Digital Test
Sencore LC53  

Manufacturer: Sencore
Model: LC53
Year: 1980
Schematic: MF, redrawing
Functions: C, L, leakage, ringing test
Display: LED
Digits: 3.5
Logic: CMOS

The Sencor "Z" Meter measures capacitance and inductance. It also includes a leakage measurement for capacitors, performed at selectable operating voltages up to 600V; and a ringing test for inductors.

Note the test leads must be plugged into the BNC jack to zero the meter for small C measurement. The capacitance of the test leads is necessary to bring the zeroing into range.

The manufacturer schematic has been redrawn for clarity.

Internal view from the top, showing what is referred to as the 'digital' board.

Internal view from the bottom, showing the 'analog' board.

Internal view from the front, showing the display board.

The reed relay for the input protection was faulty in this unit. A new relay has been fitted: the blue package located between the switches on the right. The old relay is sitting on the switch just above.

- Unit Log -

Serial Number: 3403863M (RUN 21)
Year of Manufacture: 1980 (IC date codes up to 8045).
Date of Receipt: 2012 Oct (customer repair)
State upon Receipt: Non-functional. Pressing for C value displays -4.1 or so. Zero-adjust has no effect. Intermittently works for some functions.

Date: 2012 Oct
Procedure: Reed relay at input faulty, loose lead on reed switch. Replaced with Clare PRMA 1A05A. Functional.

Date: 2012 Oct
Procedure: Capacitance drifts beyond zeroing range during 1/2-1 hour of warmup. At comparators, Start leads Stop by ~ 1040 uS at power-on, drifts to ~1180. Comparator trip levels seem stable, alternative is unstable charge rate. Hypothesize that Q132 is leaky, temperature test with soldering iron does suggest leakage instability over temperature. 2N3904 that was present replaced with PN2222A.

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Early Digital Test Equipment