soundcraft spirit m4 mixer troubleshooting

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

I don't suppose you've considered snapping a photo of the power supply, have you? At least of the area this burnt resistor's from?

And if this is toasted, odds are whatever's connected to it might not be in the best of health either, so... It would be a risky potential-waste-of-time to replace this resistor and have it burn up again, y'know?

[spiros]

Re: soundcraft spirit m4 mixer troubleshooting

Hi,
I have the soundcraft M4 mixer
https://ibb.co/ncxb50
, but the referred schematic does not seem to apply for mine.
By reading the names of the resistors for the power supply board, i cannot trace the components of my board.
and it is a burnt resistor https://ibb.co/jP4Ok0
that i would like to identify in order to replace it.
It is R45.
Would it maybe be possible for someone to tell me the value of it?

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

oops my bad that was VDC

[Agent24]

Re: soundcraft spirit m4 mixer troubleshooting

Carbon is conductive. Maybe the reason the resistance went down is that you are now measuring the original 10 ohms resistance in parallel with the burnt paint etc which will cause an overall lower resistance.

Opamps are running from AC? That doesn't seem right.

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

and about resistors fail high, the devil resistor 666 was 10 ohm, and half burned is now 7,5 ohms out of circuit.. I am changing it though when i get home, plus a few more. And the opamps.

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

well... the resistor was bad, it split in half when I unsoldered it. I found an other hat looks just the same, put it in, and what do you know! I now have monitor outputs!

But phones are still quite fizzy, i probed around that section the opamps ic22 & ic23 and nothing. voltages at V+ and V- were around 13.5Vdc -14.1Vdc, so they are being powered, but it appears ic23 has a negative voltage leak of -13v into it's b-side and that's what's still messing things up (I hope so, tested voltages at other ics and this is the only one that does that)

good night.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

resistors fail high so i guess you measured in circuit ? unsolder one leg for proper testing .

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

tadaaa and finally I got to r266, that is reading 6kohms, when it should be 10ohms. the one beside it r267 has been replaced, and they are both the V_MASTB_L.
I imagine that may buy me monitor outs, but I reckon phones will still have something funny in them.

won't be back to civilization till sunday ev. so I can't do much more now appart from looking for more bad resistors or whatever my dmm can tell me.
wish me luck.

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

good one, I'll add that to my workflow.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

ok so you managed to short it out ...i always put something like cardboard under loose boards when testing and connect any grounds with jumper leads .

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

and you see, the resistor 666, burned up this time I turned the mixer on, while the board was unscrewed to the chassy lying on top of it. I had been looking at the back of it, and left it in such a way that the grounds mounts were in contact with the contacts at the back of the board. Hence, there we have our short. To avoid it happening again I just have to have it well screwed in place with at least 2 or 3 screws before plugging in.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

can you post a pic of the actual pot ?

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

page 11 monitor & phone sections

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

on the resistor note you need to find out what is shorting ... replacing resistors is like replacing fuses . they will keep on blowing until the short is found and rectified .
finding the short may take some time .or you might get lucky and find it quickly .

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

some pots have fixed taps .. in say an audio amp some have a loudness tap . obviously not the case here was just an example .
is the pot in question in the schematics ? if so which page ?

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

well, now I know, thanks

I understand that pots are variable resistors, and that their value is end to end. What I don't understand, is a variable resistor that inside it has a section of non-variable resistors. Shall I assume that a part of those pots has burned out? Or that they are functioning correctly? I can't find the answer online..

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

ok, by petehall's note at page 5 I had not seen, I understand the voltage applied in the equation is the voltage drop.

I looked in the car and there is no speaker so i'm gonna make a little addapter to plug in a minijack from some home speakers, or if I can better, an earphone to trace again, after I find another 10 ohm resistor.. or maybe I just go ahead and test it again, just making sure i don't plug it in again when unscrewed to chassy. It did work, and testing the resistor it told me 7ohms in circuit, gonna check that outacircuit too now..

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

The voltage drop across it ("of course")

In pots, the value is the end-to-end value.

https://en.wikipedia.org/wiki/Potentiometer

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

By voltage set I meant the voltage going through the resistor, 12.4v, and the question was, In the power equation for resistor 666 V stands for voltage(12.4) or voltage drop(0.4)?
I know my questions can sound basic, if I ask is because I can't figure out by miself.

And yes, it is drawn there, but as I said before... I studied carpentry, not electricity. All that drawing tells me is that it has 5pins, and resistance, 10kk. I've been looking at it for a while trying to figure it out, but they are the only ones on the board, and both have some roasty pins(4,5) and both do the exact same, so no other one to compare, and I didn't Know they made pots like that. It just doesn't seem a very smart thing to do, fixing a value for a component like a potentiometer.

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

I still wonder how much power in watts is being drawn at r666, shall I multiply the amperage by the power set, or by the voltage drop?

You know the R, and you've measured the V across it; I = V / R
And then, P = V x I Quite straightforward.

What "power set" do you mean?

And should the variable resistors(vr35/vr87) respond to the turning action at pins 1-2-3?

You have the pinouts of the pots quite clearly indicated on page 11.