This article discusses repair and calibration of the EICO 950A Resistance-Capacitance-Comparator Bridge, commonly used as a capacitor tester. Also discussed are the PACO C-20, EICO 950, and EICO 950B tester. The exact EICO 950A unit pictured in the photos below is for sale at $149 plus shipping, rebuilt and calibrated as described below. The PACO C-20 unit is for sale at $139 plus shipping. Extreme caution must be followed with any vintage capacitor tester because very high voltages are present during repair and while operating. They should only be used by knowledgeable technicians.

When the bridge is unbalanced, the magic eye will remain closed.

PACO C-20 tester

Eico offered three models, the 950, 950A, and 950B. They are very similar, and most of this article will be relevant to all three models. Likewise, I have updated this article to include coverage of the PACO C-20 unit, which is almost identical to the EICO 950B.

These models use a balanced bridge that measures capacitance from 10mmf to 5000mf (some models 2000mf) and resistance from 0.5 ohms to 500 Megohms (some models up to 200 Megohms). During component value testing, the magic eye tube serves as the null-indicator. When the bridge is far from balanced, the target area of the magic eye tube glows completely closed green, and in fact overlaps. As the pointer dial approaches balance point, first the overlapping disappears and eventually the entire target area of the eye tube is completely open (dark). The bridge is balanced when the maximum dark area is indicated, and you can then read the value of your component on the faceplate scale. This is a very high quality test instrument when properly rebuilt.

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