HP 3400A Operating And Service Manual page 27

Section V
CHECK
Measure the de signal at emitter
Reading should be approximately -2 . 35 Vde.
Measure the dc signal at pin 9 (A6).
should be approximately - I . 65 Vdc.
®
Investigate R619. R4. and thermocouples.
Paragraph 5-34 for thermocouple check.
®
Investigate Q606 and associated circuit.
Measure the ac signal at base
to Figure 5-8 for waveform.
5-10
Figure 5-7. Input to Demodulator (feedback loop open)
Table 5-6. Troubleshooting Procedure (Cont'd)
PROCEDURE
of
Q605.
of
Q605.
Figure 5-8. Output of Demodulator (feedback loop open)
POSITIVE SIDE OF C605
Insert +IOmV signal through 499kO
resistor to pin 13 on A6
Sweep
Vertical
DC coupled
use 10:1 probe
PASSES:
FAILS:
Reading PASSES:
FAILS:
See
Refer PASSES:
FAILS:
BASE OF Q605
Insert +10 mV signal through 499 kfl
r'esistor to pin 13 on A6
S weep
Vertical
AC coupled
use 10:1 probe
Model 3400A
5 ms/cm
=
2. 0 V/cm
=
ACTION
® @
Proceed to
Proceed to
G)
Proceed to
®
Proceed to
Proceed to
Proceed to
5 ms/cm
=
0. 2 V /cm
=
01768-2