SYMPTOMS COLLECTION PROCEDURES
3-1. TROUBLESHOOTING THE AN/TPS-25A RADAR SET
General. Troubleshooting should normally be performed in the following three steps.
(1) Symptoms collection. Use built-in indicators and test equipment to assist in isolating a malfunction to a
specific channel or area within the channel.
(2) Signal tracing. Use the test equipment that is provided to measure voltages and monitor signals within the
suspected area to isolate the malfunction to a stage (by using the detailed circuit diagrams).
(3) Component troubleshooting. Use test equipment that is provided to find the specific component that is
causing the malfunction.
Symptoms Collection Checks and Block Diagrams. The symptoms collection checks and block diagrams are
designed to aid the troubleshooter in the first two steps of troubleshooting, with the greatest emphasis on symptoms
collection (a(l) above).
(1) Isolation to a system. The overall block diagram (fig 1) is divided into nine systems. By performing the
systems checks in the order in which they are presented in paragraph 3-3, a troubleshooter can isolate a
malfunction to a specific system. A check that does not produce the correct result indicates a malfunction
in a particular system. References presented after the correct results (para 3-3) indicate the pages on
which the system checks and block diagrams of the various systems are presented. When the
troubleshooter has isolated a malfunction to a specific system, he then turns to the referenced page to find
the system checks and block diagram for that particular system.
(2) Isolation to a specific stage. The system checks for each system consist of a list of conditions indicating
malfunctions in specific circuits and the key points that the troubleshooter is to test to aid him in locating
the specified circuits. Page references given for each key point indicate the pages on which the detailed
circuit diagrams for the various circuits are presented. The troubleshooter checks the conditions listed (in
the order in which they are presented) until he finds those conditions that most nearly correspond to the
symptoms noted in the radar. He then tests the key points listed to isolate the malfunction to a specific
(3) Signal tracing. To test a key point, the troubleshooter refers to the applicable detailed circuit diagram (on
the page referenced for the key point) and signal traces in the circuit until he notes an indication of a
malfunction. Using the test equipment issued with the radar, he then makes voltage checks and/or
resistance checks to locate the defective or malfunctioning component.
3-2. SYMPTOMS COLLECTION EXAMPLE
Assume that the operator of an AN/TPS-25A radar has reported that the A-scope is blank and the RADIATE light is
Perform the overall systems checks in the order in which they are presented in paragraph 3-3. Each check
must produce all the correct results listed; therefore, the first check that does not produce the correct results is check 6.
Since the A-scope is blank, the radar does not produce the second result listed for check 6. (Audio can be present without