Table of Contents
Advertisement
Next, remove the top and bottom covers and inspect for
open connections, charred components, or any other
visible defects. If the trouble source cannot be detected
by visual inspection, proceed to step (2).
(2)
In almost all cases, the trouble can be caused by
incorrect dc bias or reference voltages; thus, it is a good
practice to check the voltages in Table 5-2 before proceed¬
ing with step (3).
(3)
Disconnect the load and examine Table 5-3 for
your symptom and its probable cause.
5-56
Table 5-3 contains symptoms and probable causes
of many possible troubles. If either high or low output
voltage is a symptom, Table 5-4 contains the steps necessary
to isolate the trouble to one of the feedback loops and
instructions directing the tester to the proper table for
further isolation. Because of the interactions between loops,
it is necessary to refer to Table 5-4 before proceeding to
Tables 5-5, 5-6, or 5-7.
5-57
Tables 5-5, 5-6, and 5-7 contain troubleshooting
procedures for the series regulator and preregulator feed¬
back loops once the fault has been isolated to one of them.
Tables 5-5 and 5-6 contain instructions for driving each
stage into conduction or cut-off. By following the steps in
these tables, the fault can be isolated to a circuit or a
component.
5-58
Table 5-7 contains troubleshooting procedures
for the preregulator feedback loop. Troubleshooting is
accomplished by comparing waveform illustrations with
the waveforms found at various test points and then
checking the components most likely to be at fault.
5-59
After troubleshooting the unit, it may be necessary
to perform one or more of the calibration procedures
given in this section.
WARNING
Some circuits in this power supply are connected
directly to the input ac power line. The red-
painted case and heatsink of the A2 RFI Assembly
are also at ac line potential. Exercise extreme
caution when working on energized circuits.
Table 5-2. Reference and Bias Voltages
(Refer to schematic and component location diagrams in Section VII for test point locations)
STEP
METER
COMMON
METER
POSITIVE
—
NORMAL
VDC
NORMAL
RIPPLE (P-P)
PROBABLE CAUSE
1
(Ts]
TP63
1 2.4 ±7%
2.0m V
CR61, CR62, Q60, Q61, Q62, Q63
2
(Ts)
TP64
6.2 ±5%
0.5mV
VR60, VR61, R63
3
TP65
(+s)
6.2 ±5%
2.0mV
VR60, VR61, R63
4
Its]
TP66
11 ±15%
2.0V
CR53, CR54, C44
5
TP67
4.0 ±12.5%
0.8V
CR53, CR54, C44, CR45-49
6
TP68
©
2.4 ±12.5%
0.4V
CR53, CR54, C44, CR45-49
Table 5-3. Overall Troubleshooting
SYMPTOM
PROBABLE CAUSE
Low or no output voltage
(OVERVOLTAGE lamp
may be on or off).
a. Front panel meter defective.
b. Crowbar not reset or defective. Refer to Table 5-4.
c. Series regulator or preregulator feedback loop defective. Refer to Table 5-4.
High output voltage
a. Front panel meter defective.
b. Series regulator or preregulator loop defective. If crowbar does not trip,
it too is faulty. Refer to Table 5-4.
c. Open circuit between sensing terminals (±S) and output terminals
(±OUT). Refer to Table 5-4.
5-9
Advertisement
Table of Contents
