Have a low humming noise from speaker when powering up and thru scanning process of my Bearcat III Scanner and picks up signals ok.Trying to rule out problems before ordering parts (if I still can). Could this be a power transformer going bad ?
Consider remounting the power transformer with insulated rubber mounts. It may be the hum is simply amplified through the chassis.
Yes, it does sound like a bad power transformer. Try powering it using a DC supply or battery and see if the hum goes away.
No it's certainly not a bad transformer, transformers hardly ever fail and when they do, they either go dead completely or smoke. A common cause of hum is a bad filter capacitor in the power supply. If I remember correctly, there are two electrolytic capacitors located on the PCB near the rear panel. Try replacing both of those, they cost only a few dollars and given this thing is 30+ years old they likely need it.
The BCIII does have a 12VDC input using the other two pins of the power connector so you could test it that way to find out, but do make sure you get the polarity right or you'll smoke it.
I have one replaced all that nothing helped was slightly better on 12 volt stand off supply. might be electrolytic capacitors in IF section or one of the two receive boards I still had the hum internal and external ps`s who knows hope this saves You some money and helps .....
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