ASTRON RS-35M power supply humming

Try to problem solve with an ASTRON RS-35M power supply humming.

I have noticed an Astron RS-35M a Humming. So I have three 2 models RS-35M and one RS-20 and only one has the hum I think on one ... But the other is never powered on.

ANSWER :

The hum or "buzz" is quite common in power supplies with transformers....the old analog type. 

I've got one that has a constant buzz/ Another supply gets buzzier as you draw more current! 

A friend had one that was rather annoying. He took it back and got another quieter one (returned).    The power transformer tends to resonate on the chassis. 

Hope that explains your problem somewhat!

Often, the mechanical noise you hear from the Astrons is coming from the thin sheet metal cabinet.  When you're hearing the hum, put your hand on the cabinet top and press down lightly.  If the noise is substantially changed or reduced, the problem is that the steel cabinet is being affected by stray flux from the transformer.  One way to fix this is to damp the cabinet - something you'd normally do from the inside, but there's no room in the Astron to do that and the cabinet top can't be simply pulled straight up anyway.  The way it slides would prevent using damping material inside.  You could apply damping foam (adhesive backed) to the top of the cabinet on the outside and that would help a bit.  The foam can be obtained from a number of companies on the web who deal with quieting down noisy PCs.
Another approach might be to take the steel cabinet top to a sheetmetal shop and have them bend an aluminum top for you.  I've had more noise problems with Astrons from this source than from loose transformer laminations or bolts.

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