Soundcraft FX16ii Mixing Console

[thunderfm]

Hi!

I'm trying to repair a Soundcraft FX16ii mixing console and having some difficulties. I'm hoping someone can help!

The problem is with the summing busses. Any signals aren't making it to the outputs. Main Mix, Subgroup, Auxes. The signal is present at the Main insert and Master fader, but doesn't go any further than that.

All the PSU voltages seem fine and I've traced the signal through to each of the ICs for these buses and the issue seems to be the +ve supply for each IC from IC1-IC10, denoted on the schematic as +VA.

My problem is I can't for the life of me find out where this supply is being fed from. There don't seem to be any other references to it on the schematic. Could someone have a quick look and point me in the right direction? The ICs can be found on pages 15-16 on the attached PDF.

Thanks!

[themadhippy]

silly question,but you havnt got solo in place selected by any chance?

[thunderfm]

Not a silly question, but no, I haven't got any solo/pfl or the 2-Track to Mix button engaged.

[magic]

On the first few pages I see a bunch of the ICs you named connected to the unregulated ±17V rails through 10Ω resistors.

[thunderfm]

That's what I saw too. Those rails seem fine as well as the resistors, however after probing it, V+ and V- only seem to be powering IC15 on that block. The others seem to be getting their power from +VA and I'm at a loss as to where that rail is coming from. Unless I'm reading this wrong and that isn't showing a +/- VA rail?

[themadhippy]

To me it looks like its just the name of  the rails,it sourced from the 10 ohm resistors.

[cvanc]

V+ is your source for +VA, travelling thru R26 and filtered by C14.  It then powers IC1 thru IC6 as your drawing shows, and continues on to other ICs (not shown on your drawing) to power them as well.

Test:  While running and in the failure mode, measure the DC voltage across R26 and then measure across R56.  These 2 readings should be roughly the same but I bet you will find a big difference.

Good luck with your repair.

[thunderfm]

Thanks,

Correct. R56 is reading 0.9V drop and R26 is reading -0.24V. The components are reading the correct values, around 10.2R. They were a bit iffy when I first received it, so I've replaced them already. Do you suspect they could be the issue? The caps are also testing fine, both in terms of capacitance and ESR.

[thunderfm]

Update: I found the issue! It appears that the bus IC +vcc rail goes to IC1, 2, 4, and 5, then branches from the leg of C14 and splits off down to IC3 and 6, and up to IC7, 8, 9, and 10. I had to suck out the master faders to see where all the tracks were going, which revealed that the pad for the leg of C14 had cracked and peeled away from the board. So I repaired the pad and hey presto, it's all come back to life.

Thanks all for your help!