Panasonic TH-42PX25 Digital HD Plasma dead

[Quasar]

Found on the curb. 5 year old unit. Owner stated it blinks the power indicator 12 times and Panasonic said it was power supply related. Estimates from 2 shops had it around $300 for repair.

Have the remote (a super bonus) and the owners manual. Wow! You need the book and the remote as this is a multifunction set with split-screen and PIP and lots of other goodies.

Needless to say, it is a bear to move.

I have not fired it up at this point, but I'll do that later, after my back recovers.

Questions:
1) Can I leave this on its stand and take the back off to work on it, or do I have to lay it down? I have a no room to leave this lying down.

2) Does the blink code make sense and does anyone have an answer as to the failure going from that? Is this a common enough failure that someone has seen before and knows where to go looking?

3) Is there a diagnostic/technician mode combination to enter on the remote or elsewhere that will assist in determining the problem?

Thanks in advance!

Q

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Found on the curb. 5 year old unit. Owner stated it blinks the power indicator 12 times and Panasonic said it was power supply related. Estimates from 2 shops had it around $300 for repair.

Have the remote (a super bonus) and the owners manual. Wow! You need the book and the remote as this is a multifunction set with split-screen and PIP and lots of other goodies.

Needless to say, it is a bear to move.

I have not fired it up at this point, but I'll do that later, after my back recovers.

Questions:
1) Can I leave this on its stand and take the back off to work on it, or do I have to lay it down? I have a no room to leave this lying down.

2) Does the blink code make sense and does anyone have an answer as to the failure going from that? Is this a common enough failure that someone has seen before and knows where to go looking?

3) Is there a diagnostic/technician mode combination to enter on the remote or elsewhere that will assist in determining the problem?

Thanks in advance!

Q

http://elektrotanya.com/?q=showresul...oria=&kat2=all

As far as working on it, most of the sets I have worked on require you to pull the stand before pulling the back. All of them will allow you to put the stand back on and stand the TV up to work on it.

Yes, they are heavy. Servicing plasma TVs is not a job for wimps. Sorry to hear about your back.

PlainBill

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Thanks for the links PlainBill

Update:

When plugged in, a click is heard inside.
When powered on, a louder click is heard and the screen flashes quickly.
The power LED blinking is: Steady On (3 seconds) - 11 blinks, then repeats.

Q

EDIT:
According to the SM, that indicates Tuner Power.

They also call it 12 blinks as they count the "off" cycles, not the "on" cycles.

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

I got the back off and cleaned it up with a vac. Did a visual and see nothing burnt or obviously wrong. Probed for some voltages and found a 5vstby that seems correct. The other connectors to the power board have no means of measuring at the pins. Only the 2 going to the SC (Scan Drive) and SS (Sustain Drive) boards are capable of being probed.

I do have a small red LED lit continuously on either the DG (Digital Core) or DT (ATSC Interface) board when plugged in.

Various readings across the Power board on assorted jumper wires were done just to see if anything was showing up. I can not get any readings of significance as the units' cycle is much too short. Its relays click a few times then it is all done and starts flashing the power light.

Disconnecting the SC & SS plugs make no difference in the actions or results.

Testing of caps all proved they are fine (Pannies and Rubies). None of the transistors or diode packs show any problems. I'm going back across now to do some smaller diodes and miscellany. There are SMD's on the back and I'll see what they reveal. Several IC's of both through-hole and SMD type.

Suggestions from the TV gurus, please.

Q

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

If the error code indicates a problem with tuner power either start examining the schematic of the appropriate board or replace the board. If this is anything like any of the other TVs I've seen there are several DC-DC converters on every board. It's time to start looking at where the tuner gets it's power.

I downloaded the service manual; it's not set up the way the other Panasonic manuals were. If you haven't already done so, find the file called 'Navigator', double click on it to open it in your browser.

It APPEARS the H board is the one of interest.

PlainBill

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Yes. I did find the Navigator file. This is a very complex set.

