soundcraft spirit m4 mixer troubleshooting

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

Yes khron,
to inject just past the bad point, so I can look for further trouble while I wait for the pieces to arrive... do you think that's a bad idea?

I allready put a little pot at the tracer, i'l just do the same on the injecter...

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

just a blocking cap should do it .
you really need to have control over the level . something with a vol control .

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

For signal injection, (in)to where? Right after the point the signal gets lost, or..?

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

yes, it is. I am blissfull.
It's like a new dimension opening before my eyes! Now I got to a point where the signal goes bad, and further on I just can't keep tracking.

Is it the time to build a cable for signal injection? Is it as simple as picking up a jack and shoving a blocking cap and some resistors in between like the tracer?

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Sounds like progress

I recall 3-4 years ago, buying a Soundcraft FX16-II that had gotten something spilled on it (i might be wrong, but i do recall i bought it as faulty). Actually yeah it did, i'm starting to remember having to "patch up" some power traces going to opamps, that had been corroded by whatever it had "drank". I might've had to replace an opamp or two as well, but it's been a long time

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

hey, I took those resistors, but out of circuit they seem ok.. they are r592, r593 and their couples at the "P/B replaces mix"(master A page)

I also got a weird resistance reading at the resistors after the pan pots at mono at mono channels (i'm sticking to those for now), but just like the ones before mentioned, I believe the circuit is fooling me, since they all have the same readings...

Signal vanishes around the Opamps, they have power, but not much sound after r457(mono input cannel 1).. dunno if it is because of it's value or what.. tomorrow I'l tackle it again.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

well done keep searching ..

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

hi there I'm back,
It's too late to look for a stain, I've had it for so long sitting on the shelf, when I picked it up again I gave it a little brush. That was before knowing it got wet. But it was a good idea, thanks, I'm taking a note for the future.

Now, I had the signal tracer that was linked at the beginning, but I had to make a new one with a little potentiometer because the only battery amp I have right now is one of those eggy mp3 speakers, with no volume control and only one miniUSB input. Done.

So now i'm starting to test it, and for a first check I tried eq's and gain pots. And it sounds! ^^

Following the scheme I managed to find a couple of bad resistors for now, but I don't think that's the major trouble... I'll grab a cup of strong tea and get on it.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

see if you can find the stain where the water got in ..it might be a clue

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

yes it's late...
I have the signal tracer still unused, tomorrow i'l check out what it does.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

i dont have the brain power right now to start working out why someone did all that to it . best guess is grounding problems .
i think its best to narrow it down into sections starting from power supply then input boards .
you need a signal tracer or scope really ..

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

ok, on one side I'm missing:

LK58
Resistors: 37,62,223,224,334,335,364,378,397,455,475 and 666
Capacitors: 228,258,261,273 and 317.

And on the other I have this extra:
A link from R547/C313/TR15 to pins 5/6 of CN8.
An other from C315 to gnd, (the screw beside CN8)

Then CN9 pin 2, is sent along a wire through the back of the board to the next board, to a point where it should join R79/R80 to gnd, but the line that goes to gnd is cut off.

On the same CN9 pins 5,6 also go through the back of the board, to c11/c18, the line going to gnd is cut off aswell.
These 3 pins are gnd so they are all shorted together.

4 links at what appears to be return gains,
R258 to R177,
R257 to R183,
R264 to 189,
R265 to R195.

And the last is a wire that goes from the second screw at the top of the top board, trhough a 75ohm resistor to ring in L monitor out and another 75ohm resitor to ring in R monitor output.

That's all I could work out for now. I don't know Who did this and why, I'll try and find out. But it seemed to work fine untill it got wet at a party. Or so I've been told.

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

I'm back, and it appears now the peak lights aren't staying on :S I've tried a couple outputs and it aint fine though.

Ok agent, I'll do that after dinner, my turn to cook today, I'll make a little diagram of what links where and also I'll write down all the wee resistors and caps missing, and we'll see from there.

[Agent24]

Re: soundcraft spirit m4 mixer troubleshooting

I think what needs to be done is a check on the schematic and find where these wires have been connected and try to find why.

They could be to replace blown tracks, part of a legitimate conversion/mod, or some bad attempt to workaround a problem they couldn't fix.

The fault you're seeing now may be related to the original fault if these wires are indeed some repair attempt.

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

ok, re-connected the resistors, and now the 4 return peak leds light up :S

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

Okay lads, I woke up early to do the homework before i get to work, here are the links to the pictures.


back side overlook


Link part(wire added thinking it had tipped off, and re-disconnected when I saw the next parts)


resistors missing beside cn6


wires to ground from r547


back side closeup, resistors wired to ground(extended to the screw beside JK9)


I also realized the two resistors on the last pic, were split in between them, where they join the green wire. I'll replace those and see, before I re join LK58.
With this done, I will be back at noon

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

i must sleep too ..yes some pics will help here ..the schematics are presuming the unit is in the same place as i am ...

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

It's way past my bedtime, I'm not seeing right and starting to mess things up. I'm going to bed, tomorrow evening, with time, I'll make a few pics, try to upload them, and explain you what I have here.

Because as I was taking the board appart to solder that link i had a closer look at the board from behind and I saw that it didn't go to gnd, but to a resistor that isn't there, and a few other odd things.

see you tomorrow

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

skimming through the manual it appears these grounds are floating and not connected to the chassis .

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

am thinking someone was trying to tame ground hum .. so long as something is connected between the grounds it should at least produce sound