You now turn to the page referenced after result b of check 6 (page 29). Presented on pages 29 and 30 are the system
checks and block diagram for the transmitter and RF systems; therefore, you have isolated the malfunction to these
Now you must isolate the malfunction to a specific stage within the transmitter and RF systems. To do this,
you check the conditions listed in paragraph 3-8 (in the order in which they are presented) until you find the conditions that
most nearly correspond to the symptoms noted in the radar--the last conditions presented in paragraph 3-8. You then test
each of the key points listed for these conditions.
Using the detailed circuit diagrams on the pages referenced (pages 35 and 58), you signal trace until you find
the malfunctioning stage. Then, using the test equipment provided with the radar, you make the necessary voltage checks
and/or resistance checks to locate the defective or malfunctioning component.
(1) Upon verification of a symptom, perform symptom collection checks on the AN/TPS-25A overall block
diagram. Perform these checks in order, starting with check one until a bad indication is found.
(2) Go to the block diagram of the bad system or channel noted in step (1). Make checks in the order given
until a good indication is found. This will tell you the channel that is malfunctioning.
(3) 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.
Following is an example of general symptoms collection: SYMPTOM: AN/TPS-25A operator reports that the
A-scope is blank and the radiate light stays on.
(1) Perform all check number steps on the overall systems checks until you have reached step 6 which is
labeled RADIATE switch to the ON position. Perform all check number sub-steps to get complete
symptoms. (Audio can be presented without a sweep. Check number sub-step 6b is the first adnormal
(2) You are now using the block diagram for the transmitter and RF control circuits. Select the conditions that
most closely correspond to the symptoms and perform the key point tests by going to the page shown to
the right of the selected key point. When you find a fault indication, stop and go to the detailed circuit. (All
conditions in the check column must be met). Blank scope is any scope that does not have a horizontal
(3) Begin signal tracing on the detailed circuit diagram until you get a bad indication, using the KEY POINTS
that are provided. When a bad check is noticed, signal trace down to the stage. Once the stage is found,
determine what is causing the stage to malfunction. Use the test equipment that is provided with the