SYMPTOMS COLLECTION PROCEDURE
Section I GENERAL INSTRUCTIONS
TROUBLESHOOTING THE AN/MPQ-4A RADAR SET
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 to a specific 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 (usually performed by using the detailed schematic).
(3) Component troubleshooting: Use the test equipment that is provided to find the specific component that is
causing the malfunction.
The symptoms collection block diagram and charts are designed to aid in the first two steps of
troubleshooting, with the greatest emphasis on step (1) in a above (symptoms collection).
(1) Isolation to a system: The overall block diagram is broken down into NINE systems. By performing the
given checks in order, a malfunction can be isolated to a channel. A bad check indicates a malfunction in that particular
(2) Isolation to a system (overall block diagram, fig 1): Advance to the block diagram of that particular system.
These blocks show the general operation of that particular system and the necessary checks to make in the system. ALL
CHECKS SHOULD BE MADE IN THE ORDER GIVEN, USING THE INDICATORS THAT ARE PROVIDED ON THE
SYSTEM, ALONG WITH TEST EQUIPMENT.
Signal tracing is performed by using the block diagram and detailed circuit. As an aid in circuit location, there is a
column in the block diagram chart headed KEY POINTS. Key points are listed for each circuit. Along with each
key point is the circuit diagram page number on which the key point is located.
3-2. GENERAL SYMPTOMS COLLECTION INSTRUCTIONS FOR THE AN/MPQ-4A RADAR SET
The three steps of general symptoms collection are as follows:
(1) Upon verification of a symptom, perform symptoms collection checks on the AN/MPQ-4A overall block
diagram (fig 1). Perform these checks in order, starting with paragraph 3-3, until a bad indication is found.