Service manual

STP 11-25R13-SM-TG
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Performance Steps
b. Perform functional tests on suspected circuits.
c. Signal trace to find where the signal was lost or distorted.
(1) Inject color bars from the VTSG in the RECORD and E-E modes; PLAY a color bars tape
in the Playback mode.
(2) If tape motion is slow or stops completely, check the head drum for a mirror-like surface.
(3) Check tape tension for hooking at the top of the picture.
(4) Check the input amplifier in the first stage of the video record amplifier for video output
with an oscilloscope and compare the readings with the manufacturer's manual.
NOTE: This first stage passes all the information contained in the signal, including the 3.58 MHz color
information and the 4.5 MHz audio-carrier.
(5) Check the low pass filter (LPF) for interference patterns in the final picture with an
oscilloscope.
(6) Check the pre-emphasis circuit with an oscilloscope for noise in the video signal.
NOTE: Pre-emphasis does not remove noise already in the signal, but will eliminate noise introduced by
the VTR electronics.
(7) For severe picture dropout problems, check for dirty brushes or commutator, clogged
video heads, or tracking control out of adjustment.
(8) For excessive H motion of the picture during playback, check for low frequency flutter,
excessive capstan drive pressure, or a damaged capstan drive wheel.
4. Isolate the fault to a component.
a. Perform resistance and continuity tests with a multimeter.
b. Perform power distribution voltage tests.
5. Replace, repair, or adjust faulty component.
6. Clean the video heads, stationary heads, and tape movement area following the procedures listed
for PMCS task 113-575-3050.
CAUTION: Wait until the cleaning fluid evaporates completely before inserting a tape.
7. Operations check by performing the procedures listed in performance step 2b; readjust or align as
necessary.
8. Complete DA Form 2407 (Blocks 27, 28, and 36).
9. Turn the DA Form 2407 into the supervisor to inspect work.
Performance Measures Results
1. Review DA Form 2407. P F
2. Sectionalize the trouble to a defective stage. P F
a. Visually inspect for discrepancies. P F
b. Operations check the VTR. P F
3. Localize the trouble to a specific circuit. P F
a. Analyze overall block diagrams and schematics. P F
b. Perform functional tests on suspected circuits. P F
c. Signal trace. P F
4. Isolate the fault to a component. P F
a. Perform resistance and continuity tests. P F
b. Perform power distribution voltage tests. P F
5. Replace, repair, or adjust faulty component. P F
6. Clean the video heads, stationary heads, and tape path. P F