Question for the Mixwizard techs.

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LP2006

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My 16:2 DX Mixwiz has got a bit of ground loop action going on. Also, I broke a ground lead off the PCB and need to solder it back on :D. However, The amount of hum before and after I cut the lead was the same.

I'm looking for a fix. I gave the local A+H tech a call and he wanted up to $300 to fix it :eek:. I don't really feel like paying $300 for someone to switch out some capacitors. I can do that. What I need to know is: How do I take apart the case to get to where I need to go? Am i on the right track if I'm thinking its the electrolytic capacitors on the power supply that need to be replaced? Also, does anyone have/know where I could get a hold of a service manual?

Also, I wouldn't mind switching the D/I outs to prefader while I'm in there. So where do I do that?

Thanks a ton to any responders.
 
My first port of call would be the Allen & heath website.

A few years ago I bought an old A&H Saber 24/16/16/2 an absolute beast of a consol. A few emails to A&H support and they emailed me back the schematics for the whole desk and power supply. That was for a 20 yearold desk. Their tech support was amazing.

allen&heath/
 
you said ground loop hum and then you want to change the supply caps???? the two are Not related....if you pull all the cables can you still hear the hum in the headphone???? if so then do the supply filters... if not then by process of elimination trace the hum down to what peices it's coming from.... double check your cables... and make sure everything is traceable back to a single leg on the fuse box... is this a recent developement??? or a new install??? a few new peices???
 
Hum isn't always or probably even usually from a ground loop. You say you broke off a PCB lead but you don't know how to open the case :confused:

Try resoldering all the ground connections on the PCBs, and replace the ground wire between them if necessary (the PCBs have extra ground pins for that purpose). Make sure the lead that grounds the case is correctly reconnected when you reassemble the case.
 
There is a reason why Allen Heath charges so much for the repairs. First, they are authorized, and have both the schematics and the expertise, as well as all the proper equipment to diagnose and repair and even restore the console to stock operation. Second, the mix wiz is a cheaper console. One of the ways they make things cheaper is by using different schemes when building the console. The channels in a Mix wiz should have a lot of buss ties that run across all of the channel sets rather than being modular or even semi modular like nicer desks would be. When you do finally get the mixer open you will notice that all of the PCB's for the channels are very close together and very tight. This makes it hard to work on and very time consuming to completely dissassemble it to get in to work on different areas of the console. One of the major drawbacks to a cheaper design like this is that when you have a problem in one channel the same issue can track across multiple channels whereas in a modular system, the different features are more isolated and usually much easier to track down. Also, be very careful because the Mix Wiz consoles are known to have problems in the ribbon cable that allows the i/o section on the back to swivel. The ribbon cables get very stiff and crack and/or break too easily.
 
mshilarious said:
You say you broke off a PCB lead but you don't know how to open the case :confused:
Click to expand...

Sorry, I should have specified:

I figured out how to get to the rear panel/power supply PCB. At least the back of it. I don't think I figured out how to get to the component side of the PCB. (Just the solder joint side)
 
dementedchord said:
you said ground loop hum and then you want to change the supply caps???? the two are Not related....if you pull all the cables can you still hear the hum in the headphone???? if so then do the supply filters... if not then by process of elimination trace the hum down to what peices it's coming from.... double check your cables... and make sure everything is traceable back to a single leg on the fuse box... is this a recent developement??? or a new install??? a few new peices???
Click to expand...

The hum is without any cables plugged into the board. It is coming out of every output of the board: Direct outs, mains, auxes... you name it. Even the insert points.

I need some specification on the supply caps vs. the filter caps. To my understanding, electrolytic capacitors are used in power supply circuits as filters. Maybe I'm way off there...

If I'm not looking for electrolytic caps, what kind of component am I looking for that serves as a filter?
 
electrolytics are used for filtering the power supply yes... sometimes the terms are used interchangablly... there are also small electrolytics some times used in EQ and coupling caps as well... the fact that the humm is there with nothing plug in does point to the supply caps as the place to start.... do have a buddy that owns an osciloscope???
 
yo tried contacting A&H yet or did the easiest solution go over your head?
 
using the scope take a DC measurement of the supply rails... then a reading of the amount of ripple on the rail as a % of the total.... ie if the rail voltage is 20v and the ripple is 2 v the you've got 10%ripple... make sense????below 5% is generally not bad but down around 1% is way better... if there's more one one side... thats your bad filter cap... although ya might want to just replace both and be done with it...
 
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