HP 15C - LC resonator replacement for triple speed 15C
hp15c-0.jpg
Takayuki HOSODA
Oct. 12 2009
Japanese Japanese edition is here.

Triple speed modification (#2614A06612)

Internal view of the original HP 15C (Serial#=2614A06612, CPU=1LM2-0001)

Power supply current (Ta=26°C, Vbattery=4.72V(SR44×3), fLC=884kHz(original))
Internal view of the modified HP 15C (Serial#=2614A06612, CPU=1LM2-0001)

Parts replacement Parts addition
Results (Ta=27°C, Vbattery=4.7V, fLC)

Power supply current (Ta=27°C, Vbattery=4.5V(SR44×3), fLC=2.8MHz)

Triple speed modification (#2813A62318)

Internal view of the original HP 15C (Serial#=2813A62318, CPU=1LM2-0001)

Internal view of the modified HP 15C (Serial#=2813A62318, CPU=1LM2-0001)

Parts replacement Parts addition
Results (Ta=27°C, Vbattery=4.76V, fLC)

Experimental modification for quad-speed 15C (#2813A62318)

Internal view of the modified HP 15C (Serial#=2813A62318, CPU=1LM2-0001)

Parts replacement Parts addition
The self-diagnostics-test ([ON]+[×]) results at various voltage and LC conbination, and N-queens benchmark results.
Ta=27°C Osillator inductor and capacitor Comment
47μH, 47pF 47μH, 33pF 47μH, 27pF
Vbattery IbatteryResult IbatteryResult IbatteryResult
4.7V 2.9mAO.K. 3.2mAO.K. 3.4mAO.K. Nominal voltage of SR44×3 at 20°C
3.8V 2.1mAO.K. 2.4mAO.K. 2.5mAO.K. Cut-off voltage of SR44×3 at -10°C
3.6V 2.0mAO.K. 2.2mAO.K. 2.5mAO.K. -
3.5V 1.9mAO.K. 2.1mAO.K. 2.2mAO.K. Low battery indicator turns on when
Vbattery ≤ 3.5V
3.4V 1.9mAO.K. 2.0mAO.K. -FAIL
3.3V 1.8mAO.K. -FAIL -FAIL
3.2V 1.7mAO.K. -FAIL -FAIL
3.1V 1.6mAO.K. -FAIL -FAIL
3.0V -FAIL -FAIL -FAIL
2.7V
Cut-off voltage of LR44×3 at 20°C
tN-queens 23m15s 20m30s 19m25s Vbattery=4.7V, Ta=27°C

Conclusion

The triple-speed-modified HP-15C with 1LM2 processor seems works well, and stable as far as you are using SR44 (Zink Silver Oxide) batteries.
The recommended parts value for the LC resonator are 47μH and 68pF so far.
At least one bypassing MLCC (Multi Layer Ceramic Capacitor) of its value from 1μF to 10μF should be added to the power line for stable operation.

SEE ALSO

REFERENCE


APPENDIX - Program library


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