HP 85660B A7A2 100 MHz VCXO, Troubleshooting

A7A2 100 MHz VCXO, Troubleshooting

The 100 MHz VCXO supplies all of the fixed reference frequencies for the HP 8566B. Separate 100 MHz outputs are routed to the A6A9, AlOA4, and A7Al assemblies. A 400 MHz signal is applied to the A7A3 assembly. The A7Al assembly divides the 100 MHz input to provide 10 MHz and 20 MHz references.

100 MHz Oscillator @

The tune voltage at A7A2TPl is nominally -8 V. If an unlocked condition exists, this voltage is either -23 V or -1.3 V. If the level is -23 V, check the 10 MHz reference to A7Al. If the level is -1.3 V, check the outputs of the 100 MHz Buffer/Amplifier.

Typical voltage levels for the oscillator transistor Q5 are:

Emitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -12.8V

Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -11.9V

Collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..O.O V

100 MHz Buffer/Amplifier @I

All 100 MHz output levels should be approximately 0 dBm. Typical voltage levels for each transistor are as shown in Table 1.

Table 1. 100 MHz Buffer/Amplifier Voltage Levels

	Q6	Q7	Qll
Emitter	4.0	3.9	3.9
Base	4.7	4.7	4.6
Collector	9.3	9.4	9.4

Quadrupler @ and 400 MHz Amplifier @I

Typical voltage levels for the Quadrupler and 400 MHz Amplifier are as shown in Table 2.

The 400 MHz Amplifier output at A7A2Jl (96 cable) is approximately -10 dBm when the A7A2 100 MHz board assembly is in the casting.

Table 2. Quadrupler and 400 MHz Amplifier Voltage Levels

	Q3	Q4	Ql	Q3
Emitter	-4.6	-5.1	-6.6	-6.6
Base	-5.9	-5.9	-5.9	-5.9
Collector	0.0	0.0	0.0	0.0

2A7A2