I don't follow your reasoning why H, the Rear Terminal Input Board, would be a suspect? Please explain.

The PF board creates 10v and 24v which is fed to the PA board and then on to the P board as 5vstby. It is then fed back to the PF board to engage the 1 relay that I hear click when I plug the unit in. Two (2) other relays are on the P board which work in unison with each other in that both supply the Line side of power to the P board. When the power button is pushed, Relay 1 engages and sends Line power through a bank of 3 low ohm power resistors. A second or so passes then you hear Relay 2 click as it bypasses those resistors. Relay 1 then cuts out, and power is supplied through Relay 2 directly from the Line. As the symptom presents itself, Relay 2 cuts out after a second or so, which seems to indicate the system has faulted and caused shutdown. It seems as though P never gets a chance to come fully up before Relay 2 cuts out and shuts the whole thing down, sans 5vstby.

As I said, disconnecting the SS/SC connections to P does not change this, which seems to indicate the fault is not in those boards. Thankfully. They look like a great deal of work to remove as they are connected to SU, SD, SS2, SS3, and feeds to the screen panel. I see nightmare.

I was looking more towards PA (DC/DC, Audio), as it seems every other connection seems to go there from P. But, I have to unwind the wiring bundle more to see for sure.

I have walked across the P board more completely and have not found any component questionable. This does not exclude the IC's, as I will need power to see if they are functioning.

I noticed the 4 fans do not even pulse when power is applied. They are all connected to the PA board. I also see what looks like a video card cooling fan down in the DT section.

Is there some way to bypass the shutdown to see if I can keep voltage long enough to get some measurements and get a clue as to the trouble?

Q

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Yes. I did find the Navigator file. This is a very complex set.

I don't follow your reasoning why H, the Rear Terminal Input Board, would be a suspect? Please explain.

The PF board creates 10v and 24v which is fed to the PA board and then on to the P board as 5vstby. It is then fed back to the PF board to engage the 1 relay that I hear click when I plug the unit in. Two (2) other relays are on the P board which work in unison with each other in that both supply the Line side of power to the P board. When the power button is pushed, Relay 1 engages and sends Line power through a bank of 3 low ohm power resistors. A second or so passes then you hear Relay 2 click as it bypasses those resistors. Relay 1 then cuts out, and power is supplied through Relay 2 directly from the Line. As the symptom presents itself, Relay 2 cuts out after a second or so, which seems to indicate the system has faulted and caused shutdown. It seems as though P never gets a chance to come fully up before Relay 2 cuts out and shuts the whole thing down, sans 5vstby.

As I said, disconnecting the SS/SC connections to P does not change this, which seems to indicate the fault is not in those boards. Thankfully. They look like a great deal of work to remove as they are connected to SU, SD, SS2, SS3, and feeds to the screen panel. I see nightmare.

I was looking more towards PA (DC/DC, Audio), as it seems every other connection seems to go there from P. But, I have to unwind the wiring bundle more to see for sure.

I have walked across the P board more completely and have not found any component questionable. This does not exclude the IC's, as I will need power to see if they are functioning.

I noticed the 4 fans do not even pulse when power is applied. They are all connected to the PA board. I also see what looks like a video card cooling fan down in the DT section.

Is there some way to bypass the shutdown to see if I can keep voltage long enough to get some measurements and get a clue as to the trouble?

Q

Hello!!! The error you are getting indicates a problem with the tuner supply.

The following is an outline of how the Philips SSB works. When power is applied to the TV 5vSTB comes up, the Standby processor starts. When the power button on either the remote or the front panel is pressed the main power relay closes. The Standby processor then starts to check the various supply voltages, initializes various other processors, etc. If it encounters an error it will shut down the main power supply and flash an error code.

I've dealt with several plasma TVs that had power issues, on two of them the time between power on and power back off was in the range of 2-3 seconds - barely long enough to get a voltage reading.

