alesis qs6.1 ac hum

[skip2011]

I got an alesis key board in for repair with a bad ac hum (60 cycle). I found q6 and q7shorted and replaced them. The hum got much better but is still present and noticeable. These transistors were on the -5 v. I have seen regulators cause problems in the past, But I also have an op-amp in the same circuit as the two transistors. I don't want to just throw parts at this thing so I thought I would put this out. Has anyone had this or a similar problem and if so, what was the cure?
thanks in advance, skip2011

[The Dude]

Do you have a schematic you can share? I've no idea what q6 and q7 are without a bit more info. Sans that, I would scope (if you have one) or check the supplies with a dvm and see if any of the supplies have excessive AC on them.

[skip2011]

Unfortunately, I don't. The circuit is fairly simple and the transistors are associated with the line out. N channel j-fets. AC ripple is app 4.6 mil. the regulator is a 7905 and the -5v is reading4.12 volts.

[Jazz P Bass]

Is the hum only on the line out?

Something is loading down the -5 Vdc rail.
Is the regulator getting hot?
Is there a Vac component on any of the power rails?

[doctor]

Transistors Q6 and Q7 (J111) are used for muting and have no relation to the hum.

Firstly check supply voltages (+15V at U7:8 and -15V at U7:4) and, if them are ok, check whether there is DC voltage at the outputs of the U7 (U7:1 and U7:7). If a DC voltage presents, replace this opamp (NJM4580).