substitute

Soundcraft Spirit Mixer stuck in PFL solo mode
« on: June 01, 2018, 09:04:36 PM »
Hello, hello, hello, looooooooooooooong time no see.

I have a Soundcraft spirit folio mixer that is stuck in PFL SOLO mode that I'm working on.  Here are the details

- The SOLO indicator LEDS on the two stereo channels are constantly on regardless of switch position
- The master PFL indicator LED is constantly on and the master meters behave as though it is in PFL mode
- Even though the SOLO indicator is on either way, audio from the stereo input channels doesn't route to the PFL buss unless the switch is depressed
- The SOLO switches on the channels test appropriately for continuity and behave as expected

I'll attach screen shots of the SOLO area of the schematics for both the stereo channels and the master section following this post.

Here is a link to the complete service manual, pages 18 and 21 are what I'm looking at.
https://www.dropbox.com/s/siya6u7guwva0zd/soundcraft_spirit_folio_racpac_sm.pdf?dl=0

Here's a link to the user manual
https://www.soundcraft.com/en/products/spirit-racpac

My current suspicion is that some component (perhaps Q3) in the master section has failed and is letting the +17 supply through to the EN buss and also activating the main PFL LED.
« Last Edit: June 02, 2018, 06:20:20 AM by substitute »


substitute

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #1 on: June 01, 2018, 09:05:18 PM »
Stereo Input Solo detail attached

substitute

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #2 on: June 01, 2018, 09:06:00 PM »
Master PFL detail attached

JohnRoberts

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #3 on: June 01, 2018, 11:31:21 PM »
it's after beer o'clock so I will just answer in general.

Look for something wrong with the solo/pfl logic bus...  it may be shorted or floating at some incorrect voltage.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

substitute

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #4 on: June 02, 2018, 06:23:14 AM »
It is (or was) and on a Friday no less. Now it's coffee o'clock. Unfortunately the schematics don't have any voltages notated and I don't know enough about these types of transistor switching circuits to know what to expect. I'll post back with voltage measurements a little later.

substitute

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #5 on: June 02, 2018, 08:24:08 AM »
Here's some intel for the transistors in the master PFL section...

Q3
B 16.35v
E 17.02v
C 17.91v

Q4
B 6.79v
E 0v
C 16.33v

Q5
B -16.26v
C -16.85v
E -16.84v

Q6
B -0.64v
E 0v
C -0.14v

Does anything jump out at anyone?
 

JohnRoberts

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #6 on: June 02, 2018, 11:25:06 AM »
Here's some intel for the transistors in the master PFL section...

OK there is trouble in PFL 'ville
Quote

Q3
B 16.35v
E 17.02v
C 17.91v
Q3 is almost valid... it appears turned hard on, while a little unusual for collector voltage to be higher than emitter that is pulling it up.  I will ignore that as a measurement artifact.
Quote
Q4
B 6.79v
E 0v
C 16.33v
now your talking,,, Q4 is busted. Unless base is actually 0.67V instead of 6.7V  :o
Quote
Q5
B -16.26v
C -16.85v
E -16.84v
q5 looks OK
Quote
Q6
B -0.64v
E 0v
C -0.14v
q6 looks OK..
Quote
Does anything jump out at anyone?
Recheck base voltage at Q4, if actually 6.7V that is your problem.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

substitute

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #7 on: June 03, 2018, 09:38:48 AM »
Just double checked, the base of Q4 is indeed 6.7v.  I'll report back once I've replaced it.

Thanks for the insights!

moamps

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #8 on: June 05, 2018, 04:05:47 AM »
Q3
B 16.35v
E 17.02v
C 17.91v

Collector of Q3 can't be on higher potential than emitter. Check this transistor also.
Q3 should have base or emitter resistor, or it is just schematic error.

substitute

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #9 on: June 05, 2018, 07:21:53 AM »
Will do.


JohnRoberts

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #10 on: June 05, 2018, 12:26:29 PM »
Collector of Q3 can't be on higher potential than emitter. Check this transistor also.
Q3 should have base or emitter resistor, or it is just schematic error.
I already ignored that as a measurement artifact (error) since the PS rail voltage is 17V making 17.9V extremely unlikely.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

JohnRoberts

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #11 on: June 05, 2018, 12:27:13 PM »
I already ignored that as a measurement artifact (error) since the PS rail voltage is 17V making 17.9V extremely unlikely, and a bad transistor will not generate extra voltage.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

moamps

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #12 on: June 05, 2018, 05:11:33 PM »
I already ignored that as a measurement artifact (error) since the PS rail voltage is 17V making 17.9V extremely unlikely.
What's more confusing to me is connection of Q4 and Q3. It can't work that way.

JohnRoberts

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #13 on: June 05, 2018, 06:13:03 PM »
What's more confusing to me is connection of Q4 and Q3. It can't work that way.
I suspect there are parts missing off the page,,, like a resistor in series with base of the npn to keep collector current modest.

it is not unheard of for mistakes in old hand drawn schematics.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

abbey road d enfer

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #14 on: June 05, 2018, 06:30:44 PM »
What's more confusing to me is connection of Q4 and Q3. It can't work that way.
Why? Seems perfectly legit to me. Collector of NPN Q3 sinks current from base of PNP Q4.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

moamps

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #15 on: June 06, 2018, 03:49:19 AM »
Why? Seems perfectly legit to me. Collector of NPN Q3 sinks current from base of PNP Q4.
Q4 is NPN, Q3 is PNP. Both work as switches. What's the base current of Q3 when Q4 is in ON state?

abbey road d enfer

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #16 on: June 06, 2018, 04:33:59 AM »
Q4 is NPN, Q3 is PNP.
That's correct, so Q4's collector sinks current from Q3's base.

Quote
Both work as switches. What's the base current of Q3 when Q4 is in ON state?
Obviously there's a mistake regarding Q3's collector connection. It should go to R183.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

moamps

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #17 on: June 06, 2018, 04:44:17 AM »
Obviously there's a mistake regarding Q3's collector connection.
I don't think so.  A resistor in base or emitter of Q3 is missing, as I already stated.
« Last Edit: June 06, 2018, 04:53:15 AM by moamps »

abbey road d enfer

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #18 on: June 06, 2018, 05:04:55 AM »
I don't think so.  A resistor in base or emitter of Q3 is missing, as I already stated.
You're correct, I didn't see that Q5 is taking care of the LED.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

JohnRoberts

Re: Soundcraft Spirit Mixer stuck in PFL solo mode
« Reply #19 on: June 06, 2018, 01:21:29 PM »
I am repeating myself but it is pretty common to find transcription errors in hand drawn schematics (like all were decades ago).  Also there may be circuitry not shown off that schematic page limiting base current.

As usual don't ASSume that every schematic is accurate (or reported measurements for that matter).

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.


 

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