Model 8340A - service
Open Loop Test
The following is an open-loop test that can be used to
troubleshoot the A49 YO Loop Phase Detector. Set the instrument
to CW mode. Disconnect the cables at A49Jl and A49J2, and measure
the YO TUNE voltage at A49J2. The voltage will be either -6.9 v,
corresponding to case Number 2 above (lag), or else +6.9
v
corresponding to case Number 3 (lead). The bias voltages of Q3
ihould be close to those listed in Table BD-2. Switch the sampler
IF and the 20-30 MHz input cables (A49J3 and A49J4). This should
reverse the polarity of YO TUNE. The corresponding bias voltages
for Q3 can now be verified. If the bias voltages of Q3 are
correct for both cases but the polarity of YO TUNE does not
reverse, then troubleshoot the Loop Integrators, Block
F,
and the
sample and Hold, Block
H.
sample and Bold
With HLEY (High Lock Enable Yig Oscillator) HIGH, and LLEY LOW
(CW or MANUAL mode), the output of the Sample-and-Hold, Block
H,
should track the input. verify that HLEY is HIGH and LLEY is LOW,
then measure the input and output of U3; they should be
identical.
FM
Coil Driver
If the FM Coil Driver, Block
I,
is malfunctioning, the YO Loop
will acquire phase-lock, but the residual FM on the YO Output
will be far greater than the typical specification of 60 Hz. The
de output of the op-amp should be
O
v.
·
Logic Inverter/Translator
To test the Logic Inverter/Translator, TP3 (HLEY) on the A50 YO
Loop Interconnect assembly can be used to force a logic condition
to occur. Connect HLEY to +5V and then to ground, verify that the
outputs are within the given limits. LLEY can be measured at U3
pin 14; YO Loop Disable can be measured at UB pin 5.
HLEY
LLEY'
YO LOOP DISABLE
+sv
2.4 to 5.0V
-0. 5 to -1. OV
ov
0.0 to 0.5V
-2.0 to -5.0V
SE.RIAL PREFIX 2344A
8-328b
Scans by HB9HCA and HB9FSX
Содержание 8340A
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