Re: LG 50PV250 Y Buffer meltdown
Thanks anyway. Do you reckon I need to change the Y Sus board too, to make sure the new buffers don't get fried?
mangozac
Member
Last Activity: 07-14-2019, 05:45 PM
Joined: 02-11-2013
Location: QLD
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Re: LG 50PV250 Y Buffer meltdown
Cheers mate, let me know what you find!...Leave a comment:
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LG 50PV250 Y Buffer meltdown
We were watching TV the other night and *bang* (as in made an actual noise), no more picture. Sound was still working but the ominous smell of vaporised semiconductor hung in the air!
Popped the back off and sure enough the top Y Buffer ICs had a big hole in it. I turned power back on and could see one of the buffers on the bottom half starting to glow too. So I removed both buffer boards and tested the Y-sus voltages Vy and Vsc, both of which were in spec at 150 and -190V (Vsc is confusing as measuring with the polarity indicated on the PCB it actually gives a positive voltage).... -
Re: LG 37LC7D-AB again - Backlight problems
Tentative update: it seems to be working again. I hate intermittent issues!
Since the CFL test was giving positive results I decided to rule out any problems with the MICOM signals and backlight itself and hooked the PSU board up to the backlight on the TV with all of the power supply enable link wires left in place. The backlight came on and stayed on.
OK, maybe the fault is with the MICOM->PSU connections? I pulled off my link wires and connected the board correctly and the TV was all working fine....Leave a comment:
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Re: Possible Purchase: LG 37LC7D
Between [URL="https://www.badcaps.net/forum/showthread.php?t=31474"]this[/URL] and [URL="https://www.badcaps.net/forum/showthread.php?p=363745#post363745"]this[/URL] I'm becoming fairly intimate with this PSU board!
Backlight inverter is on the main PSU board. If the backlight is coming on then it would suggest the main MICOM IC is running and trying to start the set up. I'd say STBY_5V is ok (which is regulated to 3.3V for the MICOM). Not many caps on STBY_5V that would get much stress anyway.
There...Leave a comment:
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Re: LG 37LC7D-AB again - Backlight problems
Interesting. Although the transformer on this board has an extra winding that seems to provide some feedback to the controller IC, it does also feature these voltage divider caps. The controller IC is an MSC1691A but I can't find any datasheet.
I did notice the error output on the schematic you linked to, and it reminded me of the error pin on one of the connectors on my board here. I measured this pin: it started at 5V and when the bulb was switched off it went to 0V to indicate the error. This would almost certainly indicate...Leave a comment:
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LG 37LC7D-AB again - Backlight problems
After my [URL="https://www.badcaps.net/forum/showthread.php?p=363745#post363745"]latest round of repairs[/URL] to this set she worked well for a couple of weeks and then started exhibiting a new issue of no backlight. I still had sound and shining a torch at the screen showed the panel itself to be working. At first the backlight was intermittent - it wouldn't come on when the TV was switched on, but cycling mains power solved it. That worked a couple of times but then it wouldn't come on at all.
The backlight inverter is part of the PSU board:
The... -
Re: Panasonic TH-42PA60A Self Test Failed
I just had a play around and still no luck. Because the D board is behind the DG and H board assembly it's not possible to play with the connection to the D board while the TV is on (I tried and gave myself a boot accidentally touching a heatsink on the P board directly above).
I did plug about with the cable on both ends but it had no effect and I'm convinced it's not a connection issue. While soldering the individual wires is well within my abilities, it would take a while and I don't think it would help.
...Leave a comment:
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Re: Panasonic TH-42PA60A Self Test Failed
Hey tw005 sorry I missed your posts - I thought I had subscribed to this thread :/
This is actually very interesting timing - the used LG 37" LCD that I've been running ([URL="https://www.badcaps.net/forum/showthread.php?t=30702"]since I fixed the power supply squeal[/URL]) just died again last week - no backlight this time. It was intermittent for a couple of days before failing and I can't find enough information to troubleshoot the complex inverted section of the power supply board. I was just about to start...Leave a comment:
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Re: LG 37LC7D-AB Power supply squeal
Thanks budm! I've said in a previous post that despite being an engineer and designing electronic circuits, tracking down faults in equipment that others have designed is a completely different skill set!
