Heathkit IT-22 Capacitor Tester

Heathkit IT-22 | In-Circuit Capacitor Tester

The Heathkit IT-22 Capacitor Tester is an instrument that allows the user to check capacitors without removing them from the circuit or, of course, removed from the circuit. It will disclose open, shorted, or intermittent capacitors and, with just a little bit experience, permits evaluation of possible leakage. This is an easy-to-use tool for taking a look inside vintage equipment; a quick-&-dirty tool for performing in/out-circuit tests of old paper capacitors which are commonly found on 40's, 50's, 60's tube gear. The IT-22 is the CT-1 successor (same instrument with different appearance).

Pics & schematic + info pages

Using the IT-22.

A five-position switch is employed. Center is "AC OFF". At left is "AC ON - CHECK" for "SHORT" with its "TEST" position and at right are the same positions for the "OPEN" test. The switch is spring loaded in the "TEST" position so as soon as you let go it springs back to return to the "CHECK" position. This switch action removes any voltage stored across the capacitor during the test. The operation of the IT-22 is simple but sometimes confusing because when the eye tube closes or remains closed, the test is "OK", but it reflects a negative condition (NO SHORT circuit, NO OPEN circuit).

Before testing, however, make sure the power is off in the equipment being tested.

Switch to "OPEN CHECK" or "SHORT CHECK" position (choose whichever test you want to put in operation first) and allow the instrument time to warm up. Clip the test leads across the capacitor to be checked, then switch to "TEST" position. An OPEN eye in this position always indicates a BAD capacitor, and a fluttering eye always indicates an intermittent capacitor. If the eye CLOSES (or remains closed), then MAKE the OTHER TEST.

It should also be remembered the following...

On IN-CIRCUIT testings may occur false results due stray capacities or if the capacitor to be tested is not sufficiently isolated from its associated components.
Open eye in the "TEST" position always indicates a BAD capacitor.
ELECTROLYTIC capacitors can only be checked for "OPEN" (for "SHORT" they all will be considered shorted).
A SHORTED capacitor tested for "OPEN" will always result "OK" (not open).
An OPEN capacitor tested for "SHORT" will always result "OK" (not shorted).
Therefore, when the first result is "OK", it is mandatory to make the other test.

Specifications and Operation
SHORT test	Heathkit says "up to 20 µF shunted by at least 10 ohms", but only an equivalent resistance greater than 1000 ohms closes acceptably the eye (not shorted indication = OK). -All tipes EXCEPT ELECTROLYTICS. -Test frecuency: 50-60 cycles (AC line). -Test voltage: about 17 volts AC.	-Switch to the left (CHECK-ON). -Clip the test leads across the capacitor to be checked. -Switch to "TEST" position. -Open eye indicates a SHORTED capacitor. -Totally closed eye indicates a "NOT SHORTED" capacitor but it may to be open. -Partially closed eye indicates a possible LEAKY capacitor *1. -Fluttering indicates intermittency.
OPEN test	Specs: "50 pF to infinity shunted by more than: 2000 ohm at 50 pF. 400 ohm at 100 pF. 30 ohm at 350 pF or more." But only an equivalent resistance less than 10 ohms or a capacitance greater than 30 pF closes totally the eye (not open indication = OK). -All tipes of capacitors. -Test frecuency: 19 Mcs (HF oscillator). -Test voltage: Very low (RF current).	-Switch to the right (CHECK-ON). -Clip the test leads across the capacitor to be tested. Red binding post is + (for electrolytics only). -Switch to "TEST" position. -Open eye indicates an OPEN capacitor. -Totally closed eye indicates a "NOT OPEN" capacitor but may to be shorted or leaky. -Fluttering indicates intermittency.
1 This instrument will not check accurately capacitors which are shunted by an inductance if the reactance of the inductance is less than about 30 ohm at the test frecuency (50-60 Hz for the short test, 19 Mhz for the open test). In the "SHORT" test, a partially closed eye may indicate a possible leaky capacitor BUT considering that low reactance at test frecuency (50-60 Hz) of the circuit involved will result in erroneus indications. The existence or importance of the leakage must be confirmed disconnecting one lead and using a condenser checker, like the C-3*.

Tricks & Mods
Tech Notes: 2M2 res (R3) between pins 3 & 4 (plates) determines the level of closure/aperture of the eye tube. If the value is too low, the eye will not open fully and it could strongly overlap when closed. The exact value of this resistor must be adjusted in the "OPEN-CHECK" position: lowering it will increase the eye closure, raising it will increase the eye aperture. The correct adjust is getting the eye near-closed (making an hairline). This adjust, if neccessary, must be accomplished first. 1K5 res (R2) determines the level of closure for SHORT testings. An increased value of this resistor increases the closure of the eye tube, and conversely. Choose a value for getting the eye near-closed (making an hairline) in the "SHORT TEST" position. This adjust must be accomplished after the mentioned above. Usual TLC: - In order to maintain an adequate level of closure/aperture in the eye tube, the 1K5 resistor commented above may be replaced to compensate tube aging. Before doing this, it is recommended to verify possible replacement of R3 by the same reason. - Cleaning, of course.