Service manual

STP 11-25R13-SM-TG
3 - 26
REPAIR A DISTRIBUTION AMPLIFIER (DA)
113-575-0048
Conditions: In a tactical or garrison environment, given a distribution amplifier with a reported fault
written up for maintenance on a DA Form 2407, audio or video test signal generator (depends on type of
distribution amplifier), dual-trace oscilloscope with 10X test probes, multimeter with test leads, electronic
equipment tool kit, soldering tool kit (light to medium duty), bench stock, system block diagrams,
manufacturers' manuals, and DA Pam 738-750.
Standards: The standards are met when the distribution amplifier passes the signal at each output at the
same level as the input: video at 140 IRE (1 V P-P) or audio at +4 dBm (0 VU).
Performance Measures Results
1. Review DA Form 2407. P F
2. Sectionalize the trouble to a defective stage. P F
a. Visually inspect for physical damage, missing controls, broken switches, cracked
components, loose connectors, and other discrepancies.
P F
b. Turn ON and operations check the distribution amplifier to verify that the
deficiency or symptom exists and to what extent.
P F
c. Inject a signal at the distribution amplifier input and check each output for the
same level as the input.
P F
(1) For VDAs, connect color bars (140 IRE at 1 V P-P) from the VTSG. P F
(2) For ADAs, connect a 1 kHz tone at +4 dBm from the ATSG. P F
3. Localize the trouble to a specific circuit by analyzing overall block diagrams and by
performing functional tests on suspected circuits.
P F
4. Isolate the fault to a component. P F
a. Perform resistance and continuity tests with a multimeter. P F
b. Perform power distribution voltage tests. P F
5. Replace, repair, or adjust faulty component. P F
a. Align the distribution amplifier power supply by using the multimeter voltage
function and adjusting the appropriate trim pot with an alignment tool.
P F
b. Adjust the input level trim pot with an alignment tool while monitoring the
oscilloscope.
P F
NOTE: The input and output adjustments can also be performed using a WFM for VDAs
and a VU meter for ADAs.
c. Adjust output level trim pots with an alignment tool while monitoring the
oscilloscope.
P F
6. Operations check by injecting a signal at the input and checking each output for the
same level as the input: video at 140 IRE (1 V P-P) or audio at +4 dBm (0 VU);
readjust or align as necessary.
P F
7. Complete DA Form 2407 (Blocks 27, 28, and 36). P F
8. Turn the DA Form 2407 into the supervisor to inspect work. P F
Evaluation Guidance: Score the soldier a GO if all steps are passed (P). Score the soldier a NO-GO if
any step is failed (F). If the soldier fails any step, show what was done wrong and how to do it correctly.
Have the soldier practice until he can correctly perform the task.