Mix Wiz Overhaul (a little help?)

[OneEng]

Hi guys,

I have a MIxWiz 16:2 DX (not mixwiz3)

From my understanding, there was an original MixWiz, a MixWiz DX and a MixWiz3.  For reference, my mixer does not have the lamp light in the upper right hand nor does it have a mono fader (only 2 yellow left and right output faders).

I recently got the schematic for this mixer hoping to diagnose an issue with channel #5.  In looking over the schematic, I also figured out why my recordings with my new Zoom R16 were getting channel clipping.

As it turns out, this version of the MixWiz has the direct out's on each channel POST fader which means that if the combination of the gain and fader get above ~2-4db, I get clipping on my recording.

I decided to open it up and do a little investigating to see what it was going to take to move the "jumpers" to make the direct outs PRE fader .... and while I was in there, try to figure out why channel 5 is mis-behaving.

Getting the back off of the mixer wasn't bad, but that is where the good report card for maintenence ends!

This board is obveously an older design.  The channel strips are comprised of all through-hole components mounted on a single sided board.  That wouldn't really bother me so much, but it appears that power and ground for each channel strip board is provided by a pair of bare wires that traverse ALL 16 channel strips and then the wire is soldered in place on each board.

What this does is makes it so that you can't just unplug a couple of ribbon cables, remove the knobs, and pull the board out. 

Has anyone delt with these before?  Do you just snip the power and ground runs and pull the board out and then when you put it back together, splice the power and ground lines back together?

Secondly, channel 5 is acting badly.  It distorts horribly with only minor input.  If you put the pad on, you can get a clean signal, but not enough output.  Any thoughts?

I have to imagine that the MixWiz3 was better designed for manufacturing and repair than this .... or at least I hope so for Allen&Heath's sake!

Any advice would be appreciated!

[Unalaska]

The mixwiz like most boards aren't meant to be user serviced, that said I did replace some broken pits on mine on ch 2-4.

 

I ended up unsoldering the copper wires from ch1 thru 4 and peeled them back, but not cutting anything. The cards will come out and you can work on them separately. For what you're describing. Wouldn't bother trying to fix it myself, id buy the whole card

[agedhorse]

Through hole is grest, easy to service.

Probably best to snip the grounds (IIRC there is a switching ground and a quiet ground) and remoce the PCB

Most likely problem is a damaged gain pot or something in the input diff amp feedback network. I think I have the S/M for it, will look tomorrow when I get baqck to the shop after thes cluster-{censored} of a show.

[OneEng]

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Unalaska wrote:

The mixwiz like most boards aren't meant to be user serviced, that said I did replace some broken pits on mine on ch 2-4.

 

I ended up unsoldering the copper wires from ch1 thru 4 and peeled them back, but not cutting anything. The cards will come out and you can work on them separately. For what you're describing. Wouldn't bother trying to fix it myself, id buy the whole card

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That was my first thought as well, but I was told they no longer carry the part

That was when I decided to put my much rusty tech skills to the test (despite popular perception, I can assure you that most engineers solder horribly).

[agedhorse]

Indeed, this is where 30 years of engineering experience in this particular field is helpful, but I have also been responsible for reliability and failure analysis in pro audio and M.I. products which is just as valuable when designing new products. Not as sexy, but the important stuff rarely is.