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Volume11
New member
Hi guys, I’ve been a long time lurker, but I’ve finally run into an issue that I may need some assistance on, so I decided to register and reach out. I’m working on a 388 that I picked up about a month ago. I managed to get the tape deck going with several fixes, including some damaged pcb traces that needed some attention.
Now I’ve moved on to the mixer side, where I’ve cleaned all of the pots and molex connectors. The only issue I’m having so far, is this nasty high pitched hum. It occurs without any of the channels engaged, and reacts strangely to the master fader. I believe that I have narrowed it down to the Aux/Effects section of the mixer, just based on the fact that when I disconnect P123 on the Monitor PCB, the sound stops. If this isn’t the case, than the main XLR outputs must be tied to the PCB as well, but I’m not seeing that in the schematic.
Has anyone dealt with a similar issue with this machine? The voltages on the power supply seem to checkout ok. I replaced the filter caps in the power supply. I also tried some different TL072 chips on the monitor board, thinking that I may have had a bad one.
Thanks in advance for any help.
Now I’ve moved on to the mixer side, where I’ve cleaned all of the pots and molex connectors. The only issue I’m having so far, is this nasty high pitched hum. It occurs without any of the channels engaged, and reacts strangely to the master fader. I believe that I have narrowed it down to the Aux/Effects section of the mixer, just based on the fact that when I disconnect P123 on the Monitor PCB, the sound stops. If this isn’t the case, than the main XLR outputs must be tied to the PCB as well, but I’m not seeing that in the schematic.
Has anyone dealt with a similar issue with this machine? The voltages on the power supply seem to checkout ok. I replaced the filter caps in the power supply. I also tried some different TL072 chips on the monitor board, thinking that I may have had a bad one.
Thanks in advance for any help.
