Input Amplifier Troubleshooting - HP 5334B Service Manual

8-305. The ac outputs from the transformer can be measured at connector AlJ201. They should be measured
only in reference to ground (Yellow secondary winding, pin 4). MEASURE ACROSS THE TRANSFORMER
WINDINGS. The voltages shown below should be seen when measuring with an oscilloscope set for a ac input,
using a 10:l probe. Transformer (AlTl) Output Windings measured to ground AH201 pin 4 (Yellow wire):
Blue measured to ground
=
20V p-p
Red measured to ground
=
20V p-p
8-306. INPUT AMPLIFIER TROUBLESHOOTING
8-307. Some possible failures in the Input Amplifier are described in the following paragraphs. Note that there
are no Failure Messages which apply to this block. A digital voltmeter should be used for all the dc voltage
checks, and an oscilloscope with a high impedance, low capacitance, 10:l divider probe should be used for all
the ac signal tracing. A variable signal source, such as the HP 3325A Function Generator or its equivalent, can
be used to provide the input signals to the Counter.
8-308. Should the instrument fail while the measurement mode with the display showing only dashes, it may
indicate that the Input Amplifier is not passing the input signal to the MRC. Check for an ECL signal of ap-
proximately 0.8V p-p on a dc level of
+
3V at the appropriate MRC input (U20, pin 30 for Channel A or U20,
pin 28 for Channel B). If the signal is incorrect or missing, troubleshoot the input amplifier.
8-309. This troubleshooting sequence will cover only the Channel A circuit down to the component level since
the Channel B circuit is similar.
8-310. Beginning at the input, the possible failures in the signal conditioning stage include sticky relays, defec-
tive relay drivers, and burnt-out input impedance resistors.
8-311. To check the acldc coupling:
Settings of HP 5334B Under Test
Setting of Signal Source
FREQ A
...........................................
ON
100 kHz, 1V p-p, Sine Wave
(set HP 3325A AMPTD to .5V to generate a 1V p-p signal)
Son
....................................................
OFF 1
volt, dc offset
AC Coupling
................................
OFF
a. Connect input signal to Channel
A
Input.
b. Measure the ac signal at pin 14 (or the junction of C95 and C87) of the coupling selector relay
K5.
It
should be equal to the input signal.
c. While monitoring pin 14, set the Counter to AC coupling (LED ON). The observed signal should
now have no dc offset.
HP 5334B
-
Service Manual
8-42