SB-303 Hum

[John Q. Doe]

In the standby mode I have seem several SB-303 receivers that
all you can hear is hum. Once in the receive mode the receive
audio is the dominant source of audio. If you wear headphones it
is much more noticeable.

If the HUM is really blasting through and overwhelming the audio,
then look closely at your power supply. I don't have the schematic
in front of me but I seem to remember three different supplies in
the 303. Given the age of the receiver it would not be surprising
if the electrolytic caps in the supply have dried up. Look around
on the power supply board for visible evidence of white powder on
the plus leads of the electrolytics. Also measure your supply
voltages. They should be within 5% of nominal. The power supply
board can be removed for inspection.

DO YOU HAVE THE EXTENDER BOARD FOR TROUBLESHOOTING? If not this
can be a real dog to repair.

73 Chuck WD4HXG

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