TSP #219 – Teardown & Repair of an Agilent 81101A 50MHz 20Vpp Pulse Generator

In this episode Shahriar takes a close look at an Agilent pulse generator which does not produce any output signal. The generator has an output ON/OFF function which can disconnect the unit using a microwave relay. The output spectrum of the faulty unit shows the presence of the desired spectrum and residue of the square wave signal.
The teardown shows that the output relay is not being engaged with the output is enabled. The fault is traced to the relay switch transistor (NPN) which does not respond to the control signal. The replacement NPN corrects the problem and the unit produces the correct output. The unit’s maximum output swing as well as frequency accuracy are verified using a R&S MXO-4 Series & a Rubidium frequency counter.

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