HP-97 not Charging

[aj04062]

Hi,
I recently acquired a very nice 97, however it does not run or display connected to the AC adapter. Works fine with a charged battery. I tested charging circuit by running the battery dead then attaching the AC adapter. Still nothing.

Naturally I then checked the charging circuit resistors on the keyboard PCB. These seem to be fine.

The AC adapter is fine as it runs other machines.

I’m have several other machines. To my surprise the everything works as expected by swapping the logic board with another one. In other words, it appears that the logic board seems to be at fault.

I’ve checked the transistors and resistors on the logic board and they seem fine.

Any ideas on where to look next?