Now, I understand, you are dealing with a Panasonic, not a Philips or LG, but the guys who designed this didn't design the error codes to lead you off in the wrong direction. To me the easiest step is to check the voltage inputs to the tuner and see if they appear to come up properly. If they do, then it is time to figure out WHY the Standby processor is giving you bad information.

I know I'm repeating myself, but I STRONGLY suggest you look for Panasonic Plasma Training Manual I'm sure I saw one manual there that gave troubleshooting information on the power supply.

PlainBill

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Thanks for the explanation. Now, if I could only locate the T board. The "Service Hint" from Navigator that shows the board layout, does not show its location...? Do they perhaps mean the TB board, who's designation is not called out in the board list?

"I'm sure I saw one manual there that gave troubleshooting information on the power supply."

Where?

There is a dtforums on a Google that lists it, but it doesn't download.

Q

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

I got down to the H board which has a metal encased "IF"? component plugged into it which would be the TB componet mentioned before. All is covered by the DT module.

If the problem lies on the H board, then it's well above my pay grade to deal with it. All SMD and multi-leaded IC's.

Now, the only bundle of wires connecting it to the rest of the set comes directly from the PA board (DC/DC, Audio).

So, given your experiences, do you think the problem is on the H board, or the PA board which supplies it? I think I can get readings from the connector coming off the PA board, although I may have to use a pin to get into it.

Q

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

I got down to the H board which has a metal encased "IF"? component plugged into it which would be the TB componet mentioned before. All is covered by the DT module.

If the problem lies on the H board, then it's well above my pay grade to deal with it. All SMD and multi-leaded IC's.

Now, the only bundle of wires connecting it to the rest of the set comes directly from the PA board (DC/DC, Audio).

So, given your experiences, do you think the problem is on the H board, or the PA board which supplies it? I think I can get readings from the connector coming off the PA board, although I may have to use a pin to get into it.

Q

First, http://cgi.ebay.com/Panasonic-TH-42P...-/350261466368

Next, I have found that most connectors have enough clearance that a dissecting pick or even a straight pin can be slid in between the wire and the connector to get a voltage reading.

Replacing 8 - 16 pin SMD devices is easy if you use Chip-Quik, then clean up with solder braid.

PlainBill

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

PlainBill,

Just a step outside of this discussion, but it's a local set up for $75. In your opinion, what might be involved? Is it worth the investment?

Panasonic TH - 4_2_PX_6_0_U (Spacing to keep searches from hitting a non-relevant post)

Q

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Now, on to the tasty bits-

Referring to file: s_pa_02.pdf under Navigator: 15.22 PA Board (2 of 2)

On the PA board I was able to check some voltages. If I just plugged the unit in and did not go to power-up, at the PA18 connector, I found 1.8v on 2 pins where the schematic says SUB8.3 on one side of the connector, and 3.3 on the other. Tracing this back to its source led me to IC7502 indicated as AVR 9V.

The other voltage found on PA18 was 10v and matches the schematic for 3 pins.

The 1.8v does not vary with power-up and failure, nor does the 10v.

Going back to IC7502, I found 24v on pin 1 and 2.4v on pin 5. Those are correct per the schematic. Pin 2 is the output and is steady at 2.4v. Pin 3 is ground and pin 4 is reading 0.4v or so. There is a 2 resistor voltage divider connected to pin 4 (3.92k & 806 ohms) and is what sets the control voltage for the IC. The math works, so that tells me the resistors are good. There is a 12v zener farther along that looks like it will clamp any surges.

IC7502 is wired for soft-on and appears that it should always be on as long as the 24v is present. One side of it is switched at power-up through Q7501 an 8 pin SOIC MOSFET, which is controlled by Q7502, a UN2214 (NPN EPT with resistor).

There are 4 more identical IC's on the board IC7501, 3, 4, 5 and they are all setup for power-on switching. I measured each one of those on pin 2 and they all output (for the one second the power comes on) at the correct voltages. 5, 5, 5, 2.5

It seems that the 9V is the problem here. The PA18 connector feeds the JA board which interconnects the DT & DG boards. The H board plugs into the DG.

