Panasonic TH-42PA60A Plasma Repair

[mangozac]

Hi All,

These forums are a wealth of information on electronics repairs and usually I can get by with just reading them to get the answers I want. But not today

My background: professional electronic engineer designing and manufacturing niche control equipment. Consumer electronics are a whole different ball game, but I can certainly follow repair guides, measure voltages and read schematics to diagnose at a board level.

The TV: The TH-42PA60A is a 2005/2006 Panasonic plasma that as far as I can tell was only sold in Australia under that part number. It was my Grandmother's and after she passed away I acquired it. A year ago it had a P board (power supply) failure that was easily (and relatively cheaply) fixed by replacing the P board. I have the full service manuals and diagnostic flowcharts which are very handy.

A few weeks back we had some extremely wet weather and insanely high humidity for a few days and the TV gave up. Should have had it covered up. I was watching it in the evening and suddenly the picture developed a bunch of line patterns across it. I decided to turn it off to be safe. Tried to turn it back on and she was dead - no PSU relay clicks or anything. Diagnostics proved that STBY5V was available but the DG board was not sending the wake up signal to the PSU. According to the manual the solution was to replace the DG board, part number TNPA3756.

I did try cleaning the board using PCB cleaner and suitable brushes first but that was no help.

So I ordered a replacement DG board and it arrived just yesterday (from the UK). I plug it in and switch on power. We have relay clicks! But the picture doesn't come on. After a few seconds the power LED starts flashing a single blink code (which means "No particular check point" - handy). I did some research and apparently the other reason for a single blink is that the replacement board may be programmed for a different TV, hence why part number suffixes are important.

Suffixes? Dammit!

So I have a look at my two boards. The old one has a suffix "CQ" and the new one has suffix "CH". Other than that the only difference between them is that the new board has two HDMI ports whereas the old one only had a single. So I need to get one with the right suffix then.

I did some googling and it seems that used CQ suffix boards just aren't around. None of the used parts suppliers (local or international) even list them. I got a quote from a local parts supplier and they want ~$250 for a new board. It's not worth repairing at that cost.

I really don't want to have to bin this otherwise great TV (it's a great picture and everything else is in good condition) so I'm now clutching at straws. I've come up with one last resort:

As far as I can tell, the problem is that the MICOM Processor on the DG board (IC11003) doesn't like communicating with the other boards in the TV due to firmware/version differences. So if everything else on the boards (other than the extra HDMI input) is the same, what if I just swap over the ROM chips used by the processor (IC1101)? Is there any chance that could work? Anything else I should watch out for? I certainly don't have anything to lose...

Thanks for reading - sorry for the long post

[tom66]

Re: Panasonic TH-42PA60A Plasma Repair

The major concern with doing that would be: is the plasma panel the same between the CQ and CH boards? Because there is usually more than one firmware ROM IC.

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

In response to your question Tom I did some research and the CQ and CH variants are both used with 42" panels. As best I can tell the only differences really are the firmware and the extra HDMI port. As far as I can tell there is only the one ROM on the DG board, so replacing it should have the DG board running the firmware that the TV requires.

In any case I did the swap tonight. The ROM chips aren't a super fine pitch so it wasn't too bad using a standard pencil iron and some solder wick. I inspected all of the joints afterwards and all looked good.

I powered the TV up and the single blink code was gone. I pressed the power button on the remote and nothing happened. When I pressed and held the remote power button briefly the TV powered up. The panel lit up to all black and the LED indicators on the SS and SC boards came on. But there's no picture. The power LED did not turn on green (but the red turned off).

According to the service manual this would indicate a problem with the D board. Of course the issue here is that I could just end up chasing my tail if it's actually being caused by my little ROM swap hack. Is there anything else to try or should I just quit before I go throwing too much money and time at it?

[tom66]

Re: Panasonic TH-42PA60A Plasma Repair

Try holding:
VOL- on the set
MENU on the remote

while on the dark screen. Do you see a diagnostic screen? Any errors?

Usually panel discharge (priming glow, or black level glow) indicates a fault with the DG board, or A board, if this set uses one.

