HP 654A - 5-84. Troubleshooting the Buffer Amplifier; 5-86. Troubleshooting the Balanced Amplifier; 5-88. Trouble Isolation in the Remainder of the Leveling Loop

Model 654A
Section V
Table 5-5. Front Panel Troubleshooting ( See Paragraph 5-74)
MONITOR t
POINT INDICATIONS
MOST LIKELY TROUBLE AREAS
ACTION REQUIRED
ABC
ABC
ABC
AC
AB
OTHER
TROUBLES
Incorrect
flatness or
level
No output only
at certain
frequencies
Incorrect
frequency
Oscillator circuit or Power Supplies
Multiple troubles
1) Counter Emitter Follower
2) Meter circuits Average Detector
Multiple troubles
1) Counter Emitter Follower
2) Attenuators ( S4) and/or
Impedance switch ( A4)
Counter Emitter Follower
ALC Loop - consisting of Buffer and
Balanced Amplifiers, Average
Detector and ALC circuits
Metering circuits ( and Average
Detector)
Attenuators ( S4) and/or Impedance
Switch ( A4)
Go to0on troubleshooting tree.
1) Troubleshoot
2) Go tosOon troubleshooting tree.
1) Troubleshoot
2) Check all positions of
attenuators and impedance switch.
Troubleshoot.
Go to on troubleshooting tree.
Go tolOon troubleshooting tree.
Check all positions of attenuator
and impedance switch.
ALC Loop - consisting of Buffer and
Balanced Amplifiers, Average
Detector and ALC circuits
Oscillator calibration
Oscillator calibration
Go toOon troubleshooting tree.
Calibrate
Calibrate
t COUNTER OUTPUT
654A meter indication
Front panel output
connectors
A = 0.1V rms into 50 ohms;
B = + 1dBm or greater;
C = approximately 0.8V rms
into 50 ohms;
A = intermittent or no signal
r3 -= less than + 1dBm
C = intermittent or no signal
0 Check the dc voltage at the collector of A2Q25
which should be from + 6 to + 8 volts.
Troubleshoot the Balanced Amplifier, A2Q11
through A2Q23 and associated components. If in
step O the dc voltages were incorrect and were
equal and opposite then the problem is probably
in the differential amplifiers A2Q11 through
A2Q16. If the dc voltages are incorrect but of the
same polarity then the problem is probably in the
feedback amplifier A2Q22, A2Q23 and A2Q17.
If the output signal is not present on A4 Pin 3 and
(in the BAL modes of the IMPEDANCE switch)
A4 Pin 4 then check the resistive networks on the
A4 board. If it is present, check the cables to the
output connectors J3 and J4.
5-21