Cv/Cc Status Annunciators Troubleshooting; A5 Control Board Troubleshooting Setup; A3 Fet Board Troubleshooting - Agilent Technologies 6571A Service Manual

CV/CC Status Annunciators Troubleshooting

When troubleshooting the CV/CC status annunciators or status readback circuits, first measure the voltage drop across the
gating diodes, which are A5D615 for the CC circuit and A5D620 for the CV circuit (see A5 Control Board schematic
diagram, Sheet 2). A conducting diode indicates an active (ON) control circuit. This forward drop is applied to the input of
the associated status comparator (A5U630) and drives the output low. The low signal indicates an active status which is sent
to the secondary microprocessor A5U504 via Programmed GAL A5U502 (see schematic Sheet 1). The front panel CV
annunciator lights when the CV mode is active (CV is low) and the CC annunciator lights when the CC mode is active (CC
is low). If neither is active, the UNREGULATED (Unr) annunciator comes on.

A5 Control Board Troubleshooting Setup

Several troubleshooting procedures in this chapter require you to gain access to the components and test points on the A5
Control Board. To do this, follow the procedure given in Table 3-3.
To gain access to components and test points on the A5 Control Board, proceed as follows:
1. Turn off power supply and remove the top cover and RFI shield (see Disassembly Procedures).
2. Remove the A5 Control Board from the output subchassis (see Disassembly Procedures).
3. Lay the board, component side up, on a piece of insulating material adjacent and close to the supply.
4. Make the following connections;
a. Ribbon cable W3 from A5J509 to A4J500.
b. Phone cable W4 from A5J502 to A2J107.
c. Test cable (2-wire cable assembly Agilent P/N 5080-2169) from A5J503 to A3J200.
d. Make a 12-inch test jumper cable from two 20-pin connectors (Agilent P/N's 1251-8666 and 1251-8667) and 20
feet of wire (24-26 AWG). Use the cable to connect A5J510 to A6J900.
You may now proceed with the specific tests for the A5 Control Board.

A3 FET Board Troubleshooting

Because test points on the FET board are not accessible when the board is installed, troubleshooting must be performed with
the board removed from the power supply. Both static (power removed) and dynamic (power applied) troubleshooting
procedures are provided. The location of different test points are shown by encircled numbers on the A3 FET Board
schematic and component location diagrams (see Chapter 6).
Note
If any power FET (Q201-204, Q211, Q222, Q233 or Q244) is defective, you must replace all eight with a
matched set.
1. Turn the power supply off and remove the A3 FET board with its heatsink assembly
attached (see "Disassembly Procedures").
2. Measure the resistance between the + Rail (E502) and the - Rail ( E501).
3. Measure the resistance between the gate of each FET (Q201-204, Q211, Q222, Q233,
and Q244) and common (-Rail).
Table 3-4. FET Troubleshooting Chart
Procedure
Static Troubleshooting
Result
≥ 20 MΩ.
>15 kΩ.
Troubleshooting 53