Astron Power Supply - Astron RS-35M power supply

Astron Power Supply -  Astron RS-35M power supply

Power Supply Hum - a hum after it has been running for a while....

I have an Astron RS-35M power supply that supplies the correct voltage to my equipment but has a hum after it has been running for a while. Would the problem be in the transformer and how would I test it? I have not had the cover off yet.

Answer

• Most likely electrolytics breaking down after heat builds up
• It only takes one leaky cap to cause a 120hz hum. The 120hz ripple is already present on the output of the rectifier
• That might be loose laminations in the transformer core.
• Bad transformer, not that uncommon.
• Weak capacitors is a common cause of hum in these supplies

Is the hum coming from the speaker in some radio equipment or from the power supply? If its making a hum in the speaker its probably a bad diode in the bridge rectifier and not the electrolytic caps since you would have to loose most of the capacitance to cause a hum at low current like a radio in receive mode. If there was no hum in the speaker of a transceiver during receive but hum on transmit during high current draw then it could be electrolytic caps going bad.

If the hum is coming from the power supply it could be from the transformer mounting bolts being loose or from something else being loose (case screws?) in close proximity of the transformer. Worst case would be the transformer not being properly dipped in varnish and placed in a vacuum chamber to get the varnish pulled between all the laminations during manufacture and the laminations are buzzing, That's hard to fix without taking out the transformer and running it through the right process.


https://forums.radioreference.com/electronics/313262-power-supply-hum.html

http://forums.qrz.com/archive/index.php/t-57472.html

http://www.repeater-builder.com/astron/astron-intro-stuff.html