[sdiy] Mega Madness One

[harry bissell]

Those probably ARE the mix busses...
now if so... they are probably summing junctions
of an inverting opamp (ie virtual ground)

and you should NOT see a voltage there

Now if you looked for current, you'd probably find it
(it is not easy to view current either...)

my guess, anyway...

H^) harry

Michael Ruberto wrote:
> That's my new name for my Tascam MM-1 mixer. Because listening to my 
> 440hz test tone coming out of it for hours on end has driven me mad. 
> The mega part comes from the fact that I cannot trace a single signal 
> ANYWHERE. This is most madening. Each of the 16 channel cards are 
> bussed through a common backplane. The backplane has 16 traces and a 
> big fat ground. Besides power rails and ground I cannot find the 
> merest shimmer of my sine tone on any of these traces even though I 
> hear it coming from the mixers outputs.
>
> Ok maybe it isn't this backplane that carries the stereo bus. There 
> are a pair of wires leading from the PCB marked "Power" to each 
> channel card. No luck with these either. They just carry 5V logic 
> signals for controlling the mute for each channel. Pressing the mute 
> button on a channel makes it's respective logic state change.
>
> On the right side of the mixer are the stereo master channels. The 
> stereo outputs are taken from the left master card. On the bus PCB 
> between these cards I can find my test tone on 2 traces. On one trace 
> it's 1V PP and the other it's about 10mv PP. I guess this is normal 
> because as of yet there has been no intermittent distortion or 
> dropouts since it's been on my testbench. Hmmm I wonder if this 
> problem only occurs while racked....
>
> Well troubleshooting this thing is just impossible without schematics. 
> If can't isolate a ground loop type problem when it's back in the rack 
> I guess I'm in the market for a new mixer. I should probably find a 
> good shrink too.
>
> M. A. Ruberto
>
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