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Old 01-12-2017, 05:16 PM   #121
5inc
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Default Re: soundcraft spirit m4 mixer troubleshooting

good one, I'll add that to my workflow.
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Old 01-13-2017, 05:21 PM   #122
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Default 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.
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Old 01-13-2017, 05:27 PM   #123
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Default Re: soundcraft spirit m4 mixer troubleshooting

resistors fail high so i guess you measured in circuit ? unsolder one leg for proper testing .
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Old 01-14-2017, 05:16 PM   #124
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Default 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.

Last edited by 5inc; 01-14-2017 at 05:55 PM.. Reason: been corrected
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Old 01-14-2017, 05:26 PM   #125
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Default 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.
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Old 01-14-2017, 05:33 PM   #126
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Default 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.
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Old 01-14-2017, 05:54 PM   #127
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Default Re: soundcraft spirit m4 mixer troubleshooting

oops my bad that was VDC
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