HP TM 11-6625-2779-14&P - Manual (Page 48)

Section V Model 3555B
Table 5-7. Function Troubleshooting
DEFECTIVE
FUNCTION VF/Nm CARRIER
75 UNBAL A3K2
135 BAL A1T2, A3K3,
A3R22,A3R23,
A3L1, A3R24
600 BAL A1T2
600 BAL A1T1
900 BAL A1T1, A3K1,
A3R19, A3R20
NG A1R5 thru
A1R8, A1C1,
A1S3
HOLD L1A/B, A1S1
S1
DIAL BAT A1S2, A3R59
a. First determine from the Front Panel
Trouble Analysis chart (Table 5-9) exactly
which range or ranges are defective.
b. Refer to Table 5-9 to determine the
changes that take place when switching
ranges. Select the attenuator pads and/or
gain switching resistors that match your
symptom and check them.
5-36. TROUBLESHOOTING THE INPUT
AMPLIFIER.
a. Check the dc voltages as indicated in
Figure 7-3 to determine if a catastrophic
failure does exist. If the dc voltages are
abnormal (greater than + 10% of the
indicated level), check for open or shorted
components in the area of the abnormal
indication.
b. Check to see that A3K1, A3K2 and A3K3
are operating properly. All relays are de-
energized when either of the 600 BAL
FUNCTION pushbuttons is depressed.
Depress each of the other impedance
functions (900 BAL, 135 BAL and 75
UNBAL) to see that A3K1, A3K3 and A3K2
respectively, energize and de-energize
properly. If any relay fails to operate
properly, check the relay and the
energizing ground supplied through either
pins 1, 2 or 3 on XA1.
5-37. FILTER TROUBLESHOOTING.
a.
First determine that the set is operating in
the TMS input mode. This bypasses the
filters. If the set functions properly in the
TMS mode, check each of the filters by
applying a 1kHz signal at a 0dBm level to
the set. All filters are calibrated for 0dBm
indication on the 3555B meter at a
frequency of 1kHz.
b. Since all the amplifiers in Figure 7-1 are
used in C MSG, the loss of any one will
obviously cause the loss of the C MSG
weighting. However, the bad amplifier can
be isolated by checking the other filters.
Use the following guide to isolate the
trouble to a particular amplifier.
1.
First be sure that the filters have the
correct operating potential applied.
Check the voltage at the junction of
A4R49 and A4C33 to be sure that
there is -20 volts + 1 volt.
2. If none of the filters work, check A3 in
Figure 7-1 (A4Q 11 through A4Q14).
3. If the PROG filter does not work but
the others do, check A6 (A4Q5 and
A4Q6).
4. If C MSG does not work but the others
do, check A1, A4 and A5.
c. After the trouble has been isolated to an
amplifier, check the dc potentials indicated
on the schematic diagram. This will
normally isolate the trouble to a
component. If the dc levels are correct but
the filter response is out of tolerance, no
attempt should be made to change the filter
characteristics. Return the filter to your
nearest -hp- Sales and Service office listed
in the back of this manual.
5-38. TROUBLESHOOTING THE METER
AMPLIFIER AND DETECTOR.
a. Inject a 1kHz, 0dBm signal (.775V rms) into
the 3555B and set the INPUT switch to
TMS TERM, RANGE to 0dBm and the
FUNCTION to VF/Nm, 600 BAL. Measure
the signal at the input of the meter
amplifier (XA3 pin 9). The signal level
should be 6.2mV rms. If not the
malfunction is ahead of the meter amplifier
(refer to troubleshooting tree, Figure 5-8).
5-14