LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

[ngth82]

Good evening everyone -

I searched the forum and found two semi-active threads on the LG 55LV5500-UA.AUSYLJR, but the symptoms do not necessarily match what mine is doing. A few pictures are attached. I appologize for the quality of some of them as i do not have a good light source and it's dark out. I will repost the pictures tomorrow when there is sufficient daylight.

Let me describe my issue:

1. Plug in the TV. The power LED turns white, then red. The LG LED color code is as follows: red = standby, white = on.
2. Push the power button, the power LED turns white, and the relays click on.
3. The backlight is NOT on.
4. No audio or video is seen on the display.

Sounds pretty much the same so far... but stay with me here

I found the schematics and the service manual for the TV online:
Service manual / schematic:

• http://elektrotanya.com/lg_55lv5500-.../download.html
  http://pages.sssnet.com/test/LG_55LW5600_Training.pdf

(Note that the second link is for the 55LW5600, but the power board is the same as the 55LV5500).

The power board (p/n: EAY62169901) caps are fine. Nothing is bulged. The power board generates 3.5V standby, and see a well regulated 12V and 24V to the main board at right, and 56V to the panel LED strings at connectors P202, P203. This is done by shorting pins 9/10/11/12 (STBY_3.5V) to Pin 1 to turn the supplies on when P502 is connected from the main board.

I can force the backlight on as well by jumpering pins 9/10/11/12 to pin 18 (DRV-ON). I'm confident that the backlights are good, and the power board is good as well.


The main board receives 12V and 24V. I checked the voltages across the caps and all of them appear to have the correct voltage per the schematic.

12V appears from the main board ribbon cable at the T-Con. The fuse is intact. I see 12V on both sides and all the regulators on the T-Con appear to have stable power rails as well.

Looking at the schematic (page 55 in the first link), I see that INV_CTL is connected to the MICOM. That signal is driven to 3.5V, which in-turn drives a NPN and sets INV_CTL_18 low (0V). INV_CTL_18 is connected to the power board and is the pin that controls the backlight.

The issue appears to be with the main board, but this is where i'm stuck. Does anyone have any experience in debugging the MICOM IC? It's a proprietary device so i'm not familiar with it.

I can definitely debug the rest, but if someone has some knowledge about the MICOM, or wants to chime in, that would be much appreciated.


Thank you!
-Thomas

[budm]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

The main board may have sense some error so it does not send out the command signals.
What happen if you monitor the PS-ON pin then activate the power switch and see if the PS-ON goes high and stay high or it drops out after a second also may due to error detection.
You can also try disconnecting other boards that are connected to the main board except the power supply board to see if the TV will stay on.

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Hi Budm -

I checked the PS-ON signal (pin 1 of P201 on the power board). The signal is driven high to 3.5V when the TV power button is pressed. This signal does not go low.


I also tried disconnecting the ribbon cables to the TCON, but that does not change the behavior in any noticable way. PS-ON is stable, and the output rails are all still on (12V, 24V).

Speaking of errors, i did check the ERROR_OUT pin (pin 24 to the main board). Its low and does not change state when the TV is off, or on.

-Thomas

[budm]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

OK, I need to download the service and the training manual to find out if ERROR-OUT LO = normal, or HIGH = normal.
Did you read through the manual to find out?

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Heh! Real time collaboration!

The 55LV5500 service manual does not indicate if ERROR is active high or active low.

However, the second link to the LV5600 display uses the same supply board and has some indication that ERROR is active high.

I'm combing through the documentation that i have looking for additional clues.

-Thomas

[budm]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

That is for me for tonight, my internet is really slow right now and it is still downloading the files so I will let it finish downloading while I go to bed.

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Sounds good. I do appreciate the help!

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Sounds good! I do appreciate the help!

