HP 5334B Service Manual page 163

8-312. If the Coupling function is defective:
a. Check the relay control line at K5, pin 6 (or anode of CR32). When togglmg the AC button, the volt-
age measured should switch from a l T L HIGH level in the AC mode to a l T L LOW level in the DC
mode.
b. Measuring the correct voltages at anode of CR32 indicate a defective relay, while incorrect voltages
possibly indicate a defective driver (U37) or buffer gate (U38C).
8-313. To check the 50R11 MR IMPEDANCE function:
a. Remove any input from the Counter.
b. Set 5334B to the dc coupling mode and toggle the 50R key. Measure the input resistance at the Chan-
nel A Input connector for each setting with a DVM or DMM. (Measure from the BNC connector
center pin to Ground.)
c. The 50R impedance should measure to within
+
50, and the 1 M51 impedance should be correct to
within
+
10
kil.
8-314. If the input resistance does not change as the 5051 key is pressed:
a. Check the control voltage at pin 3 of relay K6 (or anode of CR33). The voltage should switch from a
TTL HIGH level in the 1 M51 mode to a TTL LOW level in the 50R mode.
b. If this line toggles correctly, it indicates that relay K6 is defective. An incorrect voltage measured
here indicates a defective drive output from U37. Should the impedance measurements be out of
tolerance, check the appropriate resistors for any shorts or opens.
Resistor Combinations:
5051
-
made up of R120 and R121 in parallel.
1 MR in X1 Attenuation mode
-
series combination of R108,109, 110, and 95.
1 MQ in XI0 Attenuation mode
-
series combination of R116 and R93.
8-315. The XlIX10 ATTENUATION function can be checked:
a. Apply a 100 kHz, 1 volt peak-to-peak sine wave signal to the Channel A Input.
b. Set the Channel A Input to X1 attenuation (XI0 ATI'N LED OFF) and 50R input impedance.
c. Measure the ac voltage at the cathode of CR29 where the amplitude should be approximately 700 mil-
livolts p-p.
d. When the Counter is switched to the XI0 attenuation setting (AUTO TRIG must be OFF in order to
switch to XI0 mode), the amplitude should drop to at least one-tenth the original value, i.e., less than
or equal to 70 millivolts p-p.
8-316. If the Attenuation function is defective:
a. Check the relay control voltage at pin 6 of relay K1 (or anode of CR25). As before, the status of the
relay control voltages indicates whether the relay or the driver is at fault. The voltage should switch
from a TTL HIGH level in the X10 attenuation mode to a TTL LOW level in the
X1
attenuation
mode.
b. The resistors that determine the attenuation value should be checked for incorrect values, opens
,
or
shorts. Note that resistors R108, 109, 110, and 95 are included in both X1 and X10 attenuation paths.
HP 5334B
-
Service Manual
8-43