasonic TH-42PX75U

That datasheet is for the exact diode installed as per what the schematic details.

I'm thinking the bridge is ok but there's a short elsewhere. was it tested on the board or removed?

If the bulbs light up bright it tells you there's a short, high current draw which would blow the fuse.

[Mark L]

Re: Panasonic TH-42PX75U

That datasheet is for the exact diode installed as per what the schematic details.

I'm thinking the bridge is ok but there's a short elsewhere. was it tested on the board or removed?

If the bulbs light up bright it tells you there's a short, high current draw which would blow the fuse.

The bridge was tested on the board.

As for the light bulb, you're saying to solder 2 wires from each side of the fuse (tin foil backside I presume?) and then onto the light bulb itself?

Then hook everything back up and run power?

[tw2005]

Re: Panasonic TH-42PX75U

The bridge was tested on the board.

As for the light bulb, you're saying to solder 2 wires from each side of the fuse (tin foil backside I presume?) and then onto the light bulb itself?

Then hook everything back up and run power?

Basically yes, as for the bridge I still think the problem is a short in cct not the bridge.

When i did the light bulbs with my short the relays would just continuously cycle on and off, bulbs flashing bright at turn on. I can;t remember now but I think I took the opportunity to measure the output of the bridge whilst it cycled power.

[Mark L]

Re: Panasonic TH-42PX75U

Basically yes, as for the bridge I still think the problem is a short in cct not the bridge.

When i did the light bulbs with my short the relays would just continuously cycle on and off, bulbs flashing bright at turn on. I can;t remember now but I think I took the opportunity to measure the output of the bridge whilst it cycled power.

CCT?

What does this stand for?

[tom66]

Re: Panasonic TH-42PX75U

CCT?

What does this stand for?

Circuit.

[cequil32]

Re: Panasonic TH-42PX75U

I am having a similar problem with my tv...can't seem to find the short though...I have a short over the 100 ohm resistor but can't tell if the bridge rectifier is shorter...I took the fet out of the circuit so this shouldn't be shorted. The 10 ohm resistor was blown and and I have replaced this. Do I need to take the rectifier out of the circuit to test it properly?