LG 42LV5400-UB doesn't power up, Micom issue

[Yanleb]

Hi all,

This repair is very challenging. I already made my way to the problem. Please read the complete post before commenting. I need the help from good gurus.

The power button on the TV set is working, the same for the power button on the remote control. When activated the power LED changes from red to white and the power supply relay clicks. But no image appears, and no sound is heard.

I already investigated the problem. the Micom chip on the EBR73110104/EBT61520408 main board is the issue. The Micom is IC602 that use the μPD78F0514 (UPD78F0514) microcontroller. Here are its important inputs and outputs:

Pin 6 - POWER_ON/OFF2_1 - good at 3.5v, it enables 3 voltage regulators

Pin 10 - INV_CTL - bad at 3.5v, it makes Q504 pull INV_CTL_18 down that is sent to INV_ON. I forced INV_ON to high by removing R547 that activates Q504. Now I have the backlight working.

Pin 11 - MODEL1_OPT_1 has 2 purposes. Setting Micom options in entry, and activating PANEL_CTL in output. On output it is at 3.5v, which is bad.
Removed R553 so that Q505 stays inactive, allowing Q506 to activate and pull the gate of Q507 to ground, restoring PANEL_VCC. Now the T-CON board receives its 12v.

Pin 14 - POWER_DET - good at 3.7v

Pin 29 - POWER_ON/OFF1 - good at 3.5v, used by IC508 the 1.5v voltage for the DDR memory

Pin 30 - MODEL1_OPT_2 has 2 purposes. Setting Micom options in entry, and activating INSTANT_MODE in output. It goes directly to the main IC IC101 LGE35230(BCM35230KFSBG). I don't know its purpose. It is at 3.5v with power off, and 3.0v with power on. This is suspect for me.

Pin 36 - RL_ON - good at 3.5v.

Pins 41, 42, 44 and 45 are going to two oscillators. Good sine waveform on an oscilloscope.

On page 58 of the service manual (1. Trouble shooting - No power), there's mention of possible problems with the Micom. It is suggested to Re-download the Micom firmware, or to replace the Micom chip.

The problem is the lack of information on how to reload the Micom firmware. I cannot force a complete firmware reload because the USB ports are not powered on at this stage (no 5v).

The Micom has a debug port (P601). But there's no information on that port. It seems that you can also use the RS232 to reload the Micom firmware, but again no information on how to.

I have been able to extract the files from the LG firmware EPK file using epk2extract (you have to compile it from https://github.com/openlgtv/epk2extract). It contains a mico.pak file, which is the firmware of the Micom in Intel Hex format.

What's the best way to flash the Micom using that file? My TL866II-Plus software (XGPro) is able to load it and decode its content, but the UPD78F0514 is not a supported chip. So I cannot use the ICSP port to program it.

There's also an EEPROM chip (IC601). I suppose it used to store settings. Is there something to try with that EEPROM?

Thanks for your help.

[dskall]

Re: LG 42LV5400-UB doesn't power up, Micom issue

Sounds more like you need to reball mainchip.

[neilc6]

Re: LG 42LV5400-UB doesn't power up, Micom issue

LV series has BGA issues. Heat up the processor with a hair dryer before powering up to confirm.

[Yanleb]

Re: LG 42LV5400-UB doesn't power up, Micom issue

You both were right. Heating the main chip made the set come to live. And my suspect Micom pin 30 (INSTANT_MODE) is now a 60Hz -1.2v to 1.2v sine wave. I think this is the only pin talking to the Micom and the main chip.

I can't believe that another dead set is caused by BGA issues. Time to get my stencils and my electronic heating plate out.

Last question. How many of you are doing manual reballing of these chips? Since I don't have a stencil for every one of these chips I use generic ones and cover the unwanted holes using kapton tape. But this is time consuming. Do you have a better solution?

Thanks again.

[diif]

Re: LG 42LV5400-UB doesn't power up, Micom issue

For economic reasons I'd give it a decent reflow not a reball.

[dskall]

Re: LG 42LV5400-UB doesn't power up, Micom issue

You both were right. Heating the main chip made the set come to live. And my suspect Micom pin 30 (INSTANT_MODE) is now a 60Hz -1.2v to 1.2v sine wave. I think this is the only pin talking to the Micom and the main chip.

I can't believe that another dead set is caused by BGA issues. Time to get my stencils and my electronic heating plate out.

Last question. How many of you are doing manual reballing of these chips? Since I don't have a stencil for every one of these chips I use generic ones and cover the unwanted holes using kapton tape. But this is time consuming. Do you have a better solution?

Thanks again.

I just do a generic stencil and the excess balls don't stick and just come off with clean up.