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Macintosh Portable M5126 Weird Problem


New member
Hey friends, one of my customer brought me Macintosh Portable for recapping few weeks ago. I did ultrasonic cleaning, alcohol bath, replaced all the caps also checked all the paths under the microscope and nothing were corroded then I tested with PDU (top 2 pins +, bottom 2 pins -) with 6.4V and 1.5Amp, hit the keyboard and it didn't turn on.

Since there is no schematics for M5126 model, I decided to check major power components and traced the important voltage lines and everything was okay. I decided to replace one of the capacitors next to the keyboard socket and run my hot air station for a while near the PMGR (U15H) chip. While the board is hot I hit the keys and it turned on with code 00000014, motherboard cool downed to room temp, and tried to turn it on again but no luck. I decided to apply little bit flux around PIN '1-15' area on PMGR and heated with hot air for few seconds and it turned on. Does PMGR failure common problem on this particular machine?

I'm not super familiar with these machines and decided to share here if any case you might have some ideas. I really want to help my customer. Thank you.


Well-known member
I used to hold down the reset and interrupt buttons (left side of the machine) at the same time for a few seconds then press a keyboard button (spacebar) to get the machine to power up. I thought the Portables were never in a truly "powered off" state so that it can listen to the keyboard?


Well-known member
Does PMGR failure common problem on this particular machine?
Very much so, unfortunately. On the backlit portable, power manager chip is the primary point of failure.

There are not really any replacement chips available, and no one has created a replacement yet.

The backlit portable's power manager chip connects to the VIA in basically the same way the original portable does. So that part of the schematic will be very similar.