Panasonic TX-P50U20E - Page 1
Forum section: electronics / repair

author: blauerscharik
author_rank: Regular Contributor
timestamp: January 27, 2024, 01:44:03 pm
content: Hi Guys,I got this TV that I'm trying to bring back to life.Error code: 10x blinkingI found the schematic at ElektroTanya:https://easyupload.io/pl1u3aAnd measuring I am not getting 15V after T201Now looking at T201 physically it has a crack in the iron core. Could that be the problem or how can I make sure it's nothing else?Does anyone have time to take a look. Thanks.

author: cte
author_rank: Regular Contributor
timestamp: January 27, 2024, 04:46:27 pm
content: A cracked iron core?The schematic looks pretty complex, lots of special parts. But for a start...Disconnect mains first (!), and check those parts on the P-Board (page 45):Q201 and Q202 (short?)R205, R206, R207, R208, R221, R222, R223, R224 (R too high?)D251, D451, D351 (short?)Q355 (short?)

author: andersthuresson
author_rank: Contributor
timestamp: January 28, 2024, 11:30:38 am
content: Can't remember ever seeing a cracked transformer core beforeI would start by power everything off and try to measure resistance in that transformer to check if any of the windings are broken. It would explain why you have nothing coming out from it.

author: blauerscharik
author_rank: Regular Contributor
timestamp: January 28, 2024, 12:35:42 pm
content: Quote from: cte on January 27, 2024, 04:46:27 pmI attached a picture.QuoteThose two mosfets I don't understand. I desoldered them and testing using the multi-meter it looks like they don't open. But when I use a power supply with 5v then they open and the voltage from S to D starts to rise until OL. That is not normal is it?QuoteThey all got like 342KQuoteD251 is good, D451 I only found on the SC-Board? Not on the P-Board, but also good. D351 is good.QuoteThat one is open all the time. From S to D. Is that the problem then?But then shouldn't I have 15V before the mosfet?

author: blauerscharik
author_rank: Regular Contributor
timestamp: January 29, 2024, 02:01:11 pm
content: So I desoldered the transformer and found 0.02Ohm of resistance on the primary which is obviously shorted.Now where can I find a new one?The parts list mentions it as: ETB39LJ12GADOn the transformer and the board itself it says other things, see pictures.

author: blauerscharik
author_rank: Regular Contributor
timestamp: January 31, 2024, 04:10:03 pm
content: Does anybody have any suggestions?

author: SeanB
author_rank: Super Contributor
timestamp: January 31, 2024, 06:59:46 pm
content: DC resistance is normal, remember this runs at 100kHz, so a check with an inductance meter would give a higher value.

author: wraper
author_rank: Unknown
timestamp: January 31, 2024, 07:17:29 pm
content: 99% chance this have nothing to do with transformer. Measuring nearly short is absolutely normal, what DC resistance do you think will a few dozen turns of thick copper wire? Not to say this transformer is in SMPS used for standby, if it wasn't working, you would not have anything blinking at all.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 31, 2024, 10:07:38 pm
content: wraper: If I'm reading the schematic right it isn't the standby supply.Measuring transformer windings for resistance is just about only any use for checking that a winging isn't open or in some cases finding the end points of a winding with intermediate taps, other than that it's not saying much for the state of the winding.As for the cracked core:Well they already have a gap, you don't want too much opening then you start loosing magnetic coupling, I've found that for cracked cores bringing the two ends into contact then taping firmly together or clamping lightly and letting superglue in by capillarity is usually good enough.Try getting T201 back to a semi-normal geometry and give us the secondary DC voltages on start-up. (They may peak at normal values before rapidly dropping when the fault is detected.)

author: blauerscharik
author_rank: Regular Contributor
timestamp: February 01, 2024, 02:10:46 pm
content: Well that kinda sucks.Measuring it against other transformers I have desoldered and laying around, I was expecting to measure something in the few hundred ohms.With that expectation I broke the transformer open just to see if I could find anything fishy in the windings. But I didn'tWell with that being said. I guess I just made sure that the TV is not coming back to life...but lesson learned.

author: wraper
author_rank: Unknown
timestamp: February 01, 2024, 02:17:06 pm
content: Quote from: shakalnokturn on January 31, 2024, 10:07:38 pmIt's not just for standby. I didn't see any dedicated standby PSU in schematic. It supplies STB power rails, and does not seem to have capability to be shut down, so must be the only supply used during standby.

author: blauerscharik
author_rank: Regular Contributor
timestamp: February 01, 2024, 02:29:00 pm
content: Quote from: wraper on February 01, 2024, 02:17:06 pmT501 is doing the STB+5V, as far as I could tell.

author: wraper
author_rank: Unknown
timestamp: February 01, 2024, 03:02:39 pm
content: Quote from: blauerscharik on February 01, 2024, 02:29:00 pmMixed up them, I thought this was ETB29... T501. Anyway, cracks in ferrite core are very unlikely to cause PSU malfunction. Especially like here when it's only on one side of E-core and other side is uninterrupted.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 01, 2024, 05:12:49 pm
content: I have at least one Panasonic PDP power supply hanging aroun in my junk, very doubtful I have the same model but if this TV is really important to you I could check if one has the same xfrmr reference.The other option is buying a spare core.

author: blauerscharik
author_rank: Regular Contributor
timestamp: February 02, 2024, 04:24:41 pm
content: Quote from: shakalnokturn on February 01, 2024, 05:12:49 pmNo no it's not important to me. I just like picking up broken electronics for free or cheap and try to fix them or learn how they work.