Soundcraft Gigrac trouble shooting

[pstrick]

Does anyone in the forum have experience with the Gigrac 1000? Recently lost the right channel, found a bad opamp. Upon repair, the channel now has a significant amount of noise that was determined to be coming from the power supply. The left channel is still clean. Any thoughts?

[Jazz P Bass]

Gigrac schematic

Here is a link to previous post that includes the schematic.
Best that I can do.
Link:http://music-electronics-forum.com/t10822/

[Enzo]

If the same power supply powers both channels, how can the noise be from the power supply?

[pstrick]

That is my question... I am not an EE, but an EE friend who found and fixed the bad opamp, attemped to determine the cause of the noise. This powered mixer has all of its mixer circuit mounted to a faceplate. It turns out that the noise can be eliminated by moving the faceplate relative to the power supply (further away, rotated). So he suspects that something in the channel is susceptible to radiated EMI, while the other channel is immune. I'm not sure this makes sense.

[Enzo]

Or a broken shield on the input cable to that channel power amp... or something...

[russhulme]

My best advice would be to, unfortunately, get rid of it. I bought 3 of these units. I took 2 to an island in the Caribbean. First one was DOA, second one started cutting in and out after 16 gigs. The third one died back in the states and sent it to Soundcraft. Cost me 200 bucks to repair. I'm not hard on this stuff, very careful. The thing is, Soundcraft knows they are putting out an inferior product (their service notes tells of out of tolerance Chinese resistors. You can email their service and get the schematics and notes. Good luck.

[Alex R]

...seen two of these with bad power supplies. Switch mode. Beyond my expertise to fix at component-level. New board very expensive. I don't think my heart is going to lift when the next one comes in!