[sdiy] Juno 60 dead CPU diagnosis

Jack Jackson jackdamery at hotmail.co.uk
Mon May 11 14:49:53 CEST 2015

A small breakthrough. I found the ebay listing of the guy who sold it to the guy who sold it to me, if you follow :)

he states:

"Had it looked at by a tech, and the problem could be a broken CPU board, component or panel failure, although he is not sure - 
he says that when he put a different CPU board into it, it worked fine. Powers up okay, and all lights come on. "

So I'd say the problem is definitely on the CPU board. Straight away suspect is that the CPU IC is not the original and has been socketed. I've ordered another one from VintagePlanet but in the meantime it looks like I should check the ports that address the keyboard matrix to see if there is any activity. Another point to look at is the on board voltage reg IC for the CPU (IC51).


> From: geekon at gmail.com
> Date: Sun, 10 May 2015 09:03:55 +1000
> Subject: Re: [sdiy] Juno 60 dead CPU diagnosis
> To: rsdio at audiobanshee.com
> CC: jackdamery at hotmail.co.uk; synth-diy at dropmix.xs4all.nl
> Hi, not sure if this would work but i replaced my junos cpu with this
> one: http://midipolis.blogspot.com.au/p/minerva-manual.html
> I cant tell how cool it makes the juno. Full midi, extra envelopes etc... :)
> If you can narrow down which chip is broken, you could contact the guy
> makes it and ask what he thinks. Hes very helpful
> Cheers
> Guy
> ____________________________________
>> On 10 May 2015, at 3:00 am, "rsdio at audiobanshee.com" <rsdio at audiobanshee.com> wrote:
>> My quick skimming of the Juno 60 Service Manual shows that there are two CPU chips. Which one are you referring to?
>> Is there one of those CPU upgrade boards installed that might be replacing one of the CPUs?
>> Grab the Service Manual online and go through the adjustments section. It has expected waveforms that you can check with a scope (or maybe even an audio interface, if you make some probes with audio wires).
>> Brian
>>> On May 9, 2015, at 8:33 AM, Jack Jackson <jackdamery at hotmail.co.uk> wrote:
>>> I bought a non working Juno 60 today. During the buy I popped the lid and found one cable unplugged and another cable in its place. I put them back in the right place but no joy.
>>> Things I checked that work:
>>> 1. Power supply - Voltages are correctly adjusted according to service manual
>>> 2. Chorus - When I turn the chorus on I can hear it hiss as expected.
>>> 3. Output - Volume knob seems to work
>>> 4. Raw waveform - All show sawtooth at test point 3.
>>> 5. Patch LED display seems to allow you to choose different patches.
>>> Things I checked that dont work:
>>> 1. VCA output
>>> 2. Gate output
>>> 3. Keyboard - keyboard seems to have no effect on raw waveform frequency at test point 3.
>>> 4. Test mode doesn't seem to do anything
>>> I suspect it could be a dead CPU. I tried removing the CPU chip and it seems to have no effect on the operation of anything that I listed above that worked - including the patch memory LED display.
>>> Is there a way I could tell for super sure it is the CPU? If it is a dead CPU, what could have killed it? If it's dead where I can get a new one for cheap?
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