HP 606A Operating And Service Manual page 39

Model 606A
Table 4-2. Troubleshooting Chart (Cont'd)
Section IV
Table 4-2 and 4-3
F. MODULATION MONITOR
Most troubles can be found easily by measuring the voltages in the circuit as follows:
Set MODULATION SELECTOR to INT. 1000%
MODULATION AMPLITUDE to
100
%
V9A ( 1/2 12AT7)
pin 2
pin 3
2.8 volts rms
2.8 volts rms
o vdc (approximate voltages)
+3.9 vdc
Diode CR4 ( 1N90) prevents a high negative voltage developing at the cathode of V9A during warmup.
Such a high voltage of reversed polarity would damage electrolytic capacitor C56. The high negative
voltage could also be developed if the heater of V9 burned out or if the instrument were turned on with
V9 removed.
Diode CR5 ( 1N90) is the detector for the modulation meter.
Both diodes can be measured only out of the circuit. Forward resistance should be approximately
500 ohms. Back resistance should be greater than 100K ohms.
G. CRYSTAL CALIBRATOR
Most troubles can be found easily by measuring the voltages in the circuit as follows:
Set CRYSTAL CALIBRATOR to either 100 KC or 1 MC as indicated.
100 KC 1 MC
VIO ( 6AW8A) DC AC
pin 1
pin 2
pin 3
pin 6
pin 7
pin 8
pin 9
o vdc
-58 vdc
+71 vdc
O vdc
-82 vdc
+108 vdc
+240 vdc
0 volt
41 volts
0.44 volt
0 volt
60 volts
31 volts
41 volts
rms
/711S
1711S
rms
2711 S
rms
S
DC AC
o
vdc
-34 vdc
+196 vdc
o
vdc
-35 vdc
+122 vdc
+222 vdc
0 volt rms
23 volts rms
0.1 volt rms
0 volt rms
23 volts rms
7.5 volts rms
22 volts rms
all
voltages
approximate
Table 4-3. Troubleshooting the Feedback Loop
SYMPTOM. No output on all ranges, or R15 ( 100
ohms) burns out on all ranges.
PREPARATION. This procedure assumes that:
a) The - 200 volt and + 300 volt supplies are func-
tioning properly.
b) All heater voltages in the rf chassis measure
the correct value.
c) All tubes have been checked.
d) The oscillator is working properly on all
bands and gives approximate voltages and cur-
rents as listed in table 4-4.
e) The tuning capacitor or its leads are not short
circuited.
PROCEDURE. Unless otherwise noted all mea-
surements are made at 115 volts rms, 60 cycle
line, with the Model 606A on CW.
Proceed from step to step. Rectify any troubles
before proceeding to the next step.
Measurements are made with an
e
Model 410B
VTVM and Model 428A Clip-On Milliammeter,
or other milliammeter.
E = dc voltages; ' e ac voltages; I = current.
Procedure Observe or Measure
1. Disable the feedback by connecting pin 2.
V6 ( 12B4) to - 200 volts by shorting R30
(220K).
This bias should cutoff V6 and provide no current for V3
or V4. There should be no curtent through R15. Check
with
e
Model 428A.
00170-2
4-7