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Old 03-10-2019, 09:46 AM   #61
legonch
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Default Re: lg 60pz550 black screen, no power, etc

bump
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Old 03-11-2019, 11:50 AM   #62
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Default Re: lg 60pz550 black screen, no power, etc

any help? kinda stuck here
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Old 03-12-2019, 10:39 PM   #63
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Default Re: lg 60pz550 black screen, no power, etc

Any help here?
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Old 03-13-2019, 09:36 AM   #64
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Default Re: lg 60pz550 black screen, no power, etc

I never instructed you to buy a different power board. You may have just wasted money on a board without needing to.

I need you to be specific for me. Telling me voltages without telling me what voltage you are measuring is very vague.

I think you have 5V and VA? Is this correct? If you are missing VS, we need to focus on that.

5V = ?
VA = ?
VS = ?

Please re-measure voltages. The voltages missing on both board is concerning. You may have two bad boards, or may not be testing properly.

Voltages 5V, VA, VS and are all measured with respect to TV chassis ground (or the labeled GND pins at the white connectors.

Also, measure the voltage across the legs of the large capacitors in the middle of the board. VERY HIGH VOLTAGE - DO NOT LET PROBE TIPS SLIP.

Re-check EVERY heatsink-mounted part for shorts. Diodes indicated by D will likely have pins 1-3 connected so we are looking for shorts between pins 1-2 or 2-3 (1-3 is ok)
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Old 03-14-2019, 09:32 AM   #65
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Default Re: lg 60pz550 black screen, no power, etc

Quote:
Originally Posted by Unspun01 View Post
I never instructed you to buy a different power board. You may have just wasted money on a board without needing to.

I need you to be specific for me. Telling me voltages without telling me what voltage you are measuring is very vague.

I think you have 5V and VA? Is this correct? If you are missing VS, we need to focus on that.

5V = ?
VA = ?
VS = ?

Please re-measure voltages. The voltages missing on both board is concerning. You may have two bad boards, or may not be testing properly.

Voltages 5V, VA, VS and are all measured with respect to TV chassis ground (or the labeled GND pins at the white connectors.

Also, measure the voltage across the legs of the large capacitors in the middle of the board. VERY HIGH VOLTAGE - DO NOT LET PROBE TIPS SLIP.

Re-check EVERY heatsink-mounted part for shorts. Diodes indicated by D will likely have pins 1-3 connected so we are looking for shorts between pins 1-2 or 2-3 (1-3 is ok)
The voltages at 5v, VA, and VS are the exact same as in my previous posts. the 5v goes to 2.8-3.5 volts upon powering up, then drops to zero within two seconds. VA and VS have no voltages. And yes Im still testing to chassis ground. Im measuring these on the power board, on both sus connectors. Ive checked and rechecked the diodes, and can not find a short.

Reading more about this on the internet, could this issue be the main board? I have used the test outlined where you disconnect the flat cable on they main board, and use a jumper to attempt to get a test pattern. I do not get a test pattern on the screen. Reading further, this tv seems to be plagued by issues with the chip on the main board needing to be reflowed. What are your thoughts on this?
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Old 03-14-2019, 11:01 AM   #66
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Default Re: lg 60pz550 black screen, no power, etc

Please re-read my reply. I am asking you to test the components on the power supply.

We already know that you do not have shorts on the YSUS and ZSUS boards. We also know that the poor soldering on your YSUS and ZSUS boards has been fixed.

You did not answer my question about voltage across the large high voltage capacitors.

In previous posts, you said that you have voltage at VA? You stated you have no voltage at VS? Now you do not have either voltage present?

In your first post, you said you have video signal. This means that your YSUS was priming the panel, and therefore you must have had 5V, and VA and VS originally.

Why would we suspect mainboard? You attempted repairs on YSUS and ZSUS and after that repair your problems got worse. Your soldering of YSUS and ZSUS may have damaged the power supply when turned on because we no longer have VA or VS.

Let us leave mainboard out of this discussion for the moment.

I suspect your power supply is damaged. We need you to test the POWER BOARD for shorts and upload clear photos of the top and bottom of the boards with highlighting of any shorts you locate.

We need VA and VS, these should appear when you turn on the TV.

