820-3115 low ppbus_g3h, no obvious short (until you look carefully)... green light ok


Hi guys,

Having UC this one (was pretty messed up) I replaced U6990 and got a green light (at least thats how I remember it and in a hurry noted on paper - since this board was written off for a couple of months) but the system is still dead.

Measuring around I discovered that my ppbus_g3h was 1,2V, measured around a bit more and I decided to replace the isl6259 which brought the ppbus_g3h to 4,12V (I should have kept measuring as you ll read further down).

L6995 measures 0,070 in diode mode but when removed the right side (pin1) measures 0,58x. I thought maybe there is a short somewhere and I applied 1V as per Louis (http://advancedreworks.com/forum/arc...hp/t-1476.html) on the 0,070 side (brain activity has considerably slowed down by now) but nothing gets really hot and thats expected from a few milliamps draw.

EDIT: as per this thread: "https://www.rossmanngroup.com/boards/forum/board-repair-troubleshooting/1013-mbp-820-2936-with-short-to-ground-on-pp3v42_g3h-and-no-orange-or-green-light" I must inject 3.4V which also makes sense - will do this and come back soon. Please read on...

F7040 diode mode is 0,434.

Finally a few minutes ago I just measured short (diode mode 000) at pin2 of ALL THREE L7510, L7520, L7550 (raised one side from the pad with the soldering iron). Is the CPU fried? Should I inject voltage here?

Should I just name this sucker "donor"?

Thanks for any input guys.

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Staff member
CPU coils show very low value, especially for i7 (001)...

Peel off the black sponge near BIL connector.
Usually bad cap underneath, going to audio area; one of C6400/3/5.