Dr. Ear
Super Member
I recently completely overhauled my C-70 preamp. I replaced every single electrolytic capacitor (used Muse and Silmic) and the 8 relays, opened and cleaned the tone control and phono input switches and adjusted all the parameters.
While the phono MM input was dead quiet afterwards, the MC input had some static noise. There was a random faint popping and crackling. I was thinking of a defective Zener or transistor first. On closer inspection I noticed some brown stuff around the feet of TR101-104 (picture attached). Those transistors are pairwise covered by a rubber cap for better thermal stability. I desoldered them and found lots of this carbonized glue covering their legs far up to the plastic. I removed the glue, tested the transistors with my Atlas semiconductor tester, found them OK and soldered them back. Now the MC input is perfectly quiet. All C-70 owners should take a closer look to TR101-104 and remove the glue.
While the phono MM input was dead quiet afterwards, the MC input had some static noise. There was a random faint popping and crackling. I was thinking of a defective Zener or transistor first. On closer inspection I noticed some brown stuff around the feet of TR101-104 (picture attached). Those transistors are pairwise covered by a rubber cap for better thermal stability. I desoldered them and found lots of this carbonized glue covering their legs far up to the plastic. I removed the glue, tested the transistors with my Atlas semiconductor tester, found them OK and soldered them back. Now the MC input is perfectly quiet. All C-70 owners should take a closer look to TR101-104 and remove the glue.
