[sdiy] Dumbest Mistakes with Synths Contest Anyone?

[R. D. Davis]

Quothe Sean Costello, from writings of Thu, Aug 03, 2006 at 04:50:38PM -0700:
> My dumb Juno-60 mistake:

> I had a held chord on a Juno-60, using it to test a Univibe I had purchased
> that did not have the expression pedal. The Univibe was open, so that I
> could use a flashlight on the photocells. The case of the Univibe made
> contact with an uninsulated transformer connection for the power supply,
> there was a huge spark and a puff of smoke, and the end result was a busted
> Univibe (maybe just the fuse) and a Juno-60 that would always hold notes
> whether you wanted it to or not (which I sold for $75).

Wow, sorry to hear about your Univibe and Juno-60... do you still have
the Univibe?  Just wondering about the fuse... it's a shame that you
don't still have the Juno-60, since it looks like the hold problem
would have been fairly inexpensive and easy to fix... either a
transistor, switch, a resistor, or, worst case, a CPU chip itself (I
don't remember if it's socketed), since the switch turns on/off a
transistor which sends a signal to a pin 1 of the 8049C-238 CPU; to to
replace that with the specified replacement CPU chip, 8049C-380, the
reset circuit would have needed a simple modification: the addition of
a diode placed in parallel with a capacitor.  Alas, a Google search
doesn't show anything for 8049C-380, and there aren't that many
listings for 8049C and CPU, so replacing that may not be as trivial as
I thought... but just replacing it with any 8049C, and adding the mod,
might be worth a try if anyone needs to do that.

The Juno-60's seem to be more fragile than I thought.  I'm surprised
that plugging the output of a fuzz box, which had a dead battery, BTW,
so no voltage from that should have gone into my Juno-60 when I
accidentally plugged its output into the Juno-60's output.  I would
have thought that I'd have just damaged an output op-amp or some-such,
but not the tuning of certain keys going being wrong (I'm beginning to
think that the problems may be on both the the cpu board and chorus
board) can't get it into test-mode, since the key transpose switch has
always been flaky... pressing that switch rarely works, something else
I've been meaning to fix.  Anyway, hopefully I'm wrong about multiple
things having gone bad on this synth... time to open up the case and
start poking around in there, starting with a look at the
power-supply's output.

With all the hot weather we've had, I'm also starting to wonder if
Juno-60's failure happening around the time of the plugging of the
unpowered fuzz-box's output into the Juno-60's output was just a
coincidence... voltage spikes, brownouts, overheating, etc. maybe?
Has anyone else here had a Juno-60 exhibit strange failure symptoms
during or after a heat wave?  

At least I can still use this synth as a Midi controller with the
Kenton box, but that's not as much fun as a fully-functional Juno-60.
The fat bass is gone... and what fun is a Juno-60 without that?

-- 
R. D. Davis 410-744-4900  Beware & halt the National Animal ID System (NAIS)! 
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