Investigating a Panasonic TCP46G25 Plasma TV - Page 1
Forum section: electronics / repair

author: vmallet
author_rank: Regular Contributor
timestamp: July 23, 2020, 11:39:58 pm
content: The device: Panasonic TCP46G25 46" Plasma TV, from around 2010The problem: device doesn't power on; flashes 4 pulses (= "Power SOS")The goal: find and hopefully fix the problem (in the power supply?)Service manual:https://www.manualslib.com/manual/836135/Panasonic-Tc-P46g25.htmlBecause the TV flashes its "Power SOS" code, I started investigating the power supply to try to find some obvious problem. I took the P-board (power supply) and A-board (logic) out and probed all the power rails (using test points on both boards) and they look about right (numbers below).I put things back together and then noticed the symptoms are a bit different depending on whether or not the P2 connector that connects the Vsus rail from the power supply to the SC board (Scan Drive) is connected. So we have these two situations:1) Everything connected (i.e. if I don't touch anything).Plug the TV into the wall. You can hear a relay click, ~12 seconds later the relay clicks again (performs some initial tests I guess?). Vsus stays at 0VPush the power button once: the relay clicks, Vsus rail stays just above 0V, then 1.5s later the relay clicks again and now the power LED flashes 4 pulses ("Power SOS")2) Same as 1 but just with P2 disconnected (i.e. Vsus doesn't get to the SC board anymore, but it still goes to the SS board via P11)Plug the TV into the wall. You can hear a relay click, ~12 seconds later the relay clicks again; Vsus stays at 0V (same as above)Push the power button once: the relay clicks, Vsus rail goes to ~210V, then 5.5s later the relay clicks again and Vsus starts its slow trip towards 0V (takes a couple of minutes to discharge the big output cap). Now the power LED flashes 7 pulses ("Driver SOS2")This makes me wonder if the problem might be in the SC board rather than the PSU, but the fact that the internal circuitry detects a PSU problem is not to be ignored.My next step is to try to see what I can find on the SC board and I wanted to fire off an email over here in case this problem sounds familiar to anyone. I searched the forum first but didn't find much on this topic.Note: most of these measures were taken in the first 10 seconds after plugging the PSU to the wall (i.e. set up my meter, check, plug into wall, read, disconnect from wall) except for those that needed to have the power button pressed to try to "turn it on".A-Board: TP3501 “STB5V” (A-Board 8/18 Schematic p54): 5.08VA-Board: TP3522 “F15V” (A-Board 8/18 Schematic p54): 14.9VA-Board: TP9196 “P15V” (A-Board 8/18 Schematic p54): 15.5VA-Board: TP3519 “+15V_S” for SOUND15V (A-Board 8/18 Schematic p54): 15.5VA-Board: TP5506 “SUB5V” (A-Board 8/18 Schematic p54): 4.98VA-Board: TP5606 “SUB5V_USB” (A-Board 8/18 Schematic p54): 4.99VA-Board: TP3506 “SUB9V” (A-Board 8/18 Schematic p54): 8.91VA-Board: TP9216 “P5V” (A-Board 12/18 Schematic p58): ~5V (didn't write it down)P-Board: TP9 “Vda”: 60.9VP: TP5 “Vsus”: ~210VHere are a couple of pictures just in case:

author: algorithm
author_rank: Regular Contributor
timestamp: November 29, 2020, 06:22:49 pm
content: Bumping this. Ive got the same TV and been struggling to get anywhere with it.I started off getting the 4 flash "SOS". Relays would click on but almost immediately click off.I could see voltage on power but the board lost it after the relays click off.Bought a replacement power board, it arrived broken into pieces. I patched the pieces but returned it afraid using the board in its state (bare solder patches on a screw mount) would be bad. So I tried to find the problem on the original board.Originally I couldnt find anything. But after returning the shattered board and reconnecting the old board, I got a different fault?The relays constantly clicked.Poking with the multimeter out I could see power going into R501 (if my eyes dont deceive me. the one right beside L601) but nothing on the far side. I tried to replace it. Innocently not expecting anything special after reassembly, upon plugging it in, out of the corner of my unsuspecting eye I saw a flash I can only compare to an arc from a welder. Still with plug in hand I yanked them apart. My cat bolted out of the room and I looked up to barely catch a glimpse of some magic smoke.After I saw that happen, I worried the arc was from L601. Not really sure how insulation on L601 did get compromised if so. but That was my fear.Ordered a replacement resistor and tried to replace it for a 2nd time. My dad assured me it wasnt L601 and against my better judgement I tried it. Same thing happened though. Flashed bright enough to leave a dot in your eye like looking at the sun.I tried testing the inductance, did see a difference. like 10mH on left side, but on right 11.3mH.Not really sure what I should be expecting to see.If anybody has advice for testing inductors/coils, or discovering shorts/compromised insulation? Would appreciate hearing. Thanks in advance.One thing worth trying I heard was unplugging boards to see if power supply stays on when w/e board is out?

author: Runco990
author_rank: Frequent Contributor
timestamp: November 29, 2020, 07:49:02 pm
content: The most common failure on Panasonic Plasma's are a short in the Y-Buffer board. This is often caused initially by loose ground screws that hold the boards in place.Pull the connectors from the Y-Buffers and measure ohms from ground to each pin on the panel connectors. Should be NO shorts.Since this IS the most common failure (I have several Panasonic Plasma's) I'd look there FIRST and work my way back.I have fixed a few..... Hope this helps. On Plasma's, it's not always the power supply... in fact, rarely.

