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[Asaf Smilan]

Hi,
A friend of mine gave me a 44*8*2 allen & heath ML4000 console for my home studio.
This board have some issues:
https://www.youtube.com/watch?v=mpJnTCamEA8&feature=youtu.be
* In all the input channels the faders doesn't work, the signal passing thru the board and reach to the LR out / group out / aux send, but the channels faders doesn't work.
* Mute buttons and PFL buttons doesn't work
*VCA groups doesn't works.

The three voltage LED indicators showing that the board getting the right voltage from the PSU.

Please advice how can I solve those issues?

[Ray Aberle]

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Thanks!

Ray

[Brandon Keith Blakeney]

Most likely you have a problem with the CPU board within the console, it controls all of the faders and muting system. UNFORTUNATELY, Allen & Heath has decided to no longer support these consoles and has no replacement CPU board. To repair mine I actually had to buy another console on ebay and steal the parts I needed. Fortunately, the ML3000, 4000, and 5000 all use the same CPU board IIRC.

PS, if you have the tools and skill I would take the back cover off of the console and take a look at the battery on this circuit, you might be able to replace just the battery if you're lucky. Mine had corroded to the point that it damaged the entire circuit board. 

[Asaf Smilan]

Thanks you Brandon,
I took a look on the CPU card and it seems like the battery has leaked and there's some corrosion on the chip below the battery.
The current battery voltage is 2.6V

[Daniel Levi]

Cut out/remove the battery immediately, remove the board and clean off the green stuff, a mild acidic product such as citric acid is best for this as it helps to neutralise the alkaline battery chemicals.
Next look to see if there are any damaged traces and if there are then you will need to work out where they are going and put in replacement wire links (enameled copper wire is good in these situations) and see if it now works.
The corrosion might be causing shorts that are removed once the board is clened but don't bet on it.

As for replacing the battery and easy option would be to solder in an AA/AAA battery holder and use standard batteries placed in a part of the case where if they do leak they cannot affect the board, it also makes it easier to replace the batteries when they do go.

[Bob Taylor]

Not sure what will happen if 2 AA batteries are used. That could be 3.2 Volts???

We lost our 4K the same way at my church. Battery had the same Voltage, just no corrosion like this. Our CPU was dead and did learn that there is no support for this product. Downloaded the Service Manual, i think from AH, and only the 4 and 5K use the same CPU card as I recall. there are jumpers to select model and size on the board.

Only good thing is at this time there are lots of these boards Cheap at various sale sites. At the time ours died, we couldn't find a donor.

We got to move to digital with an X32. Just love the 32 so much. (Sarcasm) Miss not having layers and everything available all the time, but i'm just an old guy.

[Daniel Levi]

Not sure what will happen if 2 AA batteries are used. That could be 3.2 Volts???

Ni-Mh batteries (which the battery in this is) are nominal 1.2v so 2 cells in series are 2.4v. The battery currently in this will also be 2 cells in series hence the 2.4V rating.

[Asaf Smilan]

Thanks guys,
The battery on my ml4000 still works fine.
I took it out from the card , added some extention wires and glued it with epoxy to the chassis.
I cleaned the corrosion and fixed this PCB (and the entire console) with a toilet cleaner (ferric chloride) and tap water!!!
Now everything works like it should.
Thanks again for your advices.

[Steve Payne]

Thanks guys,
The battery on my ml4000 still works fine.
I took it out from the card , added some extention wires and glued it with epoxy to the chassis.
I cleaned the corrosion and fixed this PCB (and the entire console) with a toilet cleaner (ferric chloride) and tap water!!!
Now everything works like it should.
Thanks again for your advices.

I love a story with a happy ending!  :-)  Congratulations.

[Asaf Smilan]

Hi,
After fixing the CPU card I'm about to finish the process of modding a 48 channel mixer into a 32 channel mixer.
The only issue that left is with the meter bridge.
All the group / AUX vu meters are working but the L, R and C meters (VU and LED) doesn't works.
I checked the vu meters with a multimeter and the meters coils aren't burnt.
I replaced the ribbon cables going from the DIST PCB to the meter bridge but there's no difference.
Any ideas how to fix this problem?

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