Hello,
Thanks, I replaced all the electrolytic caps on the filter board: C3, C10 and C4. Now I only have a loud pop when switching between FLAT postion and Max. Loudness position, switching between Max. Loudness and Speech no or external speeker no pop sound. Checked for DC, there 0 voltage on all the 2 outputs of the filter board: #2 is for the Max. Loudness correction and #3 is for the FLAT correction.
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If I leave the amplifier for 2 min, the POP sound goes away gradually until no pop is heared.