I've had this synth since launch and used it as a controller keyboard back in the days when I had an atari, cubase and modules.
When I left England for NZ in '99, I had to leave it behind, stored under my mum's bed. A friend bought it back last year when they visited the UK as carry on luggage, and when I got my hands on it, it unsurprisingly had issues.
It powered up, even had my custom patches still retained in memory, but I had non sounding notes on the keyboard. I obviously thought it could be an issue with the keyboard, but found some of the notes that wouldn't sound, did when the octave button was pressed, so I'm thinking the keybed is probably okay and it must be an electronics problem.

Anyone have ideas as to what might be going on? I've removed what I believe to be all the screws from the case, but can't separate the case to expose the internals. I could be being a little shy with the force used in not wanting to break it, but I'm prepared to have another go if I get some knowledgeable advice.

I'm going to sell it, if I get it fixed, to fund some more gear, so if anyone has any clues, links to guides etc, I'd be most grateful. TA.

 

Have someone look over the circuit boards for faulty (electrolytic) condensers. In some instances defect detection can be done visually, where they appear bulged, or popped. Also the wire harnesses, especially (at) the connectors, can play bad. Disclaimer: me no tech.

 

Corrosion at flat cable joints? Or even solder joints?
If all keys work at some octave switch position, that's the first thing I'd look at.
From what you tell I'd suspect that dust could be an issue too.
My next point of inspection would be everything around IC3 and especially IC7 (the SMD with 80 pins), as that's the one that manages the keybed and OCT switches.

 

I have a Juno-2 an opened it up a couple of time because I had notes not sounding and to change the battery.
I don't remember if they sounded or not when the octave was selected!!.
To open it up you have to take out all the screws around it and also the ones under that run in the middle they hold the keyboard in place. The notes not sounding on mine came from used or dirty contacts under the keys that did not trigger anymore.

Ounce you have taken out the springs, the black and white notes you will see a strip of rubber with all the little round metal contacts under it.
With time these get oxidized and they have to be cleaned or changed and then it will be as brand new.
While you have it opened might as well do that job so to have no come back if you want to sell it.
The Junos are becoming vintage synths now and getting rare and pretty expensive.
I will never sell mine as I bought it new when it came out and for a long time was also my main midi controller and I also have the PG-300 programmer.

Also my battery was dead. Might as well check out the voltage at the same time.
Changing it is not an easy job because it is soldered to the motherboard and need a tech to do a good job.
Hope this be of help to you.. good luck.

 

Thanks for the replies

I'll have another go at opening it up and trying some of your suggestions. Fingers crossed.