[Test-Equipment] HP 8640B audio oscillator thermisto

[Craig C. Heaton]

I have a commercial version HP 8640B with options 001,002,003. It can no
longer produce a sine wave from the audio oscillator. I'm down to thinking
the thermistor part # 5080-1718 is the root cause. Looking the schematic the
epoxy encapsulated device contains three thermistors. There are three leads
coming from the device. All three thermistors are in series; Connection "A"
attaches to a point after the first thermistor. Connection "B" is at one end
of the string of thermistors and Connection "C" at the other end. "A" to "B"
is open, "A" to "C" is about 56 ohms, and "B" to "C" is open. In other
words, the thermistor between points "A" and "B" is kaput.

Anyone have a work around as how to rebuild this item? Or, how about a
working osc. part # 08640 60019?

Thanks
wd8kdg
Craig