Symmetricom 5071A, Assembly And Service Manual

Page: 136 / 202

2. Service
Assembly/Module Diagnostic Trees (Diagnostic Section 3)
120
A19 Diagnostic Tree
(A/M Subsection 9)
This subsection describes the diagnostic tree for the A19 module and
associated circuits on A6. The A19 module is an ovenized voltage-controlled,
quartz-crystal oscillator (VCXO), it receives oven and oscillator power from
the A6 module. At power-up, the VCXO requires a warm-up time of at least
10 minutes before its output is stable.
The 10 MHz VCXO output is tuned over a nominal range of
±
3 Hz by an
electronic frequency control (EFC) voltage. The EFC signal is generated by a
DAC on A6.
3.9.1.1 A6 Unloaded A19-Power-Supply Voltages
1 Power down the instrument and remove A6.
2 Check the continuity of fuses A6- F3, F4, F5, (2.5
Ω
or less) and replace as
required.
3 Mount A6 in the instrument with the short extender card
(05071-60051).
4 Disconnect A19 from A1 at A1J11 and CBT cable from A2J2.
5 Disconnect the semi-rigid cable from A19 to A9J5.
6 Connect the signal generator output (set to provide 10 MHz at
+7 dBm) to A9J5.
7 Apply power to the instrument. (Wait until LCD displays
Fatal Error
.)
8 Measure A19 supply voltages with a DMM at test points TP9, TP8 and TP7
on A6. Voltages should be as follows:
TP9, (+12 V nominal), more than 11.75 and less than 12.75 volts.
TP8, (-12 V nominal), more than -12.75 and less than -11.75 volts.
TP7, (+10.8 V nominal), more than 10.3 and less than 11.3 volts.
QUESTION: Are the power supply voltages correct?
If Yes: Go to, 3.9.1.2.
If No: Remove power, replace A6, and retest.