HP-35 Power Supply Waveforms

[albertofenini]

(04-09-2019 12:49 AM)cruff Wrote:  If the transistor you selected for Q1 is out of tolerance for its operating parameters, as compared to the original type, that might be enough to keep it from performing the regulation function in the way the circuit was designed. If that is the case, then selecting a lower value zener diode would suffice to adjust the voltages down. You could check to see what the waveform on the base of Q1 is doing, perhaps there is not quite enough drive current to switch Q1 on more fully to reduce the Vss voltage, and indirectly the other two voltages. Also verify that R1 is close to the listed value on the schematic.

Thanks for the idea, Q1 is actually an old original 0550,
I'll check the HFE and I'll check the R1 value but I'm pretty sure is close to what it should be, and this R1 is also from an old logic board
I'll also check the waveform on the base of Q1
thx !!