STB3.3v = 0.4V on Panasonic p42v10

[rvanpruissen]

Hi guys,

Recently I've been given a faulty Panasonic p42v10. The symptoms are as follows:

• No response when on power
• No standby LED
• No relay clicks

After some research, I found out that:

• STB5V rail is measuring 4.5V (just within tolerance?)
• STB3.3V rail measures 0.4V.
• STB3.3V has a resistance to ground of 4.2ohm with no cables connected to the board (A-board).

At this point I'm not sure how to proceed as there are many components connected to the STB3.3V rail, all of which could be shorting to ground.

Any help is appreciated!

Cheers, Rick

[Agent24]

Re: STB3.3v = 0.4V on Panasonic p42v10

Where does STB3.3v come from? PSU directly or derived from a secondary regulator on another board?

Can you put up some photos?

[rvanpruissen]

Re: STB3.3v = 0.4V on Panasonic p42v10

There's a regulator on the A-board (IC5480) which supplies the STB3.3V, based on the STB5V. I've included some pictures:

• 409: Overview
• 408: A-board component side
• 412: Close-up of IC5480
• 413: A-board foil side
• 414: Close-up of IC1100 which is should be powered by STB3.3V (among others

Meanwhile, I've found out that when I disconnect A3 connector (to D-board) and leave the rest plugged in, the TV powers up: relays click, backlight is on but still no standby light. At this point, STB3.3V becomes 0,67V (less load I suppose).

[Neelix]

Re: STB3.3v = 0.4V on Panasonic p42v10

Service manual -

[Neelix]

Re: STB3.3v = 0.4V on Panasonic p42v10

You're measuring 4.2 ohm between STB3.3V and GND which is far too low. One or more parts on the STB3.3V supply line is shorted and pulling the STB3.3V down. That's why you're only measuring 0.4V. You must find out which part. Start by removing L5480 from the A board and then measure the resistance between STB3.3V and GND again

[Neelix]

Re: STB3.3v = 0.4V on Panasonic p42v10

The parts on the A board can be tiny and easy to loose. So be careful

[TVRepairNoobie]

Re: STB3.3v = 0.4V on Panasonic p42v10

Hi rvanpruissen,

Test D503 on the P board to see if its open or closed. It is shaded green at the lower center.

[TVRepairNoobie]

Re: STB3.3v = 0.4V on Panasonic p42v10

When A-Board is not connected, you will not be able to power on the TV. At least this is my case with TC-P42S1 model. (no LED indication at all).

[rvanpruissen]

Re: STB3.3v = 0.4V on Panasonic p42v10

Thanks guys! I'm baffled to see that D503 measures open both ways, using the diode tester on my multimeter. Could this be the source of the problems? Or am I doing something wrong (sorry, sometimes I'm missing some basic electronics skills )

To fix the A-board, I think I'll go with Neelix' plan to remove L5480 first and test whether IC5480 itself is shorted to ground, or the short is somewhere in the rail. Not sure about when though, bit busy now.

Keep em coming please!

[rvanpruissen]

Re: STB3.3v = 0.4V on Panasonic p42v10

Crap. Just took a look at the schematic and D503 is parallel to a transformer, so thats what I'm measuring. Any particular reason to believe it's D503 TVRepairNoobie? Otherwise I won't try to get it out of the board. Thanks again!

[TVRepairNoobie]

Re: STB3.3v = 0.4V on Panasonic p42v10

rvanpruissen, I am a newbie (4 x TV fixed) working on a similar TV (TC-P42S1). The D503 is shorted when in circuit mine measures exactly the same. But I don't think it should be open thus, I suspect D503 might be faulty.

Hopefully, the experts here can shine some light in this matter.
If the diode on D503 is bad, I cannot find replacement for it anywhere. Diode has the follow label: T3D 97 or T 3D 97

[ReeceyBurger123]

Re: STB3.3v = 0.4V on Panasonic p42v10

If the diode tests open both ways its shorted, desolder and test it out of circuit.

[ReeceyBurger123]

Re: STB3.3v = 0.4V on Panasonic p42v10

rvanpruissen, I am a newbie (4 x TV fixed) working on a similar TV (TC-P42S1). The D503 is shorted when in circuit mine measures exactly the same. But I don't think it should be open thus, I suspect D503 might be faulty.

Hopefully, the experts here can shine some light in this matter.
If the diode on D503 is bad, I cannot find replacement for it anywhere. Diode has the follow label: T3D 97 or T 3D 97

There should be more numbers like 50n60 or something similar.

[Neelix]

Re: STB3.3v = 0.4V on Panasonic p42v10

For D503, have a look at this thread - https://www.badcaps.net/forum/showthread.php?t=17969

[budm]

Re: STB3.3v = 0.4V on Panasonic p42v10

The Diode is the back to back snubber diode network to clamp down the back EMF, you cannot use Ohm mode or Diode mode to test it, you have to supply enough voltage to reach the breakdown Voltage.
https://cdn.badcaps-static.com/pdfs/...386e62dcd7.pdf
page 4

[rvanpruissen]

Re: STB3.3v = 0.4V on Panasonic p42v10

Thanks budm. A bit out of my league though I have no reason to think this diode is bad, so I'll focus on the STB3.3v line first.

[rvanpruissen]

Re: STB3.3v = 0.4V on Panasonic p42v10

Ok guys. So after removing L1100 I've isolated the problem to the STB3.3V supply to IC1100, see attached image. The caps indicated in yellow are the ones I've removed so far and still there's only 4.2ohm resistance between this part of the STB3.3V line and ground.

Any brilliant ideas for the next step or should I assume IC1100 is shorted? I'm thinking maybe the crystal's capacitors on the right, or even further down the lines coming from IC1100.

Please help this electronics noob on his epic journey

[Agent24]

Re: STB3.3v = 0.4V on Panasonic p42v10

If there is nothing else connected to the STB3.3V rail, you have removed all the capacitors, then logically it would point to IC1100 being bad. But you must be sure there is nothing else you have missed, because it doesn't look like that IC will be easy to get if it is bad.

[rvanpruissen]

Re: STB3.3v = 0.4V on Panasonic p42v10

Could the short also be on one of the 100 connection of IC1100 I didn't 'disconnect'? Or is it unlikely there's an internal connection between the 4 IVDD STB3.3V connections and the rest of the connections.

Any suggestions on where to check next? IC1100 is indeed difficult (impossible?) to find (and replace).

[Agent24]

Re: STB3.3v = 0.4V on Panasonic p42v10

I don't think there is anywhere else to check. If the problem is between L1100 and IC1100 and you have disconnected the capacitors it is very likely IC1100 showing that 4.2 Ohms.

It seems it's just a microcontroller, so as far as I can tell there should be no low resistance paths between its power pins and anything else, it's not like it's doing any heavy current switching or anything.

It seems odd that a microcontroller would go shorted, so it's also possible the PCB itself has the short (can happen if there's been physical damage), or there's a solder ball under the IC or such.

If you have the tools (hot air etc) and can remove that IC, check for solder balls\bridges\whiskers. See if that 4.2 Ohms is still on the IC out of circuit. See if it's still on the board with the IC removed.

If the IC seems OK out of circuit and there is no 4.2 Ohm short on the board, it may have been a solder bridge. Resolder the IC and see if it is fixed.


Otherwise, try to find a new IC or replace the whole board I guess... unless someone else has any other clever ideas.