Re: Panasonic sc tnpa5081 rebuild
So after my last foray into trying to rebuild one of these I thought I would try one of the other dead boards I had gotten my hands on (this one had the "tradiditonal" IC773/Q661 failure). I was very careful to go over everything a few times.
Thought I had caught everything failed, plugged it in and a bit of a whine and then 7 blinks (LED comes on OK then slowly fades away after 7 blinks).
assumed I had blown everything again, but after a thorough testing everything seems fine except for PC461 which is ~shorted...
rockit711
Senior Member
Last Activity: 10-04-2021, 07:45 PM
Joined: 11-04-2015
Location: Adelaide, South Australia
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Re: Panasonic sc tnpa5081 rebuild
Thanks for the advice, yes have a 50v20a that obviously is now short a SC. I have read through this thread a few times and checked the parts where you and others have been stumped in the past and come up blank now.
Ive pulled out Q401&2 (dg502) they both test ok out of circuit. D401 &402 also test good once out.
it looks like the only (maybe?) casualties from the try were Q661 and D641, but ill probably replace the rest on that line too (the 30F125s and the other diode) just to be safe.
...Leave a comment:
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Re: Panasonic sc tnpa5081 rebuild
I tested them out of circuit. Having read through this thread already and seen a few of your comments stating that at least one of them seems to fail every time, I thought I would do a better test on all the "big" components than simply a short circuit test in case any of them failed in a way that wouldn't show in circuit.
I did resistance C-E (from memory I got ~2.4M one way and OL the other)
then I did the "turn on test" turning the gate on with a multimeter on diode setting while measuring resistance C-E...Leave a comment:
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Re: Panasonic sc tnpa5081 rebuild
Having my first try at a TNPA5081AF board
These are the parts that I isolated as failed the first sweep:
D16451 RF101L4S 400V 1A SHORT
D16482 RFN25TM4SW SHORT
Q16452 GT45G128 SHORT
Q16402 DG3D5020CSLW SHORT
Q16403 DG3D5020CSLW SHORT
Q16421 DG3D4020CSRP SHORT
Q16422 DG3D4020CSRP SHORT
Q16551 CPH5524-TL-E SHORT
Q16661 RJP63F3A SHORT
Q16660 R5007ANX SHORT
I wasn't sure about IC16521 (M81737FP), so swapped it given Q551 and D451 had failed.
...Leave a comment:
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Re: Samsung 60" plasma power supply issue - BN44-00514A
Bump. any ideas at all?Leave a comment:
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Re: Samsung 60" plasma power supply issue - BN44-00514A
After a bit closer inspection it looks like one of the secondary coils of the gate drive transformer has failed- the insulation was all melted and flaky and wasn't insulating anymore - I could getting a 0 ohm resistance reading by touching the probes on any points of the exposed coil. I assume this was another victim of whatever blew out the FETs, resistors and diodes originally.
I replaced the transformer with one that looks (visually) identical to it off one of the other power boards.
fired...Last edited by rockit711; 12-21-2016, 07:39 AM.Leave a comment:
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Re: Samsung 60" plasma power supply issue - BN44-00514A
OK, a bit of further information:
I tested the AC voltage across the gate driver transformer (primary side - UCC25600 side) and got a mere .6V momentarily. When I tested one of the other working boards with the same topology I got 7V here, so .6V doesn't seem right to me. does that mean the problem may be in the switching PNP/NPN combos or the zener diodes on this part of the circuit? or could it be the gate drive transformer?Leave a comment:
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Samsung 60" plasma power supply issue - BN44-00514A
I have searched already but despite many many promising threads on this and similar power boards I have been unable to locate anything that has done the same in previous threads.
The board was presented to me with no power outputs whatsoever and a few clearly blown components:
QS802 and QS804 were shorted and cracked open.
RS833 and RS815 had likewise blown apart.
DS810 had also blown the top off its casing (and was open)
DS808 had no visible signs of damage but was measuring open with a diode test.
the main fuse had also blown
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
check D112 (large diode on the primary side of the LED transformer circuit) it was a "FR307" on mine. it resulted in the same "flash" then nothing as you describe. May need to be de-soldered to get a good test on it. Also do a resistance check on it in case it has partially failed (as mine had).
