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Troubleshooting
Component-level Troubleshooting
5
5-83
J201. The +PA supply (at +180V)should go into current limit. The oscilloscope
should show a repeating pattern in which the +PA supply climbs to about +180V
then drops to 0V. If a failure is detected, check Q203, VR246, VR213, U201C, and
associated components.
10. Check the unregulated -250V Supply. Using a DMM, measure the dc voltage at
TP212 and verify it is -280V ±10%. If a failure is detected, measure the voltage at
the anode of VR231 and verify it is-140V ±20%. If this voltage is incorrect, check
VR231, VR230, VR229, VR225, and Q209. If the voltage at the anode of VR231 is
correct, then check Q215, CR234, CR235, CR239, CR243, and associated
components.
11. Check the regulated -PA Supply at 0V. Using a DMM, measure the dc voltage at
TP204 and verify it is less than 1.0V. If a failure is detected, check Q212.
12. Check the regulated -PA Supply at -180V. Jumper TP207 to PACOM (TP203),
measure the -PA Supply at TP204 and verify it is -190V±10%. If this voltage is
correct, skip to step 13, otherwise continue as follows. Measure the output of the
Current Limit circuit. Connect a DMM to pin 2 of U201 and verify it is +12±4V. If
this voltage is incorrect, then the -PA Supply is in current limit. Check the output for
shorts and check the current-limiting circuit contained in U201D, Q211, Q214, and
associated components. If the voltage at pin 2 of U201 is correct check Q210, Q216,
VR232, VR238, and associated components.
13. Check the unregulated -PA Supply at -360V. Jumper TP207 and TP208 to PACOM
(TP203), measure the voltage at TP212 and verify it is-480V ±10%. If a failure is
detected, check Q209, VR225, VR229, VR230, CR234, CR235, CR239, CR243, and
associated components. Next, check the regulated -PA Supply at TP204 and verify it
is -370V±10%. If a failure is detected, check Q210, and VR226.
14. Check the Current Limiting of the -PA Supply. Jumper TP207 to PACOM (TP203)
and remove the jumper connecting TP208 to LO HI I (TP206). Connect an
oscilloscope to the -PA Supply at TP204. Connect a 1 kΩ 10W resistor (such as
Fluke P/N 157933) between PACOM (TP203) and the -PA supply output at Jumper
J202. The -PA supply (at -180V)should go into current limit. The oscilloscope
should show a repeating pattern in which the -PA supply climbs to about -180V then
drops to 0V. If a failure is detected, check Q214, VR247, VR233, U201D, and
associated components.