Go to the block diagram of the bad system or channel noted in paragraph 3-3. Make checks in
the order given until a bad indication is found. This will tell you which channel is malfunctioning.
Using the key points associated with the circuit being checked and the page reference, go to the
detailed circuit and signal trace in that circuit until a bad indication is found. At this time you should
be able to locate the bad stage or component with the test equipment issued with the radar.
The following is an example of general symptoms collection:
AN/MPQ-4A operator reports that the B-scope is blank.
Perform all steps on the overall block diagram (para 3-3, fig 1) until you reach paragraph 3-7,
which is titled INDICATOR SYS- TEM. Paragraph 3-7 on the overall block will refer you to figure 5.
(Paragraph 3-7 is the first place you had a bad indication. )
You are now using the block diagram for the SYNCHRONIZER AND INDICATOR SYSTEMS.
Perform all steps indicated on the left. When you find a bad indication, stop and go to the detailed
circuit in the CD Manual. (ALL CONDITIONS IN THE CHECK COLUMN MUST BE MET. ) Blank
scope is any scope that has any abnormal condition and that does not have a short gate, range
strobe, azimuth strobe, noise, and STC action. If the transmitter will energize and the scope is
blank, you must assume that the STC is working.
Begin signal tracing on the block diagram until you get a bad indication, using the KEY POINTS
that are provided. When a bad check is noticed, refer to the CD Manual on the page given and
signal trace down to the stage. Once the stage is found, determine what is causing the stage to
malfunction, using the test equipment that is provided with the AN/MPQ-4A radar.
Test points and waveforms are color coded as follows:
setting, 5K u sec.