If that isn't it then I'd recommend looking at pin 9 of the OB3354 chip (its the 16 pin SMD one just to the left of the LED connectors you have marked in your picture).
...Leave a comment:
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Re: LG 42LGX Mystery Part- at least to me;-)
The above worked for me, had a TV with the same board and the same symptoms (horizontal static lines) and after swapping over the 100uf 16v smd caps its now working properly.
I only changed the ones you can get at without removing the soldered on cover part (missed a few around the edge under the metal cover)
Unfortunately I didn't test the replacements one at a time so can't narrow down any further any specific ones that need replacing.Leave a comment:
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Re: is it possible for every LED in a backlight assembly to fail?
That did it, they were 6V! I didn't know about those....Leave a comment:
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is it possible for every LED in a backlight assembly to fail?
I'm trying to fix up a Palsonic 50" LED TV, I suspected a LED failure as all the symptoms were there (power comes up fine, image displayed but no back light, LED power comes up initially then shuts off quickly triggering the driver chips fault pin etc.)
Once I got the screen off there were obviously two failed LEDs straight up (clearly burnt out, black soot around them and melted plastic caps). but the rest look OK. However once I started testing them it appears that every single one has failed! the Diode test on the DMM didn't illuminate a single one, even slightly. The 2xAA... -
Re: LG 60PV250 - Erratic shut off
If the above doesn't bear any fruit then there's a pretty simple test that can help further diagnostics.
Most LG TVs have a Auto-on function, where the PSU and sustain boards turn themselves on without the mainboard connected (triggered by the "auto GND" pin on the PSU-mainboard power connector).
To try it unplug the mainboard (both power and the flat cable next to the power plug). It should power up and the screen should *very* dimly illuminate (it can be very hard to notice especially in a bright room...Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
its a FR307 - 1000V maximum DC blocking, 700V max RMS voltage. 3A rating.
I don't recall having seen the manufacturers logo before, its a black "R" (with white border) with a smaller white "S" or maybe "5" inside it (creating the holes at the top and bottom of the R) - don't know if that description makes any sense!
perhaps its just a cheap knockoff and doesn't actually meet the specs of the official FR307.Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
SOLVED!
the culprit was DIODE "D112" on the schematic.
Despite showing the correct forward voltage drop for the diode (.46V) under a diode test, and no measurement in reverse, it has ~1.3kOhm resistance across it. would have found it far earlier had I thought to do a resistance test over the diode despite the seemingly good diode test result!
now, seeing as the 2nd PSU is failing in the same way this diode may well be a weakness in the 55" implementation...Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
To revive this thread a bit with new information:
After putting this into the "too hard" category for awhile I was lucky enough to come across an identical TV with an "intermittent fault" that turned it off after a few hours and needed a few minutes unplugged before turning back on, decided it was worth the risk to buy it cheap as a diagnosis tool and potentially fix 2 tvs at the same time so got it.
so now for the updates:
Took the power...Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
Swapped out that LED with a good one off another string (actually tried 4 off two different good strings- just to be sure I hadn't damaged them in removal/replacement). ANNDD.... its still exactly the same as before
- everything is the same as far as I can tell, measured the various pins and as far as DMM measurements go its all operating exactly the same as with the "bad" LED.
I have also tested all the other LEDs for resistance, none of the others have a reading on the 2MOhm scale....Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
Is there any special glue or anything recommended for re-attaching the lenses?
Also what is BudMs method (or a link to where it is)? Tried to find it but couldnt see any thing obvious....Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
Well it didn't turn off for over a minute..
But then I went to test the next one in the chain (to check the current was still close) and got the wrong test point so it was putting the 3v over 2 LEDs, and oddly the 2nd (good) one illuminated very dimly..
Turns out the 1st led has indeed failed, has a measurable resistance across it, ~300kOhm. Probably failing totally at peak current output.
Still no idea why it isn't triggering the drivers protection though.
Will...Leave a comment:
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Re: "Dick Smith" 55" LED backlight issue - model GE6880
Before i go popping off lenses and desoldering LEDs, is there any way to use the test points (they were nice enough to put one on either side of each led)? Would soldering in a second LED with wires to the test points work for testing purposes? Or perhaps a resistor, just something to test if this LED is the cause before doing something potentially damaging .Leave a comment:
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