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@piernov, I've seen this article, but it hasn't changed anything in my situation, or maybe I dont understand something? Actually my I2C_BKLT_SCL and I2C_BKLT_SDA are 5V, they have continuity from J8300 to U7701. I have already replaced connector just in case. I have tested 3 different displays...

Yes, I have 51,2V present on pin 1 of J8300 and even on LCD LVDS connector side. All resistors around U7701 are measuring OK except two - R7723/4 by schematic should be 10,2 ohm, but on my two (and one donor) boards they are 0,005 ohm. Anyway, they are not related to LCD but keyboard backlight...

So I got two A1398 2015" with 820-00138 boards from different customers, but with exactly same issue - no backlight (image is present). One of them is untouched, the other one has been worked on, but the other technician couldn't find the solution for backlight and gave up - he replaced LVDS...

Yes, the same behaviour when I run internet recovery. I have used clean ME BIOS from you, so I’m sure it was ok.

Maybe it's kind of noob question, but I've never had such case. So mentioned 820-00165 doesn't want to format its internal SSD. Actually it can't unmount drive in order to format it. I have tried different drives and different installers - the same result. If I connect SSD with installed system...

Ok, Thank you!

@2informaticos, I have replaced Q8110 and it seems problem is solved, I'll be testing this iMac for few days to be sure. Another question: is there any replacement mosfet which I can use there instead Q8110? I'm trying to find something on my supplier website, but I can't find anything matching...

It's already third time this computer returns to me with the same issue. It's iMac 27" A1312 with 820-2828 motherboard. Customer uses it for video editing. When he leaves his summer house where this computer is located, after few days computer won't power on. He has to disconnect power cord few...

Of course I have replaced it 😉

Bullseye! I took off J5250 and PP3V42_G3H was completely eaten away. Now computer works fine. There was no ign of corrosion in this area... Anyway, thank you very much for your help!

Sorry, I made a mistake.. The SMC_RESET_L is 3,41V. SMC_MANUAL_RST_L is 2,8V. U5110 pin voltages: 1 - 3,43V 3 - 3,44V 4 - 2,8V 5 - 3,41V 6 - 3,42V 7 - 3,44V 8 - 3,29V R5127 has 0ohm resistance and has continuity to U5110. I have checked all resistors around U5110, they are ok.

I have cleaned that area, replaced U5110. Still the same. After plugging battery SMC_RESET_L is 2,8V. This time when I plugged charger there was a chime but no image or backlight on the screen. I have measured SMC_LID: when lid is opened voltage is stable 2,6V, when cloesd it' jumping between...

I'm working on 820-3476 which came for no power. It had some slight corrosion on JTAG, around R7202, U7600, some on C3201 area and really small stain on U6100. I have removed JTAG, cleaned eveything, replaced damaged resistors, caps, resoldered chips (U6100 too). Computer turns on, works on...

Customer brought in A1278 which was not loading system. I have noticed, that computer had Fusion Drive configured with SSD and HDD in optical drive bay. I took out both, put new SSD and cable, installed new Catalina which went smooth, but in the end computer started restarting. It was loading OS...

Unfortunatelly customer couldn't wait longer as he had to flight back to US. Thankfully, he lives in NY, so I advised him to get to Rossmann repair shop. I gave him our visit card and contact, he will give it to you while leaving computer in Rossmann repair shop. If you will need some additional...

I have already tried another BIOS which I can confirm is good (btw. You shared it with me in another thread). I will try new U7100 and inspect board again for corrosion, maybe I have missed something…

Ok, so if missing voltages are related to iGPU and every other voltage is present, it means that CPU doesn’t turn on anyway, right? PLT_RST_L is 0V, so board is in reset mode. I have no idea what else could keep board in that state..

The only votlages I'm missing from the listed in schematic are PPVCCGT_S0G and PPVCCCPU_S0G. Sadly I just hav noticed, that PPVCCGT_S0G is reading 1,6ohm and PPVCCGT_S0G is 3ohm... So my guess is CPU is dead.

I do, voltage on L7370 is 1,049V

I'm sorry, I was writing this post late at night and forgot about some voltages, so here are the missing ones: PP1V8_S0 - 1,8V PP1V8_S3 - 1,8V PP5V_S0 - 5,10V PP3V3_S0 - 3,3V PP3V3_G3H - 3,41V L7210/20 - 0V U8210 voltages by pins: 1/2 - 3,3V 3 - 3,27V 4 - 5,1V 5 - 3,12V 6/7 - 5,1V 8/9 - 5,10V...