author: algorithm
author_rank: Regular Contributor
timestamp: November 30, 2020, 11:43:11 pm
content: I appreciate the response runco, good advice too. I notice some solder joints that appeared to be cold (could see light through a hole on the pads connection) on the Y-Buffer board. Need to address that if I manage to get the psu back.In my discombobulated recollection previous, I forgot to mention, after it blew the resistor last, I tested the fuses and the F601 on the right side of input is broken. The "parts list" in service manual lists that as a "cartridge fuse". Took me a good while to find a pico fuse color band table to reference to be more exact (10A 250v).Also, when I unscrewed the board, some of the screws threads seemed to be somewhat darkened. While the screws were not loose while I dealt with it. I guess the screws were missing the shiny plating and charred from shorting to the chassis?Still oblivious as to what the correct protocol to testing/dealing with an inductor/coil with possibly/suspected exposed/missing insulation.I tried searching the internet for answers but just found results about cars.Would it be alright to just wrap the inductor with an insulation tape like kapton? Or would it need to be rewound or replaced?Also about testing the inductance? Should I be expecting the same amount of mH on both sides of inductor? Or is there no telling? lolThanks in advance

author: algorithm
author_rank: Regular Contributor
timestamp: December 15, 2020, 05:01:50 pm
content: So something funny, the resistor I took out of the psu was 62.4Ω according to color band? Same as in picture, but the service manual says "R501 M 412KOHM, 1/10W"Adding to my confusion. Still unsure about testing the inductor.

author: Runco990
author_rank: Frequent Contributor
timestamp: December 15, 2020, 09:13:01 pm
content: I wouldn't worry about the inductor for now if it shows continuity. Make sure the solder connections are good, though.The darkened screws aren't from "shorting"... it's from arcing. The screws SHORT the grounds through the panel backplane. When they get loose, they arc. The high voltage finds it's way to ground some other way, and the set dies. ALL the screws that mount the boards to the panel must make good contact. See the conductive strips in some places? All grounds are run through the panel itself.Measure each rail as you try to turn on the set. If you get a blip, it's likely fine. If you find one that does not try to come up, unplug the power line to the y sustain, etc. If it tries to come up but shuts down (protection) the power is likely fine.The most common failure is a short in the y sustain boards. Don't micro focus on one thing. Do the coarse power test and see if a rail is missing OR shorted. You can also ohm out the big power rails to the x and y boards for hard shorts.

author: algorithm
author_rank: Regular Contributor
timestamp: December 15, 2020, 09:50:36 pm
content: Ok, thank you again RuncoSo that helps explain a lot to me, but here is the thing concerning to me, those screws were still shiny when I took them out prior to the replacement resistors exploding, notably after the 2nd time. But the screws in the entire machine were tight. So Im perplexed how it would happen.I take it I need to replace those screws now as well?

author: Runco990
author_rank: Frequent Contributor
timestamp: December 16, 2020, 05:01:37 am
content: The screws are fine as long as they are good and tight. If yours were, then the failure is/was caused by something else. I was simply pointing to a common KNOWN failure CAUSE for many Panasonic Plasmas. The ground screw issue even had service bulletins as well as "Kits" with new screws with star washers to ensure they never loosened with thermal cycles. This is actually a preventable death, by simply checking a set and tightening the screws every few years.I even did it on my Kuro.My advice, when I give it, is usually based on common things to look at first (and eliminate) before going in depth with complex troubleshooting. I always try to start simple.It sounds like your trouble is probably elsewhere, but always check power and grounds first.Look for shorts on all power rails and unplug connectors to check for shorts. I may not be able to fix an Agilent 34401A just yet, but I HAVE fixed a lot of flat panels. Start simple and try to confirm what board the problem is on, THEN dig into that board. Power supply is rare on Panasonics but the driver boards are common failure. I trend to try to eliminate those first and foremost. The fact that you get blink codes is usually a sign that the power and system boards are LIKELY ok.Pull the big power connectors on the Y-sustain (Vsus on your set) and see if there is a short. Then check if power TRIES to come up (cable disconnected) on that rail when you try to turn on the set. Usually it will "blip" up and then shut down because of the various protect systems. You are looking for that blip that the power rail is in fact trying to start. If it DOES, it's usually fine.Yes, it could be the power supply, but try to eliminate the obvious known failures first. I forgot to mention, ALSO pull and re-seat ALL ribbon connectors, another common source of weird problems with these sets. Only after doing the simple stupid checks, suspect the actual power supply. You are fighting all the protection circuits which can often give misleading results.Of course, there are good videos on youtube showing this process, so maybe watch a few.You REALLY want it to be only a Y-sustain or power board issue. Anything else is often not economical to repair.

author: algorithm
author_rank: Regular Contributor
timestamp: December 16, 2020, 12:18:07 pm
content: Thank you very much again runco. I appreciate your advice. Well Im waiting for the resistors and fuse to show up in the mail. When Im able to get those back to working order I will do the tests you suggest and report back.I tested the Y buffer board contact strips I could reach easily for shorts. Didnt get any, but also didnt test every strip. (The tv is taken apart with a barricade of other junk in front of it.)When I was first trying to fix the thing I tested diodes and transistors on the Y buffer board. Mostly near buffer board input where I saw seemingly cold/bad joints. Got a lot of constant beeps while testing.If those said components went bad, could that make the strips show shorts?Or would it only be shorted there from the buffer IC?Hopefully I can repair it. I really could use the tv. They dont make em like these anymore either.Plasma appeals to me because it has better response than most counterparts I can afford.Thanks again.

author: Runco990
author_rank: Frequent Contributor
timestamp: December 16, 2020, 04:29:03 pm
content: The buffer IC's are the most common failure on Plasmas. They can take out things with them. It takes only ONE shorted line to shut down the set.I have 2 commercial Panasonics. The type you used to see on shows or the news.True, they don't make them like that any more.But.... they aren't exactly cheap to run, either. Aaaand.... mounting 65" that weighs near 200 pounds was no joke.