It was the resistor that was 0.68 ohms; the zener diode was very close to 0 ohms. The zener diode isn't even suggested in the ICE3B1565J datasheet so it doesn't surprise me that many mould leave it out. So I guess points go to LG engineers for not cutting that corner?
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Re: LG 37LC7D-AB Power supply squeal
She's fixed!
After taking the effort to get the oscilloscope out yesterday I figured I'd keep probing around and checking out the switching signals. This revealed some very anaemic looking pulses on the cold side of the STBY5V transformer. It just didn't look right and there was a lot of ripple on the 5V.
Everything on the cold side checked out ok so I decided the problem lay on the hot side. Resistors all measured OK so I moved on to testing the passive semiconductors. That's when I discovered the fault: zener diode...Leave a comment:
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Re: LG 37LC7D-AB Power supply squeal
Sorry I was on auto pilot when I wrote that last reply! You're right that 10V ripple with that small a load is extremely excessive! I decided to re-measure and realised that the true-RMS feature of the meter averages over a long period and the measured voltage ripple gradually decreases to under 1V.
I was still not feeling confident so confirm it further I grabbed an oscilloscope and isolating probe and measured the voltage. This measured a beautiful, flat 320VDC on the DC bus, so everything there is definitely fine.Leave a comment:
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Re: LG 37LC7D-AB Power supply squeal
I've got a Fluke 179 which is true RMS, which reports 10VAC ripple. That sounds pretty acceptable, right?Leave a comment:
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LG 37LC7D-AB Power supply squeal
This 37" LG LCD was my parents' but when it died early in the year they decided to buy a new one. I intended to work on it eventually and was recently forced to look at it after my Panasonic plasma started playing up.
The LCD would not turn on. Apparently they had been watching it when it made a loud bang and died. Upon further inspection I found that the 2.2R resistor supplying the mains DC bus voltage to the Standby 5V regulator had burned out. I couldn't find a short on the MOSFET of the switching regulator so figured I'd just try replacing the resistor. I did so and strangely... -
Re: Panasonic TH-42PA60A Self Test Failed
I thought maybe some funny business too, but the bid history shows 3 bidders so I would think it maybe less likely.
There's one on Gumtree on the South side of Brisbane (the guy wants 60 bucks), but like you say, where do you draw the line. It's an old, analogue, standard def TV and while it does have some sentimental value, I'm not one to waste money due to sentimentality (not to brag, but I have no cash issues preventing me from buying a new TV). Once the replacement part of the other LG LCD I'm fixing comes in and I see...Leave a comment:
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Re: Panasonic TH-42PA60A Self Test Failed
What the hell that ebay auction is suddenly rocketing up in price! It's at $20 already! Might have to move on from that one!Leave a comment:
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Re: Panasonic TH-42PA60A Self Test Failed
No, it would fit into the tray of a ute at least - I drive a 2-seat sports car. I measured and the 42" display won't fit into the boot and definitely not the passenger seat. There's no space behind the seats either.
Might have to talk the girlfriend into a day down to Brisbane and put it on the back seat of her Focus
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Re: Panasonic TH-42PA60A Self Test Failed
Brisbane is an hour away but the hassle is that I can't fit big TVs in my car! I'll find out what suburb it's in and give it some thought - certainly if I can pick it up for a dollar it might be worth picking up...Leave a comment:
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Re: Panasonic TH-42PA60A Self Test Failed
TVs are a little more expensive here, but a similar sized Panasonic is around the $1k mark.
I just had another look at the image and the red pixels seem to be getting worse. They show up on any transition from a lighter pixel containing red to a darker pixel in the scan direction (left to right). Even the OSD menus, etc. have it. But the internal test patterns are fine.
The fault is somewhere between the DG and D boards and without the ability to swap out test boards all I'm going to be doing is throwing money...Leave a comment:
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Re: Panasonic TH-42PA60A Self Test Failed
Right after considering the issue I think that there is enough reason to try replacing the D board. At first I was concerned because the repair manual lists the D board part number as TZTNP01BMTB, which when Googled is nonexistant. But that's not the part number on the board! The actual PCB number is TNPA3932.
So TNPA3932 boards are fairly readily available. I assume that the TZTNP01BMTB refers to the TNPA3932 that has been programmed specifically for this 42" panel, which can be problematic if I just grab any TNPA3932...Leave a comment:
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