LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

[ngth82]

Hi all -

Pictures are coming in the next post.

I had a customer drop off an LG 42PQ30 TV the other day. He ordered a new power board, new Y-sus and new Y-buffer off of eBay. I currently have the original boards and the "new" ones as well. I downloaded the service manual and training manual for this unit, but I would appreciate some help as well..

All of this debug is going to start with his ORIGINAL boards because the replacements that he bought didn't result in a change in behavior.

Vitals:
Model 42PQ30
Panel: PDP42G20034

Board part numbers
PSU board: PS-7411-1-LF Rev:2.1 2009/07/08
Y-sus: EBR61018101
Y-buffer: EBR63394602
Logic Control: EBR63856402
Z-sus: EBR61021001
Main board: "TEMPORARY PCBID" B9M9902-02606 / EBT60686126

Panel sticker Voltages:
5V / VA:60V / VS:194V
N/A / -180 / 135 / N.A / 80 (corresponding to Set Up / -Vy / Vsc / Ve / Vzb)

Training manual:


I swapped all the components back to the original ones that were stock to this TV. When the TV is turned on via remote or initially plugged in, the PSU relays engage, There is a short (~1second) buzzing noise from the Y-sus board then the relays on the PSU click off.

To debug, I start with the power board and main board for a static test. When i disconnect the power cable between the power board and the Y-sus. The power board stays on. The power Led on the front of the TV goes from red (stand by) to blue (on) and blinks 3 times.

I get my initial readings here:

5V rail ==> measures 5.04V
VA rail ==> measures 59.93V
VS rail ==> measures 193.9V

These are spot on compared to the panel sticker. So at least the PSU is good.

I then add only the Y-sus board (again, the original board -- no Y-sus, or anything else connected to Y-sus). Plug it in. The relays click on, then click off. I'm assuming this is the usual protection mode.

I'm going to leave the Y-buffer board disconnected for now. I want to see the PSU, Y-sus, Z-sus and logic work first.

Referring to Page 37 of the training manual, the power distribution:
- Step 1 - AC in. Check.
- Step 2 - stby 5V. Check.
- Step 3 - AC check. Good
- Step 4 - power on remote or button. Check. Red light to blue light.
- Step 5 - Relays turn on. 5V detect. Check.
- Step 6 - 12V (measured 12.4V) and 17 V (measured 15.3V) are generated to the main board.
- Step 7 - 5V shows up at M5V REG.
- Step 8 - on the Y-sus board, the 15V test point is at J269. I measure 17.14V for a solid second until the SMPS turns off. Seems to be good.
- Step 9 - At this point, I plugged in the ribbon cable between the Y-sus and the Control PCB (the small green one in the middle). 15V and 5V are present on the control PCB. Again, this shuts off about 1 second later. At this point, the Y-sus makes a funky buzzing noise. What gives?
- Step 10 - 15V and 5V (actual 17.14V and 4.9V) are passed on to the Z-sus board. Again, 1 second later. Things shut off.
- Step 11 - leads to Step 12 - Vs and Va on.
- Step 12 - Vs and Va are supposed turn on here. I get 0 volts for both rails with my DMM>. My oscilloscope confirms the same thing - no voltage rise on these rails at all.


The VS_ON signal from the main board asserts, then it shuts off. To make sure it's not a problem with the main board, I went back to the original configuration of JUST the main board and SMPS board. VS_ON stays HIGH at 3.3V.


I tried swapping to the replacement SMPS and the Y-sus that was provided to me - but same buzzing noise on the Y-sus occurs when the Control board is plugged in. Interesting. Now, that seems to point to a bad control board, doesn't it?

[ngth82]

Re: LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

Pictures. See attached. Thanks!

[ngth82]

Re: LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

Debug continues.

I'd like to point out that my control PWB looks different from the one shown in the service manual. I'll look for a set of schematics on this one tomorrow.

In any case, I checked the 25MHz oscillator. The result is shown in the attached pic. Instead of 25MHz, it's 227Hz between rising edges.

Also, the non-monotonic nature of it appears to be noise picked up from the Y-sus as it buzzes.

The LED on the control PWB doesn't illuminate either.

IC121 - Device marking AZ1084S-3.3E1 (3.3V fixed output regulator - )

Pin 3 - 5V, present. - measures as 4.7V
Pin 2 - 3.06V measured output
Pin 1 - GND
TAB - 3.06V

The output seems a bit low for a 3.3V fixed output.


IC171 - Device marking EH18A (https://cdn.badcaps-static.com/pdfs/...87732c18fd.pdf) - 1.2V fixed output LDO

Pin 1 - GND
Pin 2 - OUTPUT - 1.172mV
Pin 3 - INPUT - 3.06V
TAB - OUTPUT - 1.172mV

[Andrew F. Ali]

Re: LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

Could that be the Z-sus Bd has a problem and shutting down the TV? Or is it just a bad panel? (rare but possible)

[ngth82]

Re: LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

Hi Andrew -

Thanks for the reply - in the process of debugging the TV, i had the Z-sus disconnected.

I started with "everything" plugged in, then isolated only the main+SMPS, then added the Y-sus, then the logic. Adding or removing the Z-sus didn't make a difference.

I guess it's possible that it's a bad z-sus or a bad panel. The ower of this tv purchased a new SMPS, Y-SUS and Y-Buffer board, but did not purchase a new logic, main, or Z-sus.

-Thomas

[ngth82]

Re: LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

Good morning all -

I ended up ordering a replacement control board off of eBay for $10. The "EBR63856402" board has the same sticker markings for the firmware load. It should be here next week. I'll update this thread once I have it in hand.

[ngth82]

Re: LG 42PQ30 - Y-sus board clicks when logic board is plugged in.

The control board did not fix the issue. I returned the TV to the owner. Unresolved.