Re: Hisense LTDN55K321 Purple backlight?
So indeed the back light had turned blue/purple. It seems that there's no real thermal junction between the LED boards and the back panel other than periodic screws to hold them in place. Something I'll remedy if I replace the LEDs.
While the swap out would normally be a cut and dry affair during disassembly I found that there was a strip of adhesive connecting a small part of the front bezel to the LCD panel itself. Had it been all around I'd have been fine as I'd know to expect it but it wasn't and I didn't.
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Daveatfernie
Senior Member
Last Activity: 01-04-2020, 01:04 PM
Joined: 11-14-2013
Location: Middlesbrough
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Hisense LTDN55K321 Purple backlight?
Hi Everyone,
Hot on the repair of my plasma I found a 55" 4K LED backlit hisense tv for £40 on facebook that would be great for a garage TV if I can get it working correctly. The listing said it had a purple tint (and it does indeed).
When I've powered it up and looked through the vents in the rear the backlight can indeed be seen to be purple rather than the usual crisp white I'm used to seeing. Is this a thing? Can all the LEDs change colour like that? I use high power LEDs where I work and am used to seeing a few nm drift in colour when they get hot but to go from... -
Re: LG 50PX990 Plasma Powering itself off
Seemingly sorted. Wish all repairs were as straight forward as this.
I've attached a couple of photos in case people don't know what they're looking for with a dry joint, cold joint, stressed joint.
These pins were the main culprits for me although I reflowed the whole set of pins on the board.
Thanks again for the help
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Re: LG 50PX990 Plasma Powering itself off
Only just managed to do some investigation today. Surely enough on the back of the PSU board there's a few cold joints around the transformers. I'll refit the board tonight and test it. If this ends up being the culprit I'll post pics so others can see where the problem was. Definitely cracking around the transformer pin so likely as not to cause a power loss under thermal stress.
I was quite surprised to see how the board has discoloured around the transformer. Do the boards discolour a lot on their own or are the components really...Leave a comment:
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Re: LG 50PX990 Plasma Powering itself off
Apologies, Is it the board with the FPGA I'd replace or the board with the XD processing chip on it (the BGA with the two memory IC's next to it)
One appears to be the control board (50R1X_CTRL) the other (the one with the FPGA) is I assume is for OSD and test signal generation?Leave a comment:
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Re: LG 50PX990 Plasma Powering itself off
Thanks for the replies,
I'll check the back of the PSU board. I could look to get the processor reballed as we have pretty good BGA reflow capability at work. Certainly a couple of things I can check to be going on with.
It may well be though that if I find nothing wrong with the PSU board I'll see if there are any second user boards I can swap in. I'll have a chat to the lads and see if we have any suitable stencils.
Thanks againLeave a comment:
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Re: LG 50PX990 Plasma Powering itself off
I managed to find the supply voltages sticker in the chassis so I'll have a look tonight to see what they look like compared to the PSU output.
There seems to be a wealth of spare boards if required on e-bay but I'd prefer to not have the board in a skip.Leave a comment:
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LG 50PX990 Plasma Powering itself off
Good morning
I have an intermittent 50 inch PX990 plasma TV which I think has electronics based on the 50PK990.
Recently it's started turning itself off after being on for 10-15 minutes and gets to the point where it will only stay on for a few minutes before turning off.
When it turns off and you try to turn it on you can hear the relays clicking in but it clicks off immediately. Leaving it for a few minutes (perhaps to cool or discharge) allows the TV to be powered up for a little while.
I've repaired quite a few LCDs previously but the back... -
Tascam CD-200i
Hi,
I've been given a faulty TASCAM CD-200i from a friend.
It is a CD player with an ipod dock and at £400 i thought worth a look at to fix.
The fault with the device is that the screen illuminates and the CD drive spins up and remains spinning, but that's as far as it gets.
No data on the display.
Does anyone have any pointers as to the standard voltages found inside these devices so I can have a probe around?
Many thanks in advance.
David -
Re: LG 39LN575V Backlight down
Let me tell you a story about an inadvertent win.....
