soundcraft spirit m4 mixer troubleshooting

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

i personally wouldn't use a 1/2 watt in that position . especially for testing purposes
try with power off and checking resistance from pin 4 of the ne5532 to ground . if it shows low ohms there is a short somewhere .
would also be a good idea to check voltage on negative side of c386 . to be sure its not too high .

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Yep, plenty

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

ok, the one I found seems like it's a 1/4, the size is about 6,5mm long

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Sounds like more than enough At least for testing, it should do fine.

https://en.wikipedia.org/wiki/Surfac...minal_packages

I'd be surprised if it was any bigger than a 1206 (3216 metric).

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

I don't know about smd mount resistor values... it's pretty small, like... 3mm from side to side. I found what I think is a 1/2w 10 ohm resistor, will that do?

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

10 ohms .. try 1/4 watts if you have one .
say if you put a 2 watts in you risk burning out traces and more ..think of it as a fuse .
r667 size should give you a clue to wattage .

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Yeah, "even" the stock ones will be maaaaybe 1/4watt ones. There's not a lot of current being drawn through them (maybe about 40mA at idle), so they won't need to dissipate much power (~16mW at idle).

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

sorry, only those two mentioned earlier(it's all so big and crazy my mind is playing tricks on me), trying to write it down but i'm too tired to make it readable.

Gonna search through my scavange box and if I find one I'll stick that in. It doesn't matter what size it is as long as it is not smaller right? wattwise

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

ah .i have got a feel for the way they left clues ... r667 is limiter for positive supply so r666 should be replaced with same value ..
i hope r667 is there or i will be cross with who has been playing around with it .

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Page 15, mid-right side.

where did you find r666 in the literature ? . what sheet number ? i cant see any power supply at all at this end .. there must be a similar one for the positive supply . sometimes it makes it easier to be looking for something else .i know it does each time i lose something . might be an age thing on my part though .

I got the hunch from "The opamps are ne5532, and checking the otrher opamps of masterA, it seems like the whole line is out, they all have the same 0.7v on one of the Vcc ends."

The NE5532's of the "Master A" section are all supplied from +/-V_MASTA_L (page 10), which are "created" on page 15, through R667 and R666.

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

That's just really, really weird...

If there's so many of them, don't bother

Replace that 10 ohm R666 and see what happens then.
Is it ironic that R666 was the problem?

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

What traces are cut? Were they part of that huge "grounding mod" that was done before you opened it up?

I can't take all the credit, petehall347 came up with the idea, i only "gave a name and a face" to the potential issue. Glad to hear you found the culprit, though

Although... "missing", how? Burnt off? Or desoldered?

where did you find r666 in the literature ? . what sheet number ? i cant see any power supply at all at this end .. there must be a similar one for the positive supply . sometimes it makes it easier to be looking for something else .i know it does each time i lose something . might be an age thing on my part though .

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

it's gone, desoldered.

I'm looking for the cut traces, if you mant me to say them all.

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

What traces are cut? Were they part of that huge "grounding mod" that was done before you opened it up?

I can't take all the credit, petehall347 came up with the idea, i only "gave a name and a face" to the potential issue. Glad to hear you found the culprit, though

Although... "missing", how? Burnt off? Or desoldered?

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

oops, it was you pete, bingo

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

ok, guys, I got lost in your men-talk.

I havn't seen any corrosion anywhere on the board, appart from a few cut traces.

But you hit bingo on that "-V_MASTA_L" Khron, I have been looking for that basterd for the last hour (where is it??), and r666 is missing, devil resistor.

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Haste makes waste... And we don't always have the luxury of schematics or service manuals as perfect as we'd like them.
<bad joke / gross exaggeration> That's what separates the men from the boys... <end of joke>

But as pointed out, the power supply itself is fine, since it measures fine on most / all(?) other opamps on the board.

As i've posted just earlier today, i've dealt with another Soundcraft mixer a few years ago, that had suffered a spillage, and a couple of power traces were corroded away by that.

Good call on the series resistor suspicion, though. R666 on -V_MASTA_L would be the one in question.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

well if the negative supply for those op amps is missing the supply is a very good start is it not ? then look for a current limiting resistor to check to make sure its not burned out .
if this schematic was in one piece i could have had things worked out much sooner .
p.s i have now found reference to the dual supply for the ne5532 on sheet 10 .
the ground reference is AGND for these voltages .

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

*sigh*

I'll tell you a little hint - for at least the last 3-4 decades, (dual) opamp pinouts are pretty standard. Pin 8 = positive supply, pin 4 = negative supply, etc.

I'll tell you another hint - both the NE5532 and the TL072 (as seen on the indicated page 2) are dual opamps, with IDENTICAL PINOUTS.

As pointed out in the quote / link from the first page of this thread, the power supply itself WORKS as it should. Since it does, and the rest of the mixer / bad channel up until the suspicious opamp (as tested by the thread starter with the circuit tracer) also WORKS. So what's with this sudden fixation on the power supply?

PS: You can find details about how your precious NE5532's are powered on the bottom of page 10, if you couldn't be bothered to find'em...

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

hmm... it doesn't go straight to gnd... it passes through a few caps... and it goes down to the fader chasisses.
By my ground point you mean where I put tracer and injecter gnds?