Service manual

STP 11-25R13-SM-TG
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REPAIR A VIDEO TAPE RECORDER/REPRODUCER (VTR)
113-575-0056
Conditions: In a tactical or garrison environment, given an inoperable or malfunctioning VTR submitted
for repair on a DA Form 2407, a known good VTR, dual-trace oscilloscope with 10X test probes,
multimeter with test leads, video audio test signal generators, network analyzer, color TV receiver (or
color monitor, audio amplifier, and speakers), WFM, vectorscope, alignment and work tapes, electronic
equipment tool kit, soldering tool kit (light to medium duty), Tentelometer-type instrument (or dummy reel
and a spring gauge), bench stock (for replacement parts), manufacturers' manuals, and DA Pam 738-
750.
Standards: The standards are met when the VTR plays and records tapes without error.
Performance Steps
1. Review DA Form 2407.
2. Sectionalize the trouble to a defective stage.
a. Visually inspect for physical damage, missing controls, broken switches, cracked components,
loose connectors, unseated boards, and other discrepancies.
b. Operations check the VTR to verify that the deficiency or symptom exists and to what extent.
(1) Turn ON VTR power.
NOTE: If the VTR has self-diagnostics, an error code number appears on the tape counter display when
the VTR cannot operate normally due to a certain error. Follow error flow charts in the manufacturer's
manual.
(2) To remove a stuck tape, cycle power ON and OFF to reset the internal microcontroller. If
unsuccessful, remove the VTR cover and manually turn the threading ring belt to unthread
the tape.
(3) Set all controls and switches to desired settings; check Dial Menu and Time Code
settings, if available.
(4) Check Playback mode.
( a) Connect the VTR outputs to a WFM, vectorscope, and color receiver (or color
monitor, audio amplifier, and speakers).
( b) Insert and PLAY an alignment tape with 1 kHz audio tone at 0 VU and color bars, 1 V
P-P at 140 IRE.
( c) Verify the VTR outputs using the monitoring equipment.
( d) Check the VTR Tracking meter for an indication of 4.
( e) Check that the Servo lamp lights indicating that the drum servo and capstan servo
are locked.
NOTE: When playing an alignment tape, low off-tape RF level with peaked tracking indicates worn video
heads in need of replacement. Tearing or bearding during video playback with sharp, dark-to-white
transitions also indicates a worn head.
(5) Check the E-E mode.
( a) Connect audio video signal generator(s) to the VTR audio and video inputs.
( b) Turn ON power to the signal generator(s) and check the VTR Video and Audio
meters for correct signal modulation.
( c) Verify the signal generator outputs through the VTR using the monitoring equipment.
Audio should be 1 kHz tone at 0 VU. Video should be color bars, 140 IRE at 1 V P-P.
(6) Check the Record mode.
( a) Insert a work tape and RECORD for one to two minutes.
( b) Check the VTR Video and Audio meters for correct signal modulation.
( c) PLAY the recorded tape on a known good VTR to check interoperability.
c. Define what the problem is and in what mode the problem occurs.
3. Localize the trouble to a specific circuit.
a. Analyze overall block diagram and schematics.