So needless to say I watched the vid (thanks very much for that they were nicely informative). I imagined that would be the problem as the PSU visibly looked OK. As I have a reflow station and a hot air gun at work I planned to repopulate the led with a spare.
Stripped the to down and got to the backlight. I disassembled each strip and powered them to find the faulty led(s) and all of them worked ok. :/
I reassembled the tv and realised that I'd forgotten to re plug the edge connector....Leave a comment:
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Re: LG 39LN575V Backlight down
Superb stuff thanks, looks like the psu and leds are not a bad price.
Very pleased with the set. I'll update with the repair.Leave a comment:
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LG 39LN575V Backlight down
Hi All,
I've just picked up this TV for £20 through facebook. The guy I got it from had said that the screen had just gone off. When I got it home I couldn't hear any inductive pop when I plugged it in so changed the fuse and it powered up.
When I hit the power button the tv comes on but there is no backlight.
I've never looked at an LED backlight before. Is it the same as a CCFL? Look for a powering 24V (or other voltage to watch for). Are they likely to fail as a set or a single led and finally if they've given up the ghost are they replaceable?
I only ask as I have... -
Re: Polaroid P40LCD12
That's what I was thinking with the LED not being illuminated.
Ill try the psu shorting again, if there's no joy I'll start by getting a new psu.
If I can get the psu to fire up I'll get a mainboard.
Thanks again for all your help.Leave a comment:
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Re: Polaroid P40LCD12
Tried forcing the psu in with the mainboard removed using a 470 ohm resistor but this was unable to start it either. (Connecting between 5v and power on input).
Still nothing other than 3.3 and 5v. The mainboard seems to be not trying to power the psu up.
The sw-switch input varies (sits at 5 when the mainboard is unplugged but raises to 7 with it connected). I'm unsure what this does and haven't traced it through the schematic yet.
I was thinking of trying to bastardise one of my other tv psus to power the board to see if it...Leave a comment:
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Re: Polaroid P40LCD12
I've double checked all I can (electrolytics and such) but to no avail.
I'm surprised if it is the PSU board that the ST_BY would not be at 5V or similar though trying to get the power supply to fire up.
I'll buy a PSU board and then a logic board.
Hoping that the screen itself is in good nick after this
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Re: Polaroid P40LCD12
I've tried to force the Sower supply to come up without any other board plugged in by connecting the ST_BY to 5V with a 10K.
I'm going to recheck the PSU board to see if I can see anything.Leave a comment:
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Re: Polaroid P40LCD12
Yeah, Nothing at all. With the any of the cables removed or not the PSU Never tries to power anything other than 5V and 3.3V.
I'm looking to buy a PSU and a mainboard but at the moment don't know which I'll need. Without testing that the PSU comes u pon it's own I can't tell.
Thanks
DavidLeave a comment:
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Re: Polaroid P40LCD12
Thanks I've cross posted onto this one as the other post was not resolved. That TV had a different fault as far as I can see as the PSU was powering up on it's own whereas mine stays in the standby mode. These are the schematics I was able to find also.Leave a comment:
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Re: Polaroid P40LCD12 SMPS Voltages Help please
I have the same TV with a fault. No LED blinking on mine.
(was steered here by another helper)
My PSU when unplugged from the inverter and mainboard only generates 5V on pin 4 and 14 then 3.3V present on pins 15 and 16. None of the other voltages are present (I assume as the mainboard isn't plugged in to ask them to come up)
It sounds as though yours has powered up without the request from the mainboard?Leave a comment:
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Re: Polaroid P40LCD12
On the output connector I can see:
SW_Switch output 7.425V
5VSTBY 4.8V
3.3VSTBY 3.3V
and no other voltages on the board conector.
As far as inputs I've found the ST_BY which I assume is the power supply on connector.
Everything else is an output from the PSU rather than an input from what I can see.
(Other than BL_ON, DIM, and A/D DIM).
Do you think I can 470 Ohm link ST_BY to 3.3V or 5 without the mainboard connected to see if it powers the board on its own?
Thanks again...Leave a comment:
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