Service manual

STP 11-25R13-SM-TG
3 - 24
Performance Steps
NOTE: The bias is an ultrasonic signal impressed on the tape along with the input signal to eliminate
distortion.
( c) Check that the REC switch is clean. If behavior changes with each activation of the
record switch, spray contact or tuner cleaner, using an extension tube, inside the
switch (with power OFF). Put the switch through its motions several times and allow
drying before powering back up.
( d) If the ATR is portable or subject to abuse, check for bad connections, especially if
one channel comes and goes.
( e) Measure the signal going to the record heads while in the REC mode. If either high
frequency signal or input signal is absent, trace back to its source following the
schematic.
(7) Troubleshoot an erratic autoreverse problem.
NOTE: Some autoreverse ATRs use a rotating magnet under or as part of each reel and a reed switch or
hall effect device to detect lack of motion and autoreverse. Others are entirely mechanical and may act
erratically if there is dirt, loose belts or idlers, broken parts, or a lack of lubrication.
( a) If the ATR will run without a tape in place, see if the take-up reel rotates properly and
whether the reverse still occurs.
( b) If reel rotation is normal but it still reverses, check the optical tape end sensor or reel
rotation sensors.
( c) If the take-up reel does not rotate, check for bad belts or idler tire.
4. Isolate the fault to a component.
a. Perform resistance and continuity tests with a multimeter.
b. Perform power distribution voltage tests.
c. Check pre-equalization with a multimeter.
5. Replace, repair, or adjust faulty component.
a. Correct a mechanical error.
(1) Clean and lubricate necessary mechanisms.
(2) Replace loose belts and springs.
b. Resolder cold solder joints, being careful not to cause any solder bridges.
c. Replace a tape head.
(1) Remove the tape cover and position the ATR for easy access to the tape head.
(2) Draw a pictorial diagram of the connections before removing the electrical connections.
(3) Remove the tape head from the mount.
(4) Install the replacement head to the mount.
( a) Connect the electrical wires to the terminals in the same configuration as removed.
( b) Protect the tape head from heat damage by using a heat sink when soldering.
(5) Demagnetize the replacement head (according to procedures stated in PMCS task 113-
575-3057.
(6) Adjust the head for proper tilt and height while playing the test tape as a reference.
(7) Reinstall the tape head cover.
d. Adjust the ATR to obtain a signal to noise (S/N) ratio of 50 dB in playback and a flat overall
record and playback frequency response throughout the audio range.
e. Adjust tape transport azimuth.
(1) PLAY a recording made on a known good ATR or a commercial tape.
(2) Set the azimuth adjustment for the best sounding and strongest high frequencies, resulting
in the most natural sound. Turn slowly; a 1/16 of a turn is significant. Turn the screw back
and forth and leave it in the best sounding position.
6. Operations check following performance measure 2b; readjust or align as necessary.
7. Complete DA Form 2407 (Blocks 27, 28, and 36).
8. Turn the DA Form 2407 into the supervisor to inspect the work.