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Old 08-03-2021, 05:13 PM   #2
StephE
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Join Date: Mar 2019
City & State: Tuebingen BW
My Country: Germany
I'm a: Knowledge Seeker
Posts: 8
Default Re: A1418 820-00431-A Looping LEDs

Hello,
have you done anything else with that board ?

I have (had) the same problem (cycling LEDs 1-3)

First step was checking for obvious visible problems, didn't find any except for an unusally large amount of loose solder balls all over the board on both sides.

After reassembling the iMac the problem stayed the same for a few minutes, then it changed to LED 1+2 on steady and fan starting/running at full speed.

Schematics around U7000/ISL6372 of 820-3588 are similar, so i was able to find a short on PPVCCIO_S0_CPU (--> dead CPU) and/or pin 13/14 of U7000 (CPU_VIDSOUT/VIDALERT_L)

I think i have found/checked all other parts that may short PPVCCIO_S0_CPU, so this board is done for now. Probably killed by a solder ball rolling to the wrong place)

Is there a datasheet for ISL6372 available anywhere ?

PS i have succesfully replaced FDMF6808N/FDMF6708N with FDMF3030 (on 820-3662 etc.)
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