I finally had some time to have a look at replacing the CPU. And it worked.
So for me, the fix was replacing IC401 with MP2122AGJ + CPU.
So i can finally vouch for the aliexpress link i posted. The CPU is good....
Pandor
Member
Last Activity: 02-07-2025, 06:31 PM
Joined: 10-09-2016
Location: Bruges
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I have a link up in post [URL="https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-computer-displays/97394-lg-27gl63t-b-completely-dead?p=3219048#post3219048"]85[/URL] for the ali platform. They go for around $20-35. Voveo also posted a taobao link.
I'm curious as to what soldering technique [USER="499229"]voveo[/USER] used.
Unfortunately i can not find a replacement board for the life of me, so this is a last resort. If this doesn't work i'm binning the monitor.I have a link up in post [URL="https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-computer-displays/97394-lg-27gl63t-b-completely-dead?p=3219048#post3219048"]85[/URL]Leave a comment:
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Its finally here. At first glance, it looks fake (comparing the logo), but anyway. Wasn't aware this chip would have a bottom ground plane, so that's going to be a p.i.t.a. i'm not overly confident. I've done bga cpu's, but qfp chips don't tend to just flow in place under hot air... we'll see....Leave a comment:
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So, if I understand correctly. The low resistance on the memory power supply was not the issue? The low resistance measures the same on the new CPU? But replacing the CPU revived the screen? I'm currently waiting on my replacement MST9U35Q1 from aliexpress....Leave a comment:
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I'm afraid my problem is also the cpu. Do you have any resistance measurements with the new cpu?
[USER="462830"]markismus[/USER] this should work: [url]https://a.aliexpress.com/_EuyUHWv[/url]markismusI'm afraid my problem is also the cpu. Do you have any resistance measurements with the new cpu?
[USER="462830"]markismus[/USER] this should work:...Leave a comment:
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The 27gl850 service manual posted on the first page is virtually identical, minus the USB and buzzer stuff. most of the schematic matches the 27GL650 board we have. I've been using it as a reference.
Here's the UART part:...Leave a comment:
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I hooked up my USB to TTL adapter, and no output at all. I could hook up my logic analyzer, but this is getting nowhere... I'm getting fed up with this LG cr*p. I feel like just taking the loss and tossing it....
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markismus...
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its funny how we now have 3 'completely' different dumps of the firmware. The EEPROM content is also completely different.
But upon some investigation, and trying to understand how the CPU/Scalar works, I believe the EEPROM only contains the user settings for the screen (source: [URL="https://support.hp.com/id-en/document/c03523431"]HP Compaq LA2205wg 22-inch Widescreen LCD Monitor[/URL])
I tried searching for the latest firmware, using these techniques: [URL="https://blogger.davidmanouchehri.com/2020/01/how-smart-is-my-monitor-part-1.html"]RFC 3514: How Smart Is...Leave a comment:
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markismus[USER="462830"]markismus[/USER] here are my dumps, from the desoldered chips....Leave a comment:
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I think there are to much devices on the 3.3 line, and my programmer can't handle that. I have a hot air station, so desoldering is not that big of a deal. Judging from other LG monitor model malfunctions and some research, it could be possible that the eeprom actually contains a bootloader/management for the cpu, so that could possibly be the culprit. But i'm speculating.....Leave a comment:
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i have not tested IC402, as that is only for the screen power, and i'm not even getting standby. But i could test it.
i suspect it'll function as it should. I was more focussing on atleast getting the standby led to turn on, and have the board in a standby state. I just tried reading both the eeprom and flash in place with a clip, and for IC201 i get something, but for the IC 202 flash, i get FF. I guess i'll have to desolder....Leave a comment:
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I guess we're in the same boat now. I injected 1.8v and it was only pulling a few mA. In a last attempt I reflowed 401 and now i have 1.8v back. So currently all voltages seem correct, as yours. Still no life. Firmware maybe? I did not replace or check the crystal yet....Leave a comment:
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Are you sure you're getting 5v on pin 6 (SW1), did you doublecheck the input at the coil L408? That is way to high! Should only be 1.8V. I your reading is correct you're sending 5v into the CPU DRAM/IO...
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No life at all? Atleast you're getting all the correct voltages afaict...
This monitor is a tough nut to crack it seems. I was thinking about getting another cpu on alli, but they're like 30€ and no gurantee. Thats a lot to spend on this POC.....Leave a comment:
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markismus posted some great pictures with correct IC labels and datasheets, one page back.Leave a comment:
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Those readings seem to be way off. after replacing 401, i get:
IN=5v
EN1 and EN2=3.3v
SW2=1.16v (close enough)
But SW1 goes straight down to 0.08v. so in my case, something is overloading the SW1 side, making it go into protection mode.
I have a bad fooling the CPU is taking the rail down..
...
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the powerrails actually match up in the service manual. Only IC401 seems to be IC403 in the schematics. This also explains why IC 402 would be low, as that seems to generate the 12v for the panel.
So i seem to be missing 1.8v, or rather it drops out at power up. I'll dig some more on that rail.
I'll just inject 1.8v into that rail and see what gets hot, and the power draw. Something on that rail seems to bring it down as soon as it powers up. Resistance on the unpowered rail seems fine though.
I just hope its not the CPU, as the 1.8v seems to split into VDD_DRAM...Leave a comment:
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I believe that would be the AKX. The ic numbering might be different, but the general power rails seem to match. The AKX is the only dual output, so hence my assumption.
For me the AKX seems to start at 2v output briefly, but goes down to 0.08v on SW1. So it could be going into safe mode/protect. The weird thing is that the SW1 side does not seem to have a short on my board, but the SW2 side has a rather low resistance to ground. If anyone can confirm it should be 2.5v, i might try injecting that after the coil.
[USER="462830"]markismus[/USER] the abcence of...Leave a comment:
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My expected output voltages were based on the LG 27gl850 service manual posted in this thread. I assume the voltages should match... as this model doesn't differ that much.
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