Issues with mixer inputs / gain on Studiomaster Session Mix 16-2 Gold Mixer

[velocity kendall]

Hiall,

I have an old Studiomaster Session Mix 16-2 Gold, had it for a long time and i love it, but it's been stored away for a few years and on powering up some of the channels are dead.

When i mean 'dead' i mean that, when i input something to the channel (input slider up full) i'm getting no sound.

But an odd thing happens. When i boost the gain controll knob all the way up for a few seconds, then bring it back down, the channel burst into life and works.

What's happening here?!

I'd love to repair it and get it working again.

Any advice would be great & thanks in advance.

[Audiorepair]

Try exercising the channel ON switches, they are probably dirty/ tarnished.

These have inserts? (Send/Return?) Probably their internal switches are dirty actually.
Spray some switch cleaner into them, and plug a  jack in and out a few times to clean the switch contacts.

If you don't have switch cleaner, just plugging a jack in and out a few times might do it.

[velocity kendall]

Thank's, i'll try that.

I've checked the insert's on all the channels and they all work fine, which is odd . . . . .

[KevinA]

If I remember rightly, these, like the old Powerhouse series, use TL072's in the channel strips.

I had many instances of the Powerhouse series with your symptoms. The TL072 seems to loose its gain, until you blast a signal through it, when it returns to normal for a while. Trace the signal though using a low level input; you should quickly find the culprit(s).

[Audiorepair]

If I remember rightly, these, like the old Powerhouse series, use TL072's in the channel strips.

I had many instances of the Powerhouse series with your symptoms. The TL072 seems to loose its gain, until you blast a signal through it, when it returns to normal for a while. Trace the signal though using a low level input; you should quickly find the culprit(s).

Sorry, but this is complete bollocks.

Op-amps do not behave this way.


What does behave this way is dirty Inserts, and possibly channel switches.

[Audiorepair]

You can inject a signal into the Insert socket to determine whether the fault is upstream or downtream from here, or the socket itself.

[velocity kendall]

Thanks for the feedback.

Tomorrow i'll clean all the inserts with switch cleaner [and the channel on/off switches].

Hopefully this will work.

It's curious though that it's happening with all the inputs bar 2 of them [its a 16 channel mixer], which makes me think that the fault might be elsewhere other than on the strips themselves?

Just a thought though.

[Audiorepair]

If the main left and right outs also have Inserts, (quite likely) or any switches that are dirty, these will affect all the channels.
You should clean these first.

[velocity kendall]

Thanks Audiorepair.

I've started working on another mixer now, but i'll get back to it (short attention span!)

Cheers.