Do you have standby light? what color when off, Red? what color when on, blue? is there relay click?
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Old 03-14-2019, 09:53 PM   #67
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Default Re: lg 60pz550 black screen, no power, etc

You did not answer my question about voltage across the large high voltage capacitors.

The black capacitors in the middle of the power board, all read 2-3 volts across the pins while the tv is powered on. I tried the new power board, and the old power board. Same results on the capacitors, 2-3 volts is all.

In previous posts, you said that you have voltage at VA? You stated you have no voltage at VS? Now you do not have either voltage present?

I initially get a rise in the 5v when power on to 2.8-3.1 volts. Then voltage drops to zero

In your first post, you said you have video signal. This means that your YSUS was priming the panel, and therefore you must have had 5V, and VA and VS originally.

I do believe i saw some snow on the lower quarter of the tv initially. very lightly though, almost undetectable.


Do you have standby light? what color when off, Red? what color when on, blue? is there relay click?

I do have a red constant standby light when the tv is plugged in, and in the off mode. When I push the power button on the remote, I hear the relay, and the red light goes out. No light on until power off, then the return of the red light.
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Old 03-15-2019, 08:43 AM   #68
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Default Re: lg 60pz550 black screen, no power, etc

Quote:
Originally Posted by legonch View Post
The black capacitors in the middle of the power board, all read 2-3 volts across the pins while the tv is powered on. I tried the new power board, and the old power board. Same results on the capacitors, 2-3 volts is all.
I do not think you are measuring voltages correctly.

There is no way your TV would display any signs of life or relay activity if you only measure 2-3 volts across those large capacitors.

In standby, I would expect to measure rectified AC voltage of 120V * 1.414 = 169V. When power supply turns on, I expect power factor correction circuit to boost voltage to 350V or more. Please connect voltage probes (in DC mode) across both legs of the capacitor. Do not use TV chassis as a ground reference for this measurement. What do you measure OFF and ON?


Quote:
Originally Posted by legonch View Post
I do believe i saw some snow on the lower quarter of the tv initially. very lightly though, almost undetectable.
If you saw a very faint and almost detectable snowy image then that was a good sign and meant that your TV was turning on and the panel was priming. Priming with no video (slightly illuminated panel in dark room) however could suggest bad mainboard (common on this TV) but right now you are saying the panel does not even prime, even dimly in a dark room...


Quote:
Originally Posted by legonch View Post
I initially get a rise in the 5v when power on to 2.8-3.1 volts. Then voltage drops to zero.
Sounds like protection is operating. This is concerning since you say this happens with both the original power board and the new board. Please confirm you have all wires and connections connected EXCEPT Power board to YSUS and Power board to ZSUS. Re-test VA and VS with reference to TV chassis at time of power on.
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Old 03-15-2019, 11:04 AM   #69
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Default Re: lg 60pz550 black screen, no power, etc

Okay, first off, I apologize for driving you nuts.

Secondly, im and idiot. Volt meter was in ac mode......yeah, head slap!!

So,

5v has 5 volts
VA has 54.7
VS 201.6

These read the same on both sus connectors top left and top right

Across the capacitors, 390 volts.
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Old 03-15-2019, 11:08 AM   #70
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Default Re: lg 60pz550 black screen, no power, etc

Those voltages are GOOD. As I suspected, your new power supply is GOOD and you did not need to buy it.

Your old power supply is probably also good.

I will re-iterate my point that your issue likely comes from the repair you attempted on the YSUS and ZSUS boards when you re-soldered the large coils.

I think since you do not have panel priming, your damage is in YSUS board, and even if you did not measure any shorted parts, you may have damaged gate drive resistors, or gate drive ICs... These are small 8-pin SOIC chips on underside of board probably labeled with digits 7371 clearly visible.

We should focus efforts on YSUS board
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Old 03-15-2019, 11:16 AM   #71
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Default Re: lg 60pz550 black screen, no power, etc

I hear both sus boards humming when powered up. Guess thats good. So do I test now for continuity on certain parts?
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Old 03-15-2019, 12:17 PM   #72
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Default Re: lg 60pz550 black screen, no power, etc

Quote:
Originally Posted by legonch View Post
I hear both sus boards humming when powered up. Guess thats good. So do I test now for continuity on certain parts?
Wait! Why didn't you mention this before? If you have humming, then this is good. You never mentioned this before.

