HP-42S battery drain

[Marcovecchio]

I have been trying to investigate the issue in more depth, and I confirmed that it's indeed the processor drawing the current: I located the processor GND pins, and carefully cut the PCB trace. The current measures 0mA. I reconnected the trace and immediately got the old 17mA.

However, I noticed another very interesting thing: current draw goes to normal (less than 1mA) in some screens of the self test routine! ROM, ROM OK, DISP, BEEP and a few others measure very low current, while the others show the battery draining issue. That didn't ever happen during normal use. Even turned off, it draws 17mA.

Probably the self test disables the defective processor circuitry somehow. My last test will be to navigate thru the menus and options, changing flags and options, in an attempt to find any setting that may lead to the same behavior I saw during self test.

Another possibility: the processor certainly has a switching transistor to drive the IR led. Is there an easy way to test if the IR circuitry is ok, if I don't have an IR printer? This transistor might be damaged, and leaking current. Does that make sense?

Eduardo

Eduardo