The -switched- 9V goes to (or is supposed to) -
a) Vcc on IC7581 which seems to generate "BT30V" to the PA2 connector
b) the PA2 connector "MAIN9V(SUB9V)"
which then goes to the DG board.

Your thoughts.

Q

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

PlainBill,

Just a step outside of this discussion, but it's a local set up for $75. In your opinion, what might be involved? Is it worth the investment?

Panasonic TH - 4_2_PX_6_0_U (Spacing to keep searches from hitting a non-relevant post)

Q

I see two problems. IF the TV is tuned to an analog channel which is causing the snow, it's a non-issue. Certainly the menu fragment looks sharp.

That leaves the vertical bars, which could be either the lower buffer or the panel itself. Perhaps Wizard will know which is most likely.

The service manual is available on Electrotanya as a proper pdf. A number of buffers are available on eBay for as little as $30; I'm not sure which would be the proper one, you can do the research. The service manual is available on Electrotanya as a proper pdf.

It depends on what your time is worth, and what you want to do with the TV. Six months ago I could quickly sell repaired 42" plasma TVs for $400. Now I'm having problems selling one for $300. So do the math.

PlainBill

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Now, on to the tasty bits-

Referring to file: s_pa_02.pdf under Navigator: 15.22 PA Board (2 of 2)

On the PA board I was able to check some voltages. If I just plugged the unit in and did not go to power-up, at the PA18 connector, I found 1.8v on 2 pins where the schematic says SUB8.3 on one side of the connector, and 3.3 on the other. Tracing this back to its source led me to IC7502 indicated as AVR 9V.

The other voltage found on PA18 was 10v and matches the schematic for 3 pins.

The 1.8v does not vary with power-up and failure, nor does the 10v.

Going back to IC7502, I found 24v on pin 1 and 2.4v on pin 5. Those are correct per the schematic. Pin 2 is the output and is steady at 2.4v. Pin 3 is ground and pin 4 is reading 0.4v or so. There is a 2 resistor voltage divider connected to pin 4 (3.92k & 806 ohms) and is what sets the control voltage for the IC. The math works, so that tells me the resistors are good. There is a 12v zener farther along that looks like it will clamp any surges.

IC7502 is wired for soft-on and appears that it should always be on as long as the 24v is present. One side of it is switched at power-up through Q7501 an 8 pin SOIC MOSFET, which is controlled by Q7502, a UN2214 (NPN EPT with resistor).

There are 4 more identical IC's on the board IC7501, 3, 4, 5 and they are all setup for power-on switching. I measured each one of those on pin 2 and they all output (for the one second the power comes on) at the correct voltages. 5, 5, 5, 2.5

It seems that the 9V is the problem here. The PA18 connector feeds the JA board which interconnects the DT & DG boards. The H board plugs into the DG.

The -switched- 9V goes to (or is supposed to) -
a) Vcc on IC7581 which seems to generate "BT30V" to the PA2 connector
b) the PA2 connector "MAIN9V(SUB9V)"
which then goes to the DG board.

Your thoughts.

Q

DamnifIknow. You lost me at 'tasty bits'. I'll look at it later today, Faraday willing.

PlainBill

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Thanks on both posts. On the first, it's been up for nearly 2 weeks so no one has jumped at it. I got the PDF's for it. I was hoping to see if any parts could be robbed to fix this one.

On the second one, I've attached the schematic of the PA board DC/DC converter area that I referenced in the opening, so you don't have to chase it down.

Perhaps Wizard will join in with information on both sets.

Q

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

It bugged me that the 9V constant part of the supply was pulled down to 2.8. The 24v in was fine and I just can't figure why, going by the schematic. I went so far as to pull the 2 pins in the PA18 connector (7&8) where the one part of the 9v goes down to the JA interconnect board. Doing this allowed the voltage to come up to 3.1v. Now I am very confused, as there is no connection on that line that could load the regulator that heavily to cause a ~6v drop. The regulator is not running hot at all.

