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Azur Electronics

January 2016

The HP 8657D Signal Generator had a reported fault "Smoking!".

Front view of Signal Generator and Modulator below
This is a complicated beast and luckily the Signal Generator part completed all its User Confidence and Adjustment Tests ok. There is no service information for the Modulator part.
Top view of Modulator with cover removed
In the Modulator the suppression capacitor was replaced. This is for electromagnetic interference suppression across the mains line and failure is a fairly common problem. They are rated at 275Vac which is probably fine in the USA with mains line voltages of 115Vac, in the UK 230Vac is more significant. My local line voltage is 254Vac, right on the upper limit!

SMPS in Modulator
The Computer Products NFS40-7610 Switched Mode Power Supply is drawing excessive mains current and not producing any dc outputs. This is a commercial switched mode power supply made in China and without any service information. The fault was eventually traced to Transformer T2. As replacement custom made parts are not available it means a new power supply is required.

Fortunately these are still available from several suppliers, ie Farnell 1516410 for £39.33 each.

I don't have the facilities to test the Modulator although it powers up ok with another power supply.