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

No joy. Also tried vol- and recall (as suggested in the service manual) with no result. This TV has a DG and H board rather than a combined A board.

So you think this is still a DG board issue (rather than D board)?

Thanks a lot for your help!

[tom66]

Re: Panasonic TH-42PA60A Plasma Repair

I do think it is the DG board. However, I cannot be certain.

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

OK I'll keep that in mind and do some more testing with the DG board. I'll see if I can find a service manual with the CH suffix board so that I can do an exact comparison and check there are no other differences I need to correct...

[tom66]

Re: Panasonic TH-42PA60A Plasma Repair

I have two documents available.
http://www.tgohome.com/ServiceManual...&Search=Submit

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

I have already been using your site and I must congratulate and thank you for such an awesome resource! Do you accept donations?

Thanks for the links - although they don't contain the CH variant, they do contain others such as CT, CC and CJ. The only physical differences are optional features such as the extra HDMI port or connection to an XV (digital tuner/card reader) board and related extra signal switching and routing.

While looking at the schematics one further possibility grabbed my attention: the DG board contains two serial EEPROMs. I only swapped over the flash ROM used as program memory (IC1101). The MICOM processor also has a 256k EEPROM attached to it (IC1102) which could hold all manner of configuration settings crucial to the board working.

I notice on the schematics some codes written next to the ROM (flash and EEPROM) chips. The one next to the flash chip on the schematic corresponded to the code printed on a sticker on the flash chip of my old DG board so I assume that these codes are data file names to be uploaded to these chips during assembly. The schematics have different codes for each of the variants!

So I'll swap the MICOM EEPROM chips over tonight and see what happens.

There is one other serial EEPROM on the board (IC4023) that is connected to the HDMI I/F chip (IC4026). I don't know what settings it will hold but since IC4026 is the same and the EEPROM has the same code "TVRN918" written next to it on all variations I think I'll just leave it.

Component level repairs - now this is where I have fun! It's so cool studying the schematics and learning how it all connects and works

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

Success!

It seems that the EEPROM does indeed store information critical to the correct base operation of the TV. Once the correct EEPROM was swapped in she powered up first go! To say I'm pleased would be a massive understatement!

When reading through the service manual I did see mention of an enable for 2 HDMI ports within the service mode screens. Since the new DG board has 2 HDMI ports I figured it'd be worth playing with that setting to see if I could activate the second one. Unfortunately it didn't have any effect and I can still only see/select one HDMI port on the AV menu. Oh well no drama.

There is only one thing I noticed: the power LED isn't lighting up green when the TV is on. I guess it should be pretty easy to probe the G_LED signal to find what's going on but it's really not bothering me that much...

Again thanks for your help Tom!

[tom66]

Re: Panasonic TH-42PA60A Plasma Repair

Great to hear.

If by donation you mean files... sure... PM me. Or money that goes on rent .

I'm very glad you got it working. Regarding the second HDMI port, it's possible you need to enable the visibility in the menu? I have a Panasonic plasma here and you can hide inputs as well as rename them. Worth a shot, I suppose.

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

I couldn't find anything about HDMI visibility on any of the standard menus. The menu system is pretty sparse...

PM incoming!

[mangozac]

Re: Panasonic TH-42PA60A Plasma Repair

I just wanted to follow up on this for the benefit of anybody else who goes down this route.

So last you heard I thought I had fixed the TV and indeed the AV inputs were working. But when I plugged in my media player into the HDMI port I got nothing. So after a bit more digging and pouring through the schematics I discovered the problem: the TNPA3756 boards have many other subtle differences between suffix versions than just ROM data and components for an extra HDMI port.

In fact the reason the power LED wasn't working as mentioned in a previous post is that there is even a different pin for driving the LED on the main MICOM processor! The other major difference is the inclusion of a few CMOS bilateral switches used to route the I2C serial communications signals that the processor uses to communicate with the audio and video data switches.

My solution: to make the CH board a CQ board by swapping and rearranging components. I had to inspect every component on the board and spot the differences. It took a long time with a fine soldering pencil and tweezers but in the end I finally got everything changed over.

So I can safely say that NOW the TV is completely fixed and functioning correctly!

Lesson for the day: take note of suffixes!