In a nutshell, one part is a constant supply of 9v that eventually ends up on the DT board feeding a 5v standby regulator (IC8055) - see: 15.44 DT-Board (7 of 8) pin 64 off the JA connector. Pulling the 2 pins removes that connection.

The other part of the constant 9v runs to the circuit around Q7544 through resistor R7536 a 470 ohm resistor and diode D7545 (reverse biased?). I am uncertain what this circuit does, but even a short to ground on the other side of R7536 would seem to be insufficient (20mA) to draw down the supply or fry the resistor.

So, I am left with the remaining path, the -switched- side through Q7501, that is not in play right now as the set is still in standby (just plugged in, nothing else). The 2.8 v is present at pins 1-3 but not at 5-8 until the power button is pushed. Pin 4's (gate) voltage rises with power on to 2.5v.

The experiment: (all connections/connectors restored to normal)

I hooked a 9v battery through a 47 ohm resistor to the output pin of the 9v regulator. Plugged the set in and attempted power on. Same failure. The resistor did get warm.

Then I removed the resistor and went direct. Used the ground on a jumper lead as the switch to the battery. Did power on and when I heard the 1st relay click, I grounded the battery negative. Viola! The set came on and ran steady.

BUT - No OSD of any type on any remote button push. There was an overall light blue color to the screen. The fans all ran, the red LEDs on the SS board were lit constant, and the power LED remained red. The battery started getting warm and after a minute or so, I disconnected it and the set immediately shut down.

I took some resistance measurements on the 5 identical regulators on this PA board. Although the results varied, none came as low as the 3.2 ohms I saw on the output of the 9v one. I pulled the board for bench examination.

Applying a 24v supply to the 9v regultor provided 9v!!! Now I am totally confused.

I did some component checking, especially the diodes in the Q7544 area. Everything checks out.

I'll reinstall the board and check this again. Something is very odd.

Q

{Additional: The 3.2 ohm reading (from ground to Pin 2 [output] of 9v regulator) appears when PA2 is connected. There are no other connectors plugged into the PA board. PA2 cable is connected directly to the DG board.}

[shovenose]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

is there 24v anywhere else where you could run wires to the 9v regulator? it sounds like the regulator isnt getting sufficient voltage, so you could find somewhere else where the 24 maybe DOES work?

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

I'm going to do a brief analysis of the situation here; I'm still struggling to grasp the details of what you have found.

Shoot, wasted a lot of time when I should have read more carefully. The load appears when PA2 is connected. As I read the schematic, 9V should not be going to PA2 when the TV is off; check Q7501 and associated components. You may have a double fault.

You do NOT want to replace the DG board.

PlainBill

[PlainBill]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

I glanced at the schematic for the DG board; it's complex. The 9V supply provide power to many of the on-board regulators. Either one of the regulators or a direct load is loading down the 9V power rail. Since the rail reads 3.2 ohms to ground, it is unlikely that the problem is a load on one of the regulators.

I note that there are actually two 9V outputs from this board - Main9V (PA2-15) and Main9V(Sub9V) (PA2-21,23). The first step would be to identify which of these has the low resistance. Then I would identify points in the schematic which can be opened to isolate sections. For example, on page 3 of the DC schematic L4501 can be easily lifted to isolate a portion of the board.

Alternatively, provide an auxiliary source of 9V, and check for regulators that have a low output voltage.

PlainBill

[Quasar]

Re: Panasonic TH-42PX25 Digital HD Plasma dead

Thank you for the reply and analysis.

Power has been restored, Cap'n!

Details and photos to follow.

Teaser: Problem was in the 30v line to DG that goes to H that ends up in TB.

------------------------------------------------------------------
New set of troubles:

With no input and with cable input:
- No picture
- Horizontal purple and green lines/bars
- OSD is clear and perfect
- Split screen functions but same lines/bars
- PIP functions but is B&W, not a complete picture, and grainy. It moves to the 4 corners when directed.
- Sound is good

Q