Buster Caps
New Member
Hello! Aspiring amateur audio electronics tech here with great appreciation for and admiration of THIS site. I am happy to discover a truly bountiful resource for those drawn to fixing analog gear problems.
Currently, I have this Yamaha pre amp from the 80's needing attention. Problems include one channel dropping out, static in balance and volume controls, and the power lamp out. AK threads led me to the likely targets: relays, cold solder joints, and servicing controls.
The massive ALPS volume pot was especially resistant, but once removed from the board, I could separate the 'segments' just enough to flood with DeOxit. The relays seemed exceptionally 'touchy'. Probing with a plastic dowel would cause a 1KHz signal observed on my scope to disappear or drop voltage on one channel. I removed 2 relays from the Flat Amp circuits and burnished with 600 wet/dry paper moistened with DeOxit. Suffice it to say that these measures (and some reflowing) made a world of difference. Problems solved -- 90%!?!?
One problem remains. When powering up from cold, the output seems unstable for a few minutes. There is slight but audible volume loss which returns and holds (I guess as circuits "warm up"). I am wondering what could be causing this. What areas/components are suspect?
Also, while I was checking voltages around this pcb, I was puzzled to find voltage in the HEAT SINKs equivalent to that measured in the fastened transistors!!?!? IS THIS NORMAL?
Thanks for any advice.
Currently, I have this Yamaha pre amp from the 80's needing attention. Problems include one channel dropping out, static in balance and volume controls, and the power lamp out. AK threads led me to the likely targets: relays, cold solder joints, and servicing controls.
The massive ALPS volume pot was especially resistant, but once removed from the board, I could separate the 'segments' just enough to flood with DeOxit. The relays seemed exceptionally 'touchy'. Probing with a plastic dowel would cause a 1KHz signal observed on my scope to disappear or drop voltage on one channel. I removed 2 relays from the Flat Amp circuits and burnished with 600 wet/dry paper moistened with DeOxit. Suffice it to say that these measures (and some reflowing) made a world of difference. Problems solved -- 90%!?!?
One problem remains. When powering up from cold, the output seems unstable for a few minutes. There is slight but audible volume loss which returns and holds (I guess as circuits "warm up"). I am wondering what could be causing this. What areas/components are suspect?
Also, while I was checking voltages around this pcb, I was puzzled to find voltage in the HEAT SINKs equivalent to that measured in the fastened transistors!!?!? IS THIS NORMAL?
Thanks for any advice.