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Old 01-11-2017, 08:18 AM   #101
5inc
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Default Re: soundcraft spirit m4 mixer troubleshooting

if you turn it up it don't do nothing either
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Old 01-11-2017, 08:39 AM   #102
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Default Re: soundcraft spirit m4 mixer troubleshooting

That's not how Ohm's law works - just because a resistor is rated for 0.25W doesn't mean it dissipates that much no matter what

Both the monitor and the phones outputs get their signal from "MIXL/R", as i see on page 11.

If the main outputs work, then at least in theory, you SHOULD have signal on the "MIXL/R" (at R277/278). You can use your signal tracer again, and see where it "ends".
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Old 01-11-2017, 03:36 PM   #103
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Default Re: soundcraft spirit m4 mixer troubleshooting

i'm off at a friend's house, but I took my homework with me, allthough I forgot the speaker home, or in the car, ... if it's there I'll fetch it tomorrow. I also forgot the lightbulb-in-series plug.

In either case, i've only got my multimeter here, and the headphones, plus some basic hand tools and soldering kit, for if I need to build something, which looks like I will.

Yes, I DO have signal on the MIXL/R output, tracking I had a fine sound on the 3d pin.
So now I'm facing trouble from mixL/R forward. Allthough I hope that it gets a bit more exciting than a missing resistor this time :P

Since I only have the multimeter I'll just go ahead and follow the page 11 of the schem looking for bad or missing components/voltages for now since it's narrowed down to that page, and tomorrow I'll see what I can build to use the signal tracer.

Then Khron, if I can't rely on power in the equation my guess is that that resistor will be drawing 0.04amps, so to get the power drawn do we multiply that by the voltage or by the voltage drop?
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Old 01-11-2017, 03:41 PM   #104
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Default Re: soundcraft spirit m4 mixer troubleshooting

Exactly - only use values you can measure, or which you know from the get-go (like resistor values and voltages, in this case). The rest you can figure out, if needed.
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Old 01-11-2017, 04:37 PM   #105
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Default Re: soundcraft spirit m4 mixer troubleshooting

sweet, but I still wonder how much power in watts is being drawn then, shall I multiply the amperage by the power set, or by the voltage drop.

tracking down from the end back I found the pots for headphone and monitor are doing something funny. You see, they have 5 pins, 3 are closer and two more over the first and third. resistance measure on pins 4-5 are 0ohm to 9.7k. That seems correct and is true on both pots.

then I go to se what happens at pins1-2-3, and they look like a solid resistor, no change when I turn it up or down. 1-2 shows 9.7k, 2-3 shows 4.5k, and 1-3 shows 4.7k. That DON'T seem correct to me, but is also true on both pots. Is that normal? or should they also vary when turning up and down?
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Old 01-11-2017, 04:57 PM   #106
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Default Re: soundcraft spirit m4 mixer troubleshooting

also, I just saw the resistor I put on this morning, is half burned out, there was this moment(I think it was just before testing and seeing most outputs gave signal) where I turned it on, saw this thin layer of smoke, switched it back of and realized i had turned it on while it was unscrewed to the chassy, and probably had a small short somewhere, thus, the resistor heated up very fast. And I know, it's naive to think nothing else happened.

But it seemed to work fine when I screwed it back in place. I WILL make a lightbulb-inseries plug before I attempt to test it live again, I promise. I will also try and find an other 10ohm resistor for that toasty r666, but that seems quite more difficult.

I'll keep on following the map back, i'm half way there anyway.
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Old 01-11-2017, 05:05 PM   #107
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Default Re: soundcraft spirit m4 mixer troubleshooting

this is why i said measure voltage across the resistor .. saying that it seemed good when you measured it so there might well be an intermittent short .
i am thinking you could add a light bulb with the resistor or in place of it for an instant visual of the short without burning up more resistors .. trouble is i am not knowing a correct value of light bulb to use ,
that was just an idea and something i have not tried myself . then again i specialise in audio amplifiers not mixers . much less complicated .
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Old 01-11-2017, 06:07 PM   #108
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Default Re: soundcraft spirit m4 mixer troubleshooting

i'm lost in the mountains, I won't be able to get anything till I get back home monday.
But I will try and get the most juice out of the tools I have here, if I can't test it live, that is tuff. I'll just try and figure out as much as I can while I'm here.

I've been testing resistors from mixl/r to the end of monitor and phones and more than half read low resistances compared to what they should, some are almost half of what they should be. all that in circuit, but I am willing to change them all if necessary when I can get hold of them.
I also found the two 75ohm(r37,r62) resistors missing that are replaced by that green wire that goes to sleeve at monitor out through the back to a gnd.

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?

Also, at what percentage of resistance loss do you think I should start replacing resistors?

And should the variable resistors(vr35/vr87) respond to the turning action at pins 1-2-3?
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Old 01-11-2017, 06:14 PM   #109
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Default Re: soundcraft spirit m4 mixer troubleshooting

resistors fail high resistance . if reading in circuit you are reading the circuit as well . so can read lower in circuit .
deal with the ground mod later if needed . i strongly suspect it was working ok like it is .
for being lazy and my number dyslexia i use things like this ..do not trust it fully though ...http://www.ohmslawcalculator.com/ohms-law-calculator
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Old 01-12-2017, 01:09 AM   #110
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Default Re: soundcraft spirit m4 mixer troubleshooting

Quote:
Originally Posted by 5inc View Post
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?

Quote:
Originally Posted by 5inc View Post
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.
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Old 01-12-2017, 01:55 PM   #111
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Default 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.

Last edited by 5inc; 01-12-2017 at 01:59 PM..
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Old 01-12-2017, 03:42 PM   #112
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Default 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
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Old 01-12-2017, 03:47 PM   #113
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Default 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..
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Old 01-12-2017, 04:08 PM   #114
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Default 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..
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Old 01-12-2017, 04:20 PM   #115
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Default 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 ?
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Old 01-12-2017, 04:22 PM   #116
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Default 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 .
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Old 01-12-2017, 04:29 PM   #117
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Default Re: soundcraft spirit m4 mixer troubleshooting

page 11 monitor & phone sections
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Old 01-12-2017, 04:37 PM   #118
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Default Re: soundcraft spirit m4 mixer troubleshooting

can you post a pic of the actual pot ?
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Old 01-12-2017, 04:38 PM   #119
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Default 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.
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Old 01-12-2017, 04:49 PM   #120
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Default 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 .
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