Trying to repair a pa20 unpowered mixer for a local charity group. Basic problem is a crackling noise with nothing connected on both Left and Right outputs (shows up on PFL too. I isolated each channel by disconnecting the flat strip main mixing bus, one at at time. Noise still present, so it is not likely coming from a faulty channel. I viewed power supplies for noise on my oscilloscope. +10v supply used on Effects board is very noisy. I replaced all the output side components in the +10v supply circuit ( diode, filtering components, capacitors,resistors, inductor) but see no change. Disconnected the PSU fan just in case it was the source.
note. +/-15v and 48v supplies are noise free.
Questions
- Is this likely to be the source of my noise problem , like I personally suspect?
- If not, what else could I attempt to isolate the noise source?
- Having already replaced all comments in the +10v circuit of the PSU, do you have any suggestions?
Thanks in advance