[dick_barton]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Looking through the Training Manual I believe that the INV_CTL from the mainboard should be at 3.28V

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Looking through the Training Manual I believe that the INV_CTL from the mainboard should be at 3.28V

I concur with that statement (but with the standard voltage +/- 10%). To clarify:

The schematic shows that the collector of Q504 should be 3.3V when the TV is operating normally. This is in alignment with the backlight check that I described with the power board (connect pin 18 to either 9/10/11/12 which drives it high) with the debug techniques in the training manual.

This goes back to my original statement/question: I see that INV_CTL is driven HIGH (3.5V) from the MICOM when the TV is turned on. This is connected to the NPN Base.

This causes the NPN to turn on, and the voltage at the collector goes down to 0V facing the power board. In turn, INV_CTL_18 to the power board is also 0V. Anyone have any knowledge/insight as to what the signal states/qualifications are required for the MICOM to assert a INV_CTL low (and in turn have the NPN collector be 3.3V)?

[budm]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

The INV_CTL_18 should be LOW (<1V) when TV is in OFF/or standby mode (backlights are off) Q504 (Inverter) is ON, when power switch is activated, Q504 is then turned OFF to allow the Collector Voltage to go HIGH to turn on the backlights inverter circuit.
I did not look at the diagram yet to see if the MICON output is directly drive the Base of Q504 or it driver another Transistor (Inverter) to invert the output of the MICOM signal then that that Transistor drives the Base of Q504.

[budm]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

OK, MICON IC602 pin 10 (P71/KR1) drive the Base of Q504 (Inverter), so when the TV is OFF/STANDBY, MCIOM output is HIGH to keep Q504 ON so the Collector will be <1V.

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

OK, MICON IC602 pin 10 (P71/KR1) drive the Base of Q504, so when the TV is OFF/STANDBY, MCIOM output is HIGH to keep Q504 ON so the Collector will be <1V.

Thanks for double checking the schematic. I concur.

Right now, the MICOM output is HIGH, and the Q504 collector is low (like 10mV). That circuit appears to be doing what its supposed to do in response to the MICON pin 10 being HIGH. ... just need to determine why the microcontroller logic is keeping it high!

I'll take another look when I get home this evening and continue debugging the main board on the TV.

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

It's been a few days since i've looked at the TV. I should have some time to look at it this evening and i'll report back with my findings.

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Hi Guys... here's an update:

I looked at the 55LV5600 service manual and saw there is a Turn On Command Circuit drawing (attached). Since the power board of my 55LV5500 is common to the 55LV5600, i traced the turn on sequencing.. This is what i found:

• Step 1 is good: I have +3.5V_ST at the IC602 (MICOM) and Q502.
• Step 2 is good: Key 1 and Key 2 are both high (3.3V)
• Step 3 is good: RL_ON is asserted by the MICOM and can be traced all the way to the SMPS board.
• Step 4 is good: +12V and +24V are up on the Main Board.
• Step 5 is good: The +12 and +24V monitors are wired-OR'ed together. The output is high. POWER_DET is good.
• Step 6 is good: The switching regulator for +3.3V_NORMAL is good as well.
• Step 7 is good: PANEL_VCC (+12V) is seen on both sides of the T-CON board fuse.
• Step 8 fails. INV_CTL out of IC602 (MICOM) is HIGH. This drives the Q504 base HIGH, and the collector node LOW to INV_ON. INV_ON is DRV_ON on the SMPS board. The TV backlights are still off and no further turn on sequencing is observed.

Other observations:
The service manual states if either P202 or P203 (the connectors for the panel backlights) are disconnected, the backlights should turn on for about 4 seconds then turn off. This doesn't happen. (But i think it's a red herring for me since the DRV_ON signal is not working in the first place!)


I believe the MICOM (IC602) input conditions should be satisfied. So it sounds like i have a busted main board and unfortunately it's the microcontroller with proprietary firmware.

Does anyone have any additional ideas? or if this board is still available for sale? I checked shopjimmy and eBay, but couldn't find an exact match for the LG 55LV5500-UA.AUSYLJR TV model number, or the EAX63333405(0) main board.

