Soundcraft Spirit FX16 Problem

[Nordo]

I have bought a second hand Soundcraft Spirit FX15 mixer.
Everything seems OK except with the RCA Input sockets (2 Trk Returns) - only one appears to be working.
I want to use it for background music between sets.
I can easily feed both channels from the source (CD player or MP3 player) into the one working input.
However I can't work out how to route that single channel into the L and R of the Mix.

Am I missing something?

I've pulled the back off and there is continuity from the plugs (and my input leads) onto the circuit board, but I don't have the ability to take it any further. All the rear plugs and sockets (with the rear cover) are mounted to the board which makes it a mammoth job to investigate any further.

If all else fails, I could probably sacrifice a couple of input channels, but it would be nice to use the RCA inputs because that's what they are for.

Any help would be appreciated.

[Jazz P Bass]

Schematic can be had here: Index of /ciasteczkowypotwor/SM scena/Soundcraft/Soundcraft-Spirit16 mix

[km6xz]

The 2-Track in circuit is pretty simple since it is working with a line input level the same as as the internal nominal level of the post premp sections, -10dbv. So the whole input is one IC IC15 as its only active device. There is a dual gang level control VR15 to check. If you have no test equipment there are still a few simple tests to pin-point the cause of the problem. Set it normally and feed both 2-Track in, and monitor as normal and short pin 2 and 5 of the VR15 dual pot or pins 3 and 5 shorted together of IC 15. That will tell you if the problem is before the amplifier IC15 or after. If that does not return signal to both outputs, remove the short and use a 100 ohm(or any value from 50-500 ohms) resistor between pin 1 and 7 of IC15. If the signal returns, it is the IC15. If not, the problem is later in the circuit such as the coupling capacitors C87 and C88. Shorting those between each other's + pin will tell if the capacitor is bad if the signal returns. If it is still dead on that defective channel, it is probably the 2-Track switch or 2-trk Return to Mix switch if you have been monitoring the mains 2-buss during these tests. Luckily it is the simplest circuit in the mixer so should be easy to track down, Odds are highest that the IC15 is the bad guy. Unless you are good desoldering, have someone replace the IC for you since unsoldering the 8 pins could damage the circuit board if not done with care. Soldering in a new one is easier.

[Nordo]

The 2-Track in circuit is pretty simple since it is working with a line input level the same as as the internal nominal level of the post premp sections, -10dbv. So the whole input is one IC IC15 as its only active device. There is a dual gang level control VR15 to check. If you have no test equipment there are still a few simple tests to pin-point the cause of the problem. Set it normally and feed both 2-Track in, and monitor as normal and short pin 2 and 5 of the VR15 dual pot or pins 3 and 5 shorted together of IC 15. That will tell you if the problem is before the amplifier IC15 or after. If that does not return signal to both outputs, remove the short and use a 100 ohm(or any value from 50-500 ohms) resistor between pin 1 and 7 of IC15. If the signal returns, it is the IC15. If not, the problem is later in the circuit such as the coupling capacitors C87 and C88. Shorting those between each other's + pin will tell if the capacitor is bad if the signal returns. If it is still dead on that defective channel, it is probably the 2-Track switch or 2-trk Return to Mix switch if you have been monitoring the mains 2-buss during these tests. Luckily it is the simplest circuit in the mixer so should be easy to track down, Odds are highest that the IC15 is the bad guy. Unless you are good desoldering, have someone replace the IC for you since unsoldering the 8 pins could damage the circuit board if not done with care. Soldering in a new one is easier.

WOW!!!!!
The perfect answer. - almost.
I still have a couple of problems.

1. Where is IC15? All the components on the circuit board carrying all the rear sockets are mounted between the board and the rear coverplate. All the screws, nuts etc for all the sockets would have to be removed to gain access to it's components. If IC15 is mounted on this board, it would be a PITA to get access.

2. I have downloaded the circuit diagrams, but they don't list the ICs i.e. what is IC15?

3. I'm only average at soldering. However I do have a friendly TV technician who might be willing to replace the IC.
If I give him your procedure, it might be easier for him to trace the problem too.

Thanks for the great help.
And BTW, you definitely look younger than me.

[Jazz P Bass]

I have downloaded the circuit diagrams, but they don't list the ICs i.e. what is IC15?

IC15 is part# TL072.
It is a common 8 pin opaamp.

Soundcraft Spirit FX16_IC15.pdf

[km6xz]

Hi Nordo, first off, I am surely older than you or dirt....
Second, it is a PITA but true that most smaller mixers use one main pc board parallel with the panel so all the knobs, jack nuts and screws holding XLR and RCA jacks in place, have to come off. Most of the labor costs of repairing small mixers is devoted to the disassembly and reassembly, not diagnostics or actual repair. You do need to get access to the other side of the board. Take a color photo with a smarthome before disassembly so when you go to reassemble it all the knob colors can be easily seen.
Screw lengths are important so self-tapping screws of different length should only go back into positions that had the same length screw before disassembly. An easy way to keep the parts sorted out is to use something with compartment such as an egg carton and put screws into different bins of the carton as you take screws out. The first layer of screws taken off go into bin 1, and the next layer's screws go into #2 and so on until done. Retracing your steps on reassembly is easy if you start using the very last bins first, and finish up by using the last bin.
Good luck

[Nordo]

Thanks for all the help.
You've definitely given me the inspiration to at least do the labour part myself (I've always been pretty good at taking note of how I disassemble something, but most jobs only include 10 - 20 screws or nuts, etc.).

And thanks to Jazz P Bass for the IC info.
I went to the link you gave me and downloaded everything, but didn't realise that one of the PDFs was a multi-page PDF with all the circuits and values.

[g1]

Yes, this one from the link has the full schematics:
http://bee.mif.pg.gda.pl/ciasteczkow...16-2%20mix.pdf

[Nordo]

Yes, this one from the link has the full schematics:
http://bee.mif.pg.gda.pl/ciasteczkow...16-2%20mix.pdf

I downloaded that one.
But I didn't realise that it was multi-page. I just saw the front page, which didn't show a lot, and thought that was it.
I've gone back and found that it had everything I needed (except a brain ).