Ensoniq MR rack motherboard


I got an Mr Rack and it’s main and aux outputs seem dead. I can use it via headphone outs which are ok.

I wanted to fix the main outs, assuming that it had a separate jack board like the Mr keyboard, but to my surprise when I opened the case I have seen that the whole of the motherboard, including the outs is just a single piece.

Do you think it is possible to find the motherboard only for a decent price ?

Best regards,

I have a similar issue: no main, aux AND headphones output. You may try theSoniq guy out in San Jose, CA. I think he replaces boards for all kinds of Ensoniq gear and claims to have worked for Ensoniq back in the day. He’s pricey, in my opinion. He also requires that you send him the bummed part you want to replace. But for an entire board, he may be your only option.

Well, I’ve already emailed him a couple of days ago, but haven’t received a response yet.

I see some sort of irregular soldering just around the output jacks, on the resistors. ( fortunately, the headphone out splits before that on the motherboard ) It may be a previous fix attempt or may be the original factory soldering was not proper and has gone bad with heat. I will also show that to an electronics repair person here.

I suspect that the jack auto sense mechanism was somewhat making it tricky to repair in my case.

I would call instead of email; I left a message and he got back to me in a day.

If you need pics of my board to compare to yours, let me know; happy to send if you need them.

As far as I know there is no set of schematics that exist for the MR Rack on the net, which is too bad since we both could make use of such a doc.

As I live in a far far away Galaxy, it would cost me more to call them than the ensoniq box itself.

Here are the pictures attached that show the red resistors I was writing about. And also a general overview of the board. It would be nice to compare with yours…

Kindly note that the headphone out is also of studio quality, without any noise or hum. So I believe the normal outs would even be superior.

Thanks for sharing your board view. Here’s a complete board in hi-res for maximum zoom-in.
Looking forward to getting the sound on my MR Rack bad settled.
Curious: is your headphone/volume assembly board crooked in-place? Mine is leaning down toward the chassis.

The manufacturing date on my MR Rack is: 05/01/97
S/N: 13656


Now I’m sure my red resistors had been operated on, because the pictures you’ve sent show no trace of soldering.

I remember the headphone board was a bit loose and had a feeling of hanging by itself. I’ll double check when I open the MR once more.

Let’s keep touch on any further progress made …

Kind regards

The red components are actually diodes.

I’m betting the culprit is probably an op amp (one of those two-channel 4556 chips nearby). With an oscilloscope, you should be able to see signal at the inputs, and most likely one of them will show nothing at the outputs.

Well, today I’ve dismantled the board and have seen that it also has some soldering underneath. I still wonder how this thing even works.

I think I need a new motherboard. In case anyone wants to sell one overseas, kindly let me know…

As Sam says. The op-amps, DACs or the capacitors (for decoupling?) around the outputs are usually to blame.

Repairable by someone with some basic knowledge. I may even part with my MR rack, but it is 240v and is fully expanded, so it probably doesn’t meet your requirements?

Edit: Actually, I think they’re 100-240v switching supplies on these?

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Well I can consider that, in case the price is reasonable. I can use my existing one as spare parts. My email is guney.hanedan@gmail.com, kindly let me know .

P.s: yeah autoswitching…

If you are interested just let me know please…

Just curious if you got your audio issue solved on your MR Rack.

Unfortunately no, upon closer examination I’ve seen other soldering attempts underneath and above the board. I have to record new stuff within months so can’t spare time to fix that. Will use the headphone outs for now.


Hello - I also have the dead main outs issue on my MR Rack. Did you get yours resolved?


No I just got rid of it.