soundcraft spirit m4 mixer troubleshooting

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

No, the trace seems to end after r457 and r466, they are just after the pan pot on monochannel1, and should go to switch12 at masterA.

It doesn't dissapear, but it is greatly reduced, from there I have to turn the gain right up untill it clips to hear a faint something.

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.... gonna check master B

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

http://vakits.com/sites/default/file...uct/NE5532.JPG

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

always check data sheets and the manual ..
i know some op amps will work from single or dual voltages ..
you need to trace where pin 4 goes . and use that ground point as your ground point . that is of course its being fed with a single positive supply only .

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

i have just been all over the manual and they seem to have conveniently missed off the power supply .

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

Pin 4 will most definitely NOT go to a ground - all the opamps in this mixer are supplied with symmetrical voltages (roughly +/-13v as measured).

petehall347, have you even looked at the schematics? They're linked in one of the posts on the first page. It's best not to assume too many things, when "blindly" (no offense) instructing less experienced people to connect and test things, imho...

I don't know what ancient datasheet you dug out that picture from, but it's... inaccurate - https://cdn.badcaps-static.com/pdfs/...cb7311d307.pdf

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

Pin 4 will most definitely NOT go to a ground - all the opamps in this mixer are supplied with symmetrical voltages (roughly +/-13v as measured).

petehall347, have you even looked at the schematics? They're linked in one of the posts on the first page. It's best not to assume too many things, when "blindly" (no offense) instructing less experienced people to connect and test things, imho...

I don't know what ancient datasheet you dug out that picture from, but it's... inaccurate - https://cdn.badcaps-static.com/pdfs/...cb7311d307.pdf

i got the manual from an earlier post . what page is the power supply on ?
and yes ne5532 can be wired both ways as far as i am aware .
i did say trace where pin 4 goes to too be sure .

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

like this ...

[Khron]

Re: soundcraft spirit m4 mixer troubleshooting

You might've found the manual, but you've obviously NOT read through the whole thread (or not carefully enough).

As you can quite clearly see in the schematics, all the op-amps are NOT powered from a single supply, but from a split-supply.

Look on page 2 of the service manual, on the bottom, mid-right side. What do you see?

Yes, opamps CAN be used with a single supply, but if that's (clearly) not the case here... What's the point?

whoa, I think I should have re-read my post after replying, it is a bit unllegible, sorry about that.
I was reading volts, and i had the black lead on the chassis holding the boards.

And yes, CN6 has a 42V at pin 1, +13,7v at pins 3-4, and the negative at pins 9-10.
And CN9 has correct voltages at 3-4, 9-10.

https://www.badcaps.net/forum/showpo...30&postcount=5

"The negative", in this case, is the -13.7v at pins 9-10 of CN6.

[petehall347]

Re: soundcraft spirit m4 mixer troubleshooting

You might've found the manual, but you've obviously NOT read through the whole thread (or not carefully enough).

As you can quite clearly see in the schematics, all the op-amps are NOT powered from a single supply, but from a split-supply.

Look on page 2 of the service manual, on the bottom, mid-right side. What do you see?

Yes, opamps CAN be used with a single supply, but if that's (clearly) not the case here... What's the point?


https://www.badcaps.net/forum/showpo...30&postcount=5

"The negative", in this case, is the -13.7v at pins 9-10 of CN6.

ok i am on sheet 2 and cannot see a single ne5532 or any reference to the power supply for them . this manual is one of the worst i have ever seen .. its more like a bloody car wiring diagram with numbered wires .
and where is the actual regulated supply diagram ? this is where to start as i suggested at the start of this thread .

[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?

[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...

[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

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.

[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.

[5inc]

Re: soundcraft spirit m4 mixer troubleshooting

oops, it was you pete, bingo

[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

it's gone, desoldered.

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

[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 .

[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?

[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.