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The mixer lights up the clip lights when the switch is off and plugged in cold! Interestingly, the switch just clicked it's last click, does not latch on anymore. While investigating the switch I noted that inductor L10 (10uh) is cracked. I guess I need to investigate the power supply section a bit more as well. 
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With the switch completely removed, the console powers up normally (except blown channel 3). How is this possible? This mixer has an outboard 15V smps, and the boards are out of the chassis, so it's not finding a chassis ground. Is it finding a ground through D7 or D6? I suppose I don't quite understand what the purpose of the circuity before the voltage regulator is.
If I jumper switch poles 1->2 and 4->5 all the mute/clip lights come on.Comment
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Look at your schematic snippet, the power switch does not interrupt the power into the mixer. it only controls Q39 and whatever that detect line goes to. Putting up the entire page that power supply came from would be useful.
L10 looks OK to me, the crack appears to be in the plastic holder.Education is what you're left with after you have forgotten what you have learned.Comment
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Hey Enzo,
Yes, the switch appears to connect the -15v part of the circuit to ground I think.
Here's the full Master section schematic. Power section is on Page 3 upper right hand corner.Comment
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I guess it is working without the on/off switch present because the Voltage regulator U67 is getting ground reference through the D7 diode next to the switch? How is it supposed to turn off then? I'm not super clear on what the Q39 part of the circuit does for a living. Should I investigate that area and also Q4 and surrounding parts? Is that what is responsible for turn off duties?Comment
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There's also "TIE THIS GND DIRECTLY TO PWR INPUT JACK J26" I don't know what J26 the are talking about....Comment
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Aside from you can't turn it off, are ALL the mixer troubles fixed?
U67 doesn't really have a ground reference. The "ground" pin on the chip sits on the -15v line.
Your incoming power is +15v and chassis ground CGND. Now look over to the right, soo those zero ohm resistors? They connect all the grounds together. GND0, GND32, GNDLED, GND10, and DGND. All bond the grounds togetherEducation is what you're left with after you have forgotten what you have learned.Comment
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Maybe I upset something because It is/was missing chassis ground? Boards are on the bench out of chassis...Comment
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I'm not that familiar with the Peavey, but I know some of the Mackie boards don't like to run out of the chassis. Grounds are carried through the chassis via the jacks being tightened into the steel chassis. I'll often use clip leads to complete ground circuits when boards are out of the chassis. Perhaps that's some of the problem."I took a photo of my ohm meter... It didn't help." Enzo 8/20/22Comment
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As far as I can see the power supply takes in +15 and makes -15 from it, providing +15 and -15 to the mixer. I don't see other power, and if this mixer has phantom, is it only running at 15v? In any case, as I see it from here, the power supply stands on its own.
U67 is the switcher. It has two enables, EN1 is active low and is tied to "ground". EN2 is active high. If the switch is closed, it pulls down the base of Q39, turning it on, and that pulls up the base of Q35 turning it on, which pulls EN2 down to "ground". Looks to me like that ought to turn off the IC. a closed switch also pulls down on the base of Q4, and that tends to turn Q58 off. That ought to remove both 15v supplies from the output.
Open the switch, Q39 turns off, so Q35 turns off, wwhich allows R146 to pull up EN2, turning on the IC.
SO if removing the switch leaves the thing running, I'd wager something in the Q39 and Q35 circuit is bad.Education is what you're left with after you have forgotten what you have learned.Comment
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I still have the original problem of the clip/mute light on channel 3 and 14v in all the wrong places on the opamp (again). I've flexed the board quite a bit and not found the solution through that line of testing. I have 10 more opamps arriving later this week.
Do you suspect a bad 0ohm resistor causing the won't turn off drama?? To be honest, my gut feeling when it failed was to bypass the on off switch. I'm having trouble sourcing an exact replacement in US and someone can just unplug the power just as easily as hitting the button. However, I'd like to know why it's behaving like it is.
Originally posted by Enzo View PostComment
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Thanks, I'll look into this more tomorrow. I will say that the problem did seem to happen when I had everything in the chassis as well If I'm remembering right. This mixer is comprised of 3 boards (one for the 8 microphone inputs), one for the line inputs and master, and a daughterboard for the DSP section. The chassis grounds I'm thinking of are both on the same board, so it would be easy to jump them together.
I will say I'm nervous about letting it operate too long in the all clip lights on fault mode - as I don't want to damage any more components.
Originally posted by The Dude View PostComment
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Enzo,
The guy I'm working on this for had another one of these mixers for me to look at (with a different issue which I've now fixed
). These things are disappointingly made. I was able to take some measurements on the mixers and have annotated them on the following PDF.
Readings in Blue are from the working mixer. Readings in Red are from the malfunctioning mixer. Green readings match between the mixers.
pv14psuvoltage.pdfComment
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Zero ohm resistor just means a wire. They make actual zero ohm resistors, but they are simply wire with a resistor body wrapped around it. That is easier for the assembly machine to handle than plain wire. All they are doing is connecting all the grounds together, like the right edge of the schematic says.
Where was your ground probe connected when you took these readings? Does this supply make +15 and -15 at its outputs? O dom't see how you can have 0.2v at the top of R146 when it is directly connected to the +15 rail across the top.Education is what you're left with after you have forgotten what you have learned.Comment
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Hey Enzo
All those zero ohm resistors check out.
DMM was grounded to a chassis ground. All the Chassis grounds were tied together with alligator clips for good measure.
I just reviewed my hand drawn notes that I made the PDF from. That .2 volts at the top of R146 is a mistake. I'm getting 14 volts there on both mixers. (Both rails work)
Also meant to mention - there is a separate 48v supply (boost circuit). It's just on the next page of the schematic.Comment
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