Soundcraft Spirit Live 4*2 Service Manual

[GBird]

Running the width of the desk are 4 Mute busses controlled by the mute group buttons on the aux master module. 0V means un-muted, -17V means muted.

 

The can be found on CN2 pins 3-6.

 

If you put a meter on these they should switch between 0V and -17V as you press the mute buss masters.

 

Compare the level of hiss at the insert points for the groups and mains. They should be the same there as along as you have the same number of input channels routed to both groups and mains.

 

Really appreciate your help here Brian, I'll try later on this evening. Trying to learn here as well, is the reason for trying the insert points for the groups and mains to check that the issue is after the insert points for the groups?

[Brian]

The insert points are early on in the path from the mix busses to the finals group and main outputs. The circuitry between the busses and the insert jacks is identical for both group and main so the noise should be the same here. If it is then the noise is coming in later on, if they are different then we need to look elsewhere.

[sunray]

...the fault turned out to be 2 failed ICs.

 

Let me guess...NE55342 or NE5534s?

Of course

[GBird]

The insert points are early on in the path from the mix busses to the finals group and main outputs. The circuitry between the busses and the insert jacks is identical for both group and main so the noise should be the same here. If it is then the noise is coming in later on, if they are different then we need to look elsewhere.

 

Thanks Brian, the hiss on the groups is present on the inserts for each group but not on the main so it must be earlier on.

 

With the mute groups, pins 3-6 on CN2 all measure 0v whether the mute is switched on or off. This doesn't make sense in my head as mutes 2&3 are working so would expect 4&5 to show -17v?

 

In a new strange turn of events, on every channel selecting output to either groups 1&2 or 3&4 is now causing the output to all groups, not just 1&2 or 3&4 respectively. I'll try reseating the ribbons connecting the channels tomorrow as this is the only thing that has changed!

[GBird]

As it turns out, mute group 3 has stopped working as well. Looks like there's no continuity from pins 3, 4 & 5 so will resolder these to hopefully resolve. The hiss is still there and the issue with the group buttons for each channel still persists.