HP 83522A Service Notes page 257

Model 83522A
Service
3.
Check TP16. This voltage should track the YO DRIVE V (Figure 8-46). If it
does not, troubleshoot U24, Ql, Q2, A9R1, and A9Ql.
a.
To verify proper operation of U24, ground TP16 (R1 is a 12 Watt
resistor). Press 8350A CW
.
Vary the voltage at U24 pin 3 by
changing the CW frequency as indicated on the front panel. With
TP16 at 0 Vdc, U24 pin 6 should be at approximately +20 Vdc for
positive input voltages, and approximately - 10 Vdc for negative input
voltages. If it is not, replace U24.
b. A9R1 should be checked by removing the A9 assembly from the
instrument. The ohmmeter reading should be approximately 125
ohms.
c. While the A9 assembly is removed from the instrument, check the
collector-base and base-emitter junctions of A9Q1 with an ohmmeter.
These junctions should show only a few hundred ohms when forward
biased, and a high impedance in the reverse direction. If A9Q1 is
found to be shorted or opened, make sure that protection diodes VRl
and CR6 are good before replacing the transistor.
d. Q1 and 4 2 can be checked, using the procedure above, while they are
'
still in the circuit. The line power should be off.
Interrupt Control
Symptoms of an interrupt failure may include loss of sweep, portions of the
sweep trace missing, or a false bandswitch.
1. Place the A6 assembly on an extender board. With an oscilloscope, check
PI-23 (L SSRQ) for approximately +4.5 Volts. Since the band-switch
circuitry is disabled, the only time L SSRQ should be low is when used in
conjunction with external equipment requiring a stop sweep, or when
programmed through the 8350A auxiliary programming connector.
a.
If L RTS is low, check that U5 pin 3 is at 0 Volts. If it is not, check the L
BSE line for approximately +4.5 Volts. Then troubleshoot U26.
b. If U26 is good, ensure that U17A pin 5 is not held high. If it is good,
other lines are probably pulling L SSRQ low. Refer to the 8350A
Operating and Service Manual for more troubleshooting information
to determine the problem.
2. Check edge connector pins PI-3 (LSIRQ) and PI-1 (L RTS).
a. L RTS should appear as illustrated in Figure 8-50 with a low pulse
occuring at the end of each forward sweep. If L RTS is not correct,
trace the problem back through the plug-in interconnects to the
8350A.
b. LSIRQ should pulse low briefly for end-of-sweep interrupts as
illustrated in Figure 8-50. If these pulses are missing, but L RTS is
present, suspect U21C, U17B, or control lines from U22.
c. If L SIRQ stays low, or the pulses are exceptionally wide, check U22
with the procedure outlined under Digital Control section. If U22 is
functioning, the 8350A microprocessor probably did not receive the
interrupt. Trace this signal back to the 8350A.