![]() SN=2942S30206 (The housing was exchanged for the one of the 42s that the key-switch was repaired before.) In the processor, was solved by using voltage doubler circuit instead.įor that purpose, the oscillator monitor output is used as its power source. The sticking-to-low-contrast LCD problem, caused by broken switching transistor Membrane switch transplantation to repair the dead key switch of the HP-42SĪ work-around for sticking-to-low-contrast LCD problem of the HP-42S 17 2020 : Pin assignment of the L1R2 corrected. HP 42S partial schematic (Connections to the LCD are omitted) Press, and simultaneously to put it into deep sleep mode. Upon the capacitors to avoid accidental short circuit. Tough insulation tape such as Kapton® tape should be applied on the backplate If you have replaced the 100μF solid tantalum capacitor with MLCC capacitors, *note13 : Apply Kapton® tape to the back plate I idle ≈ 380μA(typ.) (340μA/minimum contrast ~ 420μA/maximum contrast, Diode=BAR43CFILM) I idle ≈ 440μA(typ.) (400μA/minimum contrast ~ 540μA/maximum contrast) HX56N (Not recommended, use Citizen CFV206 65.536KAZF-UB or EPSON C-2 65.5350K-P for new modification),.The parts used for this modification are: It works fine at the double speed, but was unable to be set to the "fast mode", so far.Īnd also can be set to the fast mode without problem. I've done the same modification shown above on the other earlier model of the 42S (firmware revision A). Modification on the earlier model of the 42S I idle ≈ 440μA(typ.) (420μA/minimum contrast ~ 520μA/maximum contrast, Diode=BAR43CFILM) I idle ≈ 440μA(typ.) (420μA/minimum contrast ~ 560μA/maximum contrast) Self-Diagnositic-test (+) results at various frequency and voltage (T a=27☌) Quadruple speed of the original 42S with fresh batteries. This modified 42S was able to execute the user program without error at With setting the speed register at 0x40300 to 0xF by using the built-in debugger, Transmission line parameters were as might be expected. Self-test result was OK, and the results of a user program which solves some *note5 : Nominal capacity of SR44 is 165mAh.Ĭrystal resonator replacement for double speed 42S You can add 100nF to 1μF MLCC capacitor on the padsīetween RAM and the processor for its power supply decoupling. The Vdd noise at SRAM is not reduced so much by this capacitor replacement,Īs it's not intended. Original part pads do just fit to these C3225 size capacitors by a very narrow margin. TDK (part code are shown below), so they are rather expensive yet. The capacitors that I used here are brandnew, high performance capacitors from The other 10μF/16V capacitor is used as the filter of the voltage step up converter for LCD. The larger 100μF/6.3V capacitor is used as the power supply decoupling, and You can reduce its leakage current and also improve its life and reliability. *note3 : Capacitor replacement (Optional)īy replacing these solid tantalum capacitors to multilayer ceramic capacitors, The Vdd noise at SRAM is acceptable and the RAM_WR waveform is not so bad. These waveform were measured while executing the test program shown below. The photo is the waveform of that point showing its frequency ofģ2.78kHz (actually 32.768kHz measured by a frequency counter). There is a testpoint next to the crystal that seems to beĪ buffered output of the clock oscillator. ![]() The other way to make an HP 42S nonvolatileĬhange the jumpers then install a 32KB SRAM,.Double speed HP 42S with 32KB of nonvolatile RAM and protection diode.Double speed HP 42S with 32KB of nonvolatile RAM. ![]() ![]()
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