Does the panel glow even in the faintest little bit in a completely dark room?

If you turn the TV on, and the panel goes from completely dead/dark to a soft glow in a completely dark room, please tell me immediately.

If this has been happening this whole time, then we have wasted a ton of time troubleshooting all of these "power problems" that don't actually exist because of the measurements.

If your panel "primes", then your issue may be the main board.

If your panel "primes", then turn the TV off, blast the large heatsink on the mainboard with a hot air dryer for 3 or 4 minutes on high, and try turning the TV on again.

Report back.
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Old 03-15-2019, 01:43 PM   #73
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Default Re: lg 60pz550 black screen, no power, etc

I tried that last night. really dark in the house. really couldnt see any screen change with the power on. Screen seems to stay the same, power on or off. I can try tonight in total darkness

I'll blast the heatsink in the mean time.
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Old 03-15-2019, 03:24 PM   #74
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Default Re: lg 60pz550 black screen, no power, etc

found a service manual schematic. going through the flow chart, tells me to check L412. Downloaded a pic of the board, and I cant find it anywhere, can find L411, no 412. Any ideas on location?
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Old 03-15-2019, 05:31 PM   #75
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Default Re: lg 60pz550 black screen, no power, etc

found it, under the heatsink. Nice.

followed the schematic, all the items it said to check, checked out with proper voltages, etc. Schematic says replace the chip.

Ill get out my heat gun, and warm it up slow, and on low. hopefully that fixes this.
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Old 03-16-2019, 09:55 AM   #76
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Default Re: lg 60pz550 black screen, no power, etc

Okay, did the heat gun over the chip on low for 45 seconds. Just to the point I stated smelling something.

Waited 30 minutes, reinstalled the board, and tv is still the same.

I did put the usb wireless internet into a port. blue light came on, normal.

Blacked out the living room, turned the tv on, and do not see any light on the screen.

The red light on the front of tv lights up every time i hit a button on the remote.

Am I overlooking something really simple here? Im stumped.
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Old 03-16-2019, 01:01 PM   #77
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Default Re: lg 60pz550 black screen, no power, etc

Further testing continues. I removed the upper buffer board on the left side of the ysus board. TV remained the same. Reinstalled this board.

Middle heat resistor on the lower buffer board has been getting super hot. Removed the lower buffer board. TV now will run a test pattern type on the upper part of the screen. Attached are the pics of the test pattern.

The two chips under the middle heat sink have heat damage on the back side of the board. Im suspect this is the issue. Recommend just replacing board? Or try and just replace the chips? If just the chips, can you tell me how to diagnose via volt meter?
Attached Images
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Old 03-18-2019, 10:04 AM   #78
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Default Re: lg 60pz550 black screen, no power, etc

legonch:

You are our eyes and ears on your TV so I'm glad you noticed the burn marks on lower buffer board. Definitely sounds faulty.

With lower buffer board removed, and since an image on screen - you have a functioning YSUS board (as we suspected since your fuses were good and no shorted parts)

Regarding the buffer board:

Replacing the individual chips on a buffer board is difficult, requiring delicate and precise work.

After seeing your soldering on the YSUS and ZSUS coils, I do not feel you have the tools or level of skill required to perform buffer board repair so I think you would find it easier and be successful with complete lower buffer board replacement.

Your photos tell me you still have mal-discharge issues that suggest ZSUS problems so we may have to come back to that board. However, try replacing the lower buffer board and then we will see what can be done for the ZSUS board.

Did you ever adjust voltage potentiometers on the power supply by accident?
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Old 03-18-2019, 12:58 PM   #79
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Default Re: lg 60pz550 black screen, no power, etc

Thanks for the reply.

I didnt adjust anything. I wouldnt know where to adjust any voltages.

I ordered a lower buffer board. I agree the screen still seems like there is an issue somewhere, all the pixels arent lit up. They seem to move around if that makes any sense. Like some coming on some shutting off.

I will check in when the board gets here. Thank you again for all your help so far!
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