HP-10BII+ calculator

Self-test mode.

Pressing PMT + ON will enter the self test mode. Using + and - to chose the test gives me the following options:
I 5crEEn
2 kEyboArd
3 ChEck5uM
4 bAttEry
5 VEr5ion
6 CoPyri9ht
7 tE5t 5y5
8 5Iou CLk
Pressing = will run the selected test and at the end of it, press = again to return to the menu.

Some self-test results on my calculator:
Test 5 Version: 7-13-2010 2
Test 3 Checksum: 244.244 (number before is the calculated number, the other is the number put in the flash to compare against and should match, as per TW info)
Test 4 Battery: 2.900 (I need fresh batteries here...)
Test 8 Set I/O Clock: SC-28,500.00 (it allows some adjustment of the clock speed if the serial communications are behaving unreliably, as per TW info)
Test 6 Copyright:  COPr HP 2010 1,752.00 (Size in bytes of the internal calc structure, as per TW info)

 

 

Re-flashing is possible, thanks to the exposed I/O serial interface in the 6-pin  pogo connector.

HP-16C vs HP-15C

Casio fx-61F: Scientific Electric Formula 27 calculator

Solar cells panel able to genetare 3V under normal light conditions.
The hybrid powers supply uses a 1.5V coin battery as a backup power as well.

Processor from Hitachi model HD62021A04 able to work with 1.5V.
The hybrid power supply takes a 3V solar panel and a 1.5V battery as input to a couple of silicon diodes a two resistors and two capacitors.

Hybrid power supply:
Diode MA700 has a Vf=0.5V
Diode MA723 has a Vf=0.3V
Probably both are schottky diodes.