Keysight 11683A, Руководство по эксплуатации и обслуживанию

Страница: 47 / 53

Service 6
Keysight 11683A Operating and Service Manual 47
A3 sampling gate assembly
The input to the A3 assembly is no15.8 mVdc with the RANGE switch set to a 100 mW.
The multivibrator drive from the Power Meter to the FET Sampling Gate circuit may be checked on
pins 4 or 6 of U1. This drive voltage is a 220 Hz square wave whose most positive level is -0.05
±0.05 Vdc with the most negative level >9 V more negative.
In most cases it may be assumed that the operational amplifier, made up of the Input Amplifier and
the first amplifier in the Power Meter, is operating correctly if the dc voltage found on the metal
cover of A3A1Q1 is -70 ±30 mVdc.
The FET's in A3A1U1 may be checked by the following procedure:
1 Disconnect the cables from the 11683A.
2 Remove the upper chassis from the A3 assembly. (Refer to disassembly procedures.)
3 Measure the resistance between pins 1and 2 of the A3A1U1. The resistance should be
15 ±0.75 ohms. The same resistance should be found between pins 8 and 9 of A3A1U1.
4 Short pins 4, 6, and 9 of A3A1U1. While the pins are shorted, measure the resistance be ­ tween
pins 2 and 3, and between pins 3 and 8, of A3A1U1. The resistance should be less than
40 ohms.
5 Set a power supply to 10 Vdc.
6 Connect the positive side of the power source to A3J1 pin E signal ground. Connect the
negative power supply lead to pins 4 and 6 of A3A1U1.
7 Measure the resistance between pins 2 and 3 of A3A1U1. Also measure the resistance between
pins 3 and 8 of A3A1U1. In both cases, the resistance should be several hundred times the
resistance found in step 4 .
If A3A1U1 is replaced it is recommended that the FET BALANCE ADJUSTMENT be performed to
ensure the 11683A is operating at maximum capability.
A4 power switch and rear panel assembly
In 2017, the 11683A and 11683AZ-H01 had a new power switch design. If the user replaces the old
power switch with the new design (11683-60004), the old rear panel should be replaced with the
new rear panel as well.
The new rear panel has switch bracket opening in a vertical position compared to the old design
which opened horizontally.
Part numbers for the new power switch design and the new rear panel design are as follows:
– 11683A-FG: 11683-60004 (New Power Switch) + 11683-00001 (New rear panel)
– 11683AZ-H01: 11683-60004 (New Power Switch) + 11683-00012 (New rear panel)
NOTE
The following instructions apply after the A3Al Circuit Board Assembly has been exposed. Refer
to “Disassembly of A3 sampling gate assembly” on page 43.