Place your bets... Let's fix my mixer

the_duckchild · 2024-02-13T16:09:18.360Z

I just got an Allen and Heath Xone:23 with one of the phono channels one-legged (only the left channel shows any signal…
I only actually need the line channels, but just for fun…

What do you predict is wrong with it?

I was thinking maybe cold solder joint/crack on the RCA jacks, so will try and reflow that.

It can’t be as far as the channel fader, as this works fine for the line channel (which inputs to it at the same time.

So before that… I guess it could be a faulty op amp… or a faulty pot (although a bit of prodding with a multimeter suggests probably not.)

any bright ideas out there?

image859×1008 111 KB

p.s. Yes, I know this is a bit like asking “how blue is the sky”, but you know, collective brain power and cosmic coincidence might just work!

Geologist · 2024-02-13T16:46:16.668Z

Well, this case asks for some probing in order to pinpoint the problem.

What I can suggest:

Do the stupid: connect the cable and reverse the plugs to double check its not the cable
Double check all mixer settings so you are sure its not a routing issue with filters, fx, etc
Open the mixer and keep the cable connected and gently wiggle some parts to check if the sound comes back. Which indicates a loose connection somewhere
Get your multimeter and compare values to the working channels if those are identical. That might give you some clues
If you can easily remove the opamps, you could swap them out with a working channel to see if that fixes the issue

Good luck!

And as you say you don’t need the phone channel, be careful not to break anything else. Accidents do happen when repairing.
Also, if you would need an extra phono in the future, you could always buy a phono preamp and connect the turntable to line input.

Geologist · 2024-02-13T16:48:02.193Z

And one tip I forget: clean the phono input sockets. Dirt or rust can be a bitch for getting a proper connection

soup · 2024-02-13T17:11:31.457Z

DJ mixers often get worn the fuck out. I bought a similar mixer (different brand) a year or 2 ago and the previous owner had foolishly put caps on the phono ins which made them stick out so if the mixer was placed on it’s rear it put pressure on the phono jacks and torqued them enough that one of the channels ripped out. Similar result one phono channel only had one side. It required kludging a new connection (or replacing the jacks) as there was nothing left to reflow. Something similar wouldn’t surprise me.

cema · 2024-02-13T17:12:22.804Z

Good tips, my bets on mechanical issue or cold solder joint.
Op amp? Probably not.
Use your finger as a probe.
Because the phono amp is very sensitive it is a nice trick to make some noise by touching components to discover the audio path until you hear the missing channel. Then you can make a guess where is the break in the circuit.
Of course watch out for high voltage parts but they are well separated if not external.

HoldMyBeer · 2024-02-13T17:13:35.441Z

Sounds like a bad flux capacitor, great scott!

soup · 2024-02-13T17:20:32.039Z

Are you a thief? It seems like you have a mouth full of gold teeth.

the_duckchild · 2024-02-13T17:29:08.837Z

hmm, wondering about that potentiometer now.
No signs of any physical problems. May have to try some signal tracing as suggested!

the_duckchild · 2024-02-13T20:00:04.303Z

For anyone on the edge of their seat here I am going to make one of these and trace the signal through the good channel to hopefully track down the issue

https://diy-fever.com/misc/audio-probe/

the_duckchild · 2024-02-29T10:16:49.581Z

Ok, so the audio signal doesn’t even get as far as the gain pot for the channel.

This feels like it narrows it down to a very small part of the board.

I can’t see any physical damage.
The pot looks a bit short of solder. Maybe try reflowing that, but the complete lack of signal makes me think it might not be that.

beyond a short/bad connection it’s only really a few resistors and caps and an op-amp

JRC 8080 518RF from reading the other channel’s chips… the one on THIS channel is missing some of it’s text.

Any electronics experts out there have an opinion on whether that might be a sign that it’s been very hot/overloaded at some point?

U1A below.

Allen & Heath2287×2410 1.39 MB

side question: assuming someone might have plugged a loud-ish line level signal into the phono stage am guessing this could potentially be enough to damage the op-amp?

anyone? Bueller?

guga · 2024-02-29T17:23:58.745Z

it seems like there’s something right below/sides of R6A and i’m not sure if there’s an excessive amount of maybe soldering flux on the board or someone spilled something on it…

the_duckchild · 2024-02-29T17:26:32.622Z

oh, you’re right R6A looks well dodgy, thank you!
I knew I should post this here

yeah, might clean it too, maybe it’s a beer spill!

the_duckchild · 2024-03-04T09:50:23.641Z

update as I know everyone will be on the edge of their seats…

cleaned it. Tested the resistor at R6A (admittedly in circuit, but there are three other resistors to compare it to)

the resistor reads fine for 47k.
So do two of the others… but R43A of them reads 1.9k.

As film resistors can fail to a lower resistance, I am hoping I may have found the issue.
Time to get out a magnifying glass and some tweezers and attempt to hand solder an SMD resistor… ulp.

cema · 2024-03-04T12:33:39.817Z

R43A together with C22A forms a passive low pass to filter out some ultrahigh noise picked up by the cable. The C is also a suspect and the jack itself.