Death & Resurrection of a Plasma Display

On Friday Feb 13 my plasma display (a Panasonic TH-42PWD6-UY) died. It simply wouldn't turn on. Hit the power switch, the LED would go green for about 2 seconds, then back to red and blink. The blink pattern was solid red, 2 dark blinks, solid red.

I searched the net and found a thread on the AVS forum that described a problem which at first appeared similar. This was a 5-7 blink code due to a failed transistor in the power supply. This problem plagued Panasonic plasmas made in late 2003. But mine was made in Feb 2004, had the upgraded part from the factory and didn't have this problem.

Next step was to download the factory service manual. At $13 (a 500 page PDF file) I figured it was a no-brainer to have. I learned that the 2-blink code referred to a problem in the display driver circuitry.

I took the panel out to my shop and opened it up. It wouldn't stay ON long enough to test the internal voltages. But I found that unplugging SC-20 (where the "D" board connects to the "SC" board) enabled it to stay on indefinitely. All the voltages tested OK within tolerances, and the dreaded "IC-551" had the right part number, so the power supply was likely OK.

On powerup, the SC and SS boards have LEDs to assist troubleshooting. Here is what happened:

  • powerup
  • SC-1 on
  • SS-1 on
  • SC-2 on, with a quiet audible hum
    • --- then an audible relay click
  • all LEDs off, power off

    • It appeared something was wrong with the SC board, which may also be either of its SU or SD daughterboards. The SU & SD daughterboards have a bunch of ICs on them and when they fail these are often melted or otherwise visibly damaged. But the SU & SD boards looked brand new. I disconnected them individually, then both, with no change in behavior. I also disconnected SC-20, the connector from the "D" board into the "SC" board. When I did this, power would stay on, though none of the SC LEDs lit up and the screen would remain blank.

    Now the manual says troubleshooting is tied to the LEDs on the SC & SS boards. If they light up, the boards are OK. If not, they are bad. But this is ambiguous - what if they light up and then shut off? This appeared to me to be some kind of failed internal check on the SC board, which then shut itself off as a safety precaution. All of this tended pointed to the SC board, part number TPNA-2867.

    Before buying a replacement SC board, I called a couple of electronics shops in the area.

  • The tech at Telesystems Electronics in Everett, WA never returned my calls.
  • The tech at Electronics Professionals in Everson, WA (360)966-3621 did return my call promptly. He advised that the rev numbers of the boards didn't matter - part TPNA-2867 should work regardless of the date or rev number. He looked up the part confirmed that the cost was about $500. And, he also said if he had this display in his shop, based on what I told him, he would replace the SC board. I thanked him. That shop will definitely get my future business.

    • A $500 SC board was not cost effective - it wouldn't necessarily fix the problem at all, and even if it did, something else might fail later on this 5 year old display. Also, prices on these displays have fallen to the point where I can get a brand new replacement for about $1k. Continuing to search, I found Discount Merchant, a place that buys broken plasmas from places like Costco, opens up and sells the parts. I bought a new SC board from them for $180 plus shipping, total just under $200.

    It took Discount Merchant over a week to ship it, and when it arrived it had a few minor issues. I had to carefully straighten a few capacitors whose leads had bent due to careless packaging, and I had to meticulously clean off sticker residue they had stuck to one of the heat sinks (using Goof-Off, a Q-tip and my fingernail). I thought to myself, "If this board actually works, this is worth it as it saved me from having to buy a new plasma."

    After that, I installed the new SC board, double checked all connectors, grounding, screws, etc., and powered it up. The LEDs stayed lit!! The screen was fixed!! I then retuned the internal voltages as per the "PCB Replace Quick-Adjust" procedure in the service manual. My plasma display was operational like new.

    NOTE: according to the service menu, my display had a total of 1,894 hours and 4,201 powerups since new. It may be 5 years old, but it's less than 4% of the way through the display's 60k hour service life rating. So over the past 5 years I've averaged 25-30 minutes of use per power-up, and about 1 hour per day. Sounds about right, as we mainly use it to watch the news (and lately, to play Wii).

    Perusing the AVS forum thread in greater detail, on page 28 I found several other people with this exact same problem. That is, not the power supply issue, but a failed SC board TPNA-2867. It is a shame that Panasonic would produce a screen with such great picture quality and long service life, then drive it with underdesigned electronics that all too often fail prematurely. However, to be fair, this problem is probably not unique to Panasonic - all manufacturers probably do this.

    I shipped my old board back to Panasonic and asked for the core/DUD fee. I've read that the fee is about $150 for this particular board. If they pay it, I'm only out $50, which isn't bad at all. I'll post here if and when I get a response.