Weird problem in HP 20S

[mfleming]

In doing similar repairs I found that the PCB pads at each twist post are not necessarily tied together on the PCB itself. All the pads are supposed to be ground and the metal plate and twist posts are connected to battery negative. Try closing all the twist posts and see if that might restore operation. Part of the PCB circuitry might be floating with respect to ground or getting a weird path to ground via some other component.