CR-1020 W/Low FM Hum Between Stations

[JJCalvillo]

Have a slight hum between stations on FM coming from the speakers. Hear it in the open unit but not through the speakers with the other inputs. It isn't loud and you can't hear it once you have a FM station tuned.

Could this be a ground issue?

 

[avionic]

Sounds like a mechanical transformer issue.

Hear it in the open unit but not through the speakers

 

[JJCalvillo]

Sounds like a mechanical transformer issue.

The transformer has some rust on the outside, not horrible but some patches. Is there a cure?

 

[avionic]

Transformer hum is due to loose core laminations or loose mounting fasteners. Is it pretty noticeable with the bonnet on? If not, live with it.

 

[avionic]

You may have two different perceived problems. Likely unrelated.

Have a slight hum between stations on FM coming from the speaker

Do you hear it with the FM muting enabled?

 

[JJCalvillo]

Muchas gracias @avionic . I'm going to set the bias and put the case back on.

Will also tighten the transformer bolts and check the muting, which in this case I believe is something called FM Muting/QTS?

 

[JJCalvillo]

Bias set easily. Transformer wasn't loose, could only turn one bolt slightly.
Does hum with muting on, hum is covered by static with muting off and can't hear it when tuned to a station. Hum increases with volume.

 

[avionic]

QTS?

OTS

OTS (Optimum Tuning System)