Thank you,
Thomas

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Update: I called LG and they referred me to their local distributor -- that was a nice surprise! I have ordered a brand new main board for ~$180. I'll update this thread once i receive it and let you guys know what happens!

Thank you,
Thomas

[artstv1]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Good evening everyone -

I searched the forum and found two semi-active threads on the LG 55LV5500-UA.AUSYLJR, but the symptoms do not necessarily match what mine is doing. A few pictures are attached. I appologize for the quality of some of them as i do not have a good light source and it's dark out. I will repost the pictures tomorrow when there is sufficient daylight.

Let me describe my issue:

1. Plug in the TV. The power LED turns white, then red. The LG LED color code is as follows: red = standby, white = on.
2. Push the power button, the power LED turns white, and the relays click on.
3. The backlight is NOT on.
4. No audio or video is seen on the display.

Sounds pretty much the same so far... but stay with me here

I found the schematics and the service manual for the TV online:
Service manual / schematic:

• http://elektrotanya.com/lg_55lv5500-.../download.html
  http://pages.sssnet.com/test/LG_55LW5600_Training.pdf

(Note that the second link is for the 55LW5600, but the power board is the same as the 55LV5500).

The power board (p/n: EAY62169901) caps are fine. Nothing is bulged. The power board generates 3.5V standby, and see a well regulated 12V and 24V to the main board at right, and 56V to the panel LED strings at connectors P202, P203. This is done by shorting pins 9/10/11/12 (STBY_3.5V) to Pin 1 to turn the supplies on when P502 is connected from the main board.

I can force the backlight on as well by jumpering pins 9/10/11/12 to pin 18 (DRV-ON). I'm confident that the backlights are good, and the power board is good as well.


The main board receives 12V and 24V. I checked the voltages across the caps and all of them appear to have the correct voltage per the schematic.

12V appears from the main board ribbon cable at the T-Con. The fuse is intact. I see 12V on both sides and all the regulators on the T-Con appear to have stable power rails as well.

Looking at the schematic (page 55 in the first link), I see that INV_CTL is connected to the MICOM. That signal is driven to 3.5V, which in-turn drives a NPN and sets INV_CTL_18 low (0V). INV_CTL_18 is connected to the power board and is the pin that controls the backlight.

The issue appears to be with the main board, but this is where i'm stuck. Does anyone have any experience in debugging the MICOM IC? It's a proprietary device so i'm not familiar with it.

I can definitely debug the rest, but if someone has some knowledge about the MICOM, or wants to chime in, that would be much appreciated.


Thank you!
-Thomas

If the red light is on and turns color when turned on that means you have stand by voltage, If the relay clicks it generally means the main is ok, flash rom is working. So that means ether the tcon is bad or bad LEDs. I would say bad LEDs. That is common with LG tvs.

[budm]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

If the red light is on and turns color when turned on that means you have stand by voltage, If the relay clicks it generally means the main is ok, flash rom is working. So that means ether the tcon is bad or bad LEDs. I would say bad LEDs. That is common with LG tvs.

His DRV_ON (BL-ON/INVR-ON) is stuck LOW when TV is turned on so no backlights.

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

If the red light is on and turns color when turned on that means you have stand by voltage, If the relay clicks it generally means the main is ok, flash rom is working. So that means ether the tcon is bad or bad LEDs. I would say bad LEDs. That is common with LG tvs.

Hi artstv1 -
I know the backlights work. I forced them on by "jumpering pins 9/10/11/12 to pin 18 (DRV-ON). I'm confident that the backlights are good, and the power board is good as well." (please see the original post).

This method was detailed out in the service manual that i attached.

Thank you,
Thomas

[ngth82]

Re: LG 55LV5500-UA.AUSYLJR - Does not turn on, no sound, no picture

Sorry: I hit submit too soon:

The problem is currently with the DRV-ON signal is stuck low when i have everything connected for "normal" operation. I posted the power on flow in reply #15, above and where things get stuck.