Chosen Solution
I switched my 31" LG 31MU97-B off at the wall power socket and when I switched it on again a few hours later it was dead. So, untouched between switching off and switching on. Dead means absolutely dead – no power light, no sound to indicate it has switched on, no message about powering off in a few seconds to save energy, no sign of a backlight. I have taken it to a PC repair shop and to an electronics company that deals with monitors (but more usually the industrial type) and both say no blown fuses, no bulging capacitors and that the power board is OK. The latter thinks the display panel itself is probably OK. Since there is no power light, which is presumably low voltage, I’m thinking this must mean something is causing the power board to trip or shut down (almost instantly). Is it (almost) inevitably the mainboard or has someone any other suggestions? Would I be right to think the power board is capable of shutting down when feeding into a short or too high a load or demand from the mainboard?
The freight cost was too high to use the Coppell service. In the UK, I bought a new mainboard from: https://www.equinox.co.uk and monitor is working well again. Maybe I should put the old one on eBay to see if someone wants to buy it to see if they can repair it with a new eeprom,
I got my friend monitor LG 31MU97 with the same problem no power and LED light. I just use PIN point test use service manual for LG 31MU97. And i found what CPU stuck in boot loop with error report. So i just updated Firmware in ROM in IC205 (MX25L8006E) it have error checksum before. It is 1 Megabyte rom. And after update everything works again. I did it with two my friend monitors. It is common problem how i see.
I had this issue and came across this blog that helped fix it with a multimeter and an hour of my time. https://integer13.wordpress.com/2018/04/… Hope this will help others too.
I had the same issue. 31MU97B Monitor died when the UPS was turned off while it was powered on. No lights would light up, nothing on the display. All the voltages looked good. No parts looked bad. So I bought the eeprom replacement from: http://www.coppelltvrepair.com/p/1483/lg… Swapped this out and I’m up and running again. Your mileage may vary. It seems strange that a read only eeprom chip would die, so I was very skeptical to start with, but this did fix it.
If the power board is OK the power ON light should appear. If you disconnect the harness from power board to mainboard, are the voltages correct? There’s a polyfuse in series with the mains input, it could have gone entirely.
This problem is caused by bad software in an EEPROM chip on the mainboard (IC205) and can be repaired easily. If you flash an image of this software on this chip, your monitor will come back to life again. I did this repair for about 5 times and all attempts were successful. If your LG 31MU97-B monitor is completely dead and you are not living in The Netherlands, please send your mainboard to me. I can fix this issue and send the mainboard back to you. If you live in The Netherlands, you can make an appointment via my website mentioned below. Kind regards, Erwin Aarnoudse Monitorkapot.nl The Netherlands https://www.monitorkapot.nl
I know this is a pretty old post,, butI want to add my $.02. I had 2 of these LG 31MU97-B’s sitting around for months from owners who hoped I could fix these. Both users gave up quickly, not wanting to spend more money on a problematic monitor. On an off chance that most things are simple I asked LG how to reset the board. Sitting around for months didn’t do it apparently. LG got back to me instructing me to hold the power button in for 30 seconds unplugged. Naw too easy and not logical. These were both dead as dead can be with not response. Boom! both started functioning perfectly again. What?? I’m still baffled.
I have reset mine with guide with https://integer13.wordpress.com/2018/04/… for awhile then all went back again after power out in my home area. :( now trick with Amp meter does not work :(. I have purchased replacement IC205 ROM from ebay but I do not have tools to do the board repair :( My question is What do I need to do the replacement IC succesfully? what tools do I need?
My 34UC87C led me here. though it’s a different monitor the jumping worked here’s what I did. I jumped pins 8 and 6 without luck. Then I wondered how the fix works. If the rom is on a loop maybe screwing with the clock causes an error or jump elsewhere. So I rapidly shorted 8 and 6 a bunch of times. It eventually worked. pin 8 is vcc so safer than that post about an ammeter.
