Sencore LC77 / LC102
Sencore LC77 / LC102 is rare device, but don't have competitors nowadays.
I buyed this device without power adapter and battery.
I made a new battery based on Hakadi 3000 mAh 21700 LiFePO4 cells with TL431 based balancers (balancing voltage 3.4V) to replace original Pb BY234 battery.
Cable with jack (6.3x3mm if i remember correctly) was used from old Toshiba laptop PSU.
To support this battery type - on power supply(leakage supply) board IC5 output voltage must be changed by R40 to 14.2 V.
Also on this board low voltage electrolytic capacitors was replaced by new ones. CR10 replaced by HER208, CR11 replaced by 1.5KE68A.
Original PA251 / PA252 power adapter is unregulated. We can use PSU with min voltage 17 V, max 25 V.
PA251 / PA252 adapter has mini iec connector. Mini iec connectors can be easily found in psu for zyxel 33k modems (u-336e for example). PSU part number DVE DV-2190ACUP, ZyXEL A482109 etc.
I have done power adapter with this connector from zyxel:
Also to improve accuracy and stability of measurements (especially on battery supply) some modification was done to ADC reference.
1N825 zener is good for reference, but need constant current around 7.5 mA through it to obtain good voltage and temperature stability.
So R50 on the main board was replaced by constant current source based on LM317L + 160 ohm resistor.
Adjustment was made using GenRad standard capacitors (0.05%) and SSSR standard inductors (0.02%).
Calibration after 1 year shows that capacitance measurement accuracy is better than +-0.2%, inductor better than +-0.4%.
Sencore LC77 Operating manual.
Sencore LC102 Operating manual.
Sencore LC77 Calibration procedure.
Sencore LC77 / LC102 circuit description.
Sencore LC77 schematics sheets.