This is what we suspected earlier but couldn't prove. Those capacitors, plus C54, need to be replaced with film capacitors similar to C23, C24, C52 and C53.
73,
John KD6OZH
----- Original Message ----- From: "Juan Rivera" [email protected] To: "John B. Stephensen" [email protected] Cc: [email protected]; "Bill Ress" [email protected]; "Dave Black (Home)" [email protected]; "Dave Black (Work)" [email protected]; "Dave hartzell" [email protected]; "David Smith" [email protected]; "Don Ferguson" [email protected]; "Juan. Rivera (Home)" [email protected]; "Juan.Rivera (Work)" [email protected]; "Samsonoff@Mac. Com" [email protected] Sent: Saturday, July 14, 2007 18:18 UTC Subject: Source of 70 cm Microphoncs Found
John,
The microphonics is caused by C19, C27 and C28 (.047uF 25V) and C50 and C51 (.022uF 25V).
I found the best way to isolate this is to inject a CW signal into the receiver, tune the signal in at the IF output using my TS-2000 in AM mode, and then listen to the audio output while lightly tapping each component one at a time.
According to my research, barium titanate, the base ceramic material for most ceramic SMD capacitors is inherently microphonic.
Juan