Live Sound & Production

[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-fuck 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).

[OneEng]

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agedhorse wrote:

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-fuck of a show.

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Thanks Andy.

The board looks like it could take a battle field blast, but man I sure wish they had opted for removable jumpers instead of soldered in wires labeled as "jumpers".  I guess it isn't any different than using SMP 0 ohm resistors for the task .... but jumpers would have made this part of the job easy

For the channel 5 that isn't working right, I was absolutely going to remove it.  I was thinking that without any signal generator or scope here at home (I could get any number from work if I really got motivated), I could just blanket replace the input stage parts most likely to be causing this issue:

1. IC2 (TL072 op amp)
2. TR3 and TR5 (2N4403 transistors)
3. D1 and D2 (1N4148 diodes)

I could also check the gain pot to make sure it isn't messing up, but I have a feeling it is fine.

Unfortunately it is starting to look like the only option for even moving the jumpers on channel's 2-16 is to remove the channel boards  I can't get my solder sucker down in between the boards good enough to get the solder off of the leads.  I could get some solder wick (which I don't have at home either) and give that a try without removing the boards.

All of this just so I can record without clipping and not have to re-setup the mixer for live vs recording every time!

I can't for the life of me figure out why Allen & Heath ever thought it was a good idea to make the direct outs POST fader by default on these units.  I understand it is PRE fader on the MW3 (go figure).

Thanks again for all the help.

[OneEng]

Uggg,

Got the jumpers (for moving POST fader direct out to PRE fader direct out) moved without cutting the ground lines and removing all channels of the mixer from the board.

I will wait to hear from Andy to see what I want to do with channel 5.  I'll give the mixer a quick check to make sure I didn't break anything while moving the jumpers then move on to purchasing parts from DigiKey for channel 5.

[agedhorse · Accepted solution]

I found it on my service laptop, PM me your e-mail address and I'll send you the service manual.

Did you cycle the insert jack? That's the most likely cause. Check the simple stuff first.

[OneEng]

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agedhorse wrote:

I found it on my service laptop, PM me your e-mail address and I'll send you the service manual.

Did you cycle the insert jack? That's the most likely cause. Check the simple stuff first.

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Ok, Andy.  This is a PRIME example of the difference between an engineer that has the theory, and someone that actually does it for a living.

All I had to do was poke a plug into the insert slot a couple of times and it works fine!

That was great advice.  I now have all 16 channels working perfectly and the channels that I use for my band are now set to PRE fader on the direct outs!

If you have the service manual, I wouldn't mind having it around for the future.  I PM'd my email to you.

Thanks again so much for the help!

[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.