Music and Synth DIY

synth repair

Juno 60 – Noisy chorus and sticky switch repair

My lovely old Juno 60 – which you can prise from my cold, dead, hands – had developed two minor problems.

Firstly, the famously nice chorus was starting to sound like a white noise generator, putting a layer of hiss all over the signal. Noticeable noise is quite normal, but it shouldn’t sound like you’re stood in a wind tunnel.

There are several potential causes but there are lots of anecdotal reports of this happening to the MN3009 bucket brigade chips as they age (lcet’s not forget the Juno was released in 1982, making it over 40 years old now).

Depending on how much of a purist you are, you can either replace them with NOS Panasonics if you can find them and justify the price, or you can use Xvive’s MN3009 clones. I went with the latter, as I’ve used their BBDs before making and modding analog delay lines and there was no noticeable difference that I could perceive.

Got mine from Cabintech.

Firstly, we need to get the lid off. The black faceplate is hinged, which makes working on it really easy. There are four screws holding the faceplace to the “wooden” sides, two on each side. Once those are out, you can lift the faceplate back.

The chorus board is underneath the bender board. There are five screws holding the metal faceplate with the bender and volume control etc, on the underside of the synth. The bender assembly can then be removed.

The chorus board is held on with four screws, one in each corner. Remove those, and desolder the two MN3009s.

I fitted DIP sockets, because they fit, and why wouldn’t you. If your replacements weren’t working properly, you can always swap the OG chips back and if they work (apart from the noise, of course), then you can be pretty sure the fault’s with the new chips.

Secondly, the sticking Arpeggiator switch. This is really straightforward. Remove all of the slider caps for the sliders on the left hand PCB. Remove the eight screws holding the PCB to the faceplate. Slide it out.

The Key transpose, Hold, and Arpeggiator button caps lift off the switches, and all that was necessary was some switch cleaner.

Whilst you’re in there, changing the battery is almost certainly needed, given the age of the thing – I did that a while back, whilst I was fitting the excellent Tubbutec Juno 66 upgrade – which I must get round to building a dedicated MIDI controller for…

The service manual is here if you want it.