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Make most voltage measurements (except DC-to-DC Converter and ac mains-connected circuits) referenced to the unit's
output common. The output common is accessible at rear-panel
M terminal. All voltages are ± 5% unless a range is
given.
Using the Tables
Typically there will be two types of power supply failures; no-output and performance failures.
1.
NO-OUTPUT FAILURE: Start with the TROUBLESHOOTING NO-OUTPUT FAILURES section which
references Tables 3-1 and 3-3.
2.
PERFORMANCE FAILURE: If the power supply produces an output but does not perform to specifications, begin by
verifying the measurements at the A2J7 test connector using Table 3-1. Next, verify the front panel by doing the
procedure outlined in the FRONT PANEL TROUBLESHOOTING section. After the front panel has been verified
consult Table 3-5 for the performance failure symptom which seems closest to the one observed and proceed to the
functional circuit given for that failure.
The circuits referenced in Tables 3-2 and 3-5 are derived from functional blocks of circuits in the power supply. These
blocks are given in the Power Supply Blocks section starting on page 40. Troubleshooting information for each block will
include a brief description of the circuit involved. The columns provided in each block are as follows:
NODE: This column lists the nodes where the measurements should be taken. In some cases this will be
stated as NODE ( + ) and NODE (- ) where the first is the test node and the second is the
reference.
SETUP: If a certain setup is required for the measurement, it will be given in this column.
MEASUREMENT: This column indicates what the expected measurement is for the given node.
SOURCE: If applicable, the components which generate the signal will be provided in this column .
Some blocks will have Input and Output sections. The input section will have a source column to indicate which
components generated the measured signal. The output section will list all the important output signals from that block.
However, because the outputs of one block are the inputs to another, the schematic should be consulted if an output
measurement is incorrect. This will indicate the next circuit block to be trouble shot.
Main Troubleshooting Setup
Figure 3-1 shows the troubleshooting setup for troubleshooting all of the unit except the front panel and initial no output
failures (see page 36). The external power supply provides the unit's internal bus voltage. The ac mains cord connects to the
unit's A1T3 bias transformer via an isolation transformer, thereby energizing the bias supplies, but it does not connect to the
input rectifier and filter because that would create the bus voltage. With the external supply the unit operates as a dc-to-dc
converter. The supply biases the A4Q1, A4Q2, A4Q3 and A4Q4 PFETs with a low voltage rather than the 320Vdc bus
voltage. This protects the PFETs from failure from excess power dissipation if the power-limit comparator or the off-pulse
circuitry are defective. It also reduces the possibility of electrical shock to the troubleshooter.