Help with HP-67

[twoweims]

I recently acquired a non-working HP-67.
It appears that there is a short circuit between Vbsw and ground.
When I power it up from the battery terminals with an external power supply my power supply voltage just collapses. The low battery LED blinks momentarily as the voltage drops, which I would expect.

I have isolated the card reader and the logic board and tried to power the keyboard/display board alone and the fault persists.

Vbsw does not seem to do much on this board other than provide Vcc to the cathode driver and the low battery LED. I may be missing something because I don't have a good schematic. I am suspecting a problem with the cathode driver.

Is there a service manual for this calculator. I have the MOHPC Thumb drive and I don't see one on there.

If anyone has worked through this particular problem before, I would appreciate any advice.

Thanks!