[sdiy] juno 60 death

[gregory zifcak]

great! thanks for all the suggestions. i'll go at it again in a day or two 
and let you all know how it turns out. now to look around for a rectifier.
greg


>From: "Gavin" <elmystico at earthlin.net>
>To: Ralph Karsten <ralph at atma-sphere.com>, gregory zifcak 
><zifcak at hotmail.com>
>CC: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] juno 60 death
>Date: Mon, 10 May 2004 12:51:27 -0400
>
>I would replace the bridge rectifier first, it's cheaper and easier and 
>they
>always go on juno 60s because they're rated right at what the synth draws 
>in
>current.
>----------
> >From: Ralph Karsten <ralph at atma-sphere.com>
> >To: "gregory zifcak" <zifcak at hotmail.com>
> >Cc: synth-diy at dropmix.xs4all.nl
> >Subject: Re: [sdiy] juno 60 death
> >Date: Mon, May 10, 2004, 12:04 PM
> >
>
> >Hi Greg,
> >
> >I have a project for you. Lots of Japanese-built transformers have 
>internal
> >fuse links that are supposed to fail if the transformer gets too warm. I
> >have seen many of them fail for no good reason. It sounds like your
> >transformer died without apparent cause, as from your description the
> >filter caps are still storing a bit of energy and you are detecting 
>normal
> >leakage in the transformer.
> >
> >So...
> >
> >If you remove the transformer and *gently* disassemble it, sometimes you
> >can fine the thermal fuse tucked into the windings. Usually it is just a
> >little metal part with two wire attached to it and nested just under the
> >tough paper exterior (which may be convered by metal end bells) of the
> >transformer. Thus the *gentle*..- you have to cut away the paper without
> >cuting any windings or wire!
> >
> >If you are lucky, the thermal fuse is blown and all you have to do is
> >replace it and patch things up.
> >
> >If not, you wasted a little time on a bad part.
> >
> >Good Luck!
> >
> >-Ralph
> >
> >On Sun, 09 May 2004 21:51:46 -0700
> >"gregory zifcak" <zifcak at hotmail.com> wrote:
> >
> >> ok,
> >> i measured correctly this time, and i'm getting 0 volts ac at the 
>outputs of
> >> the transformer. i am getting 120 volts going in, so i'm pretty sure 
>the
> >> problem is the transformer itself. nothing looks burnt though. it seems 
>like
> >> all the blown transformers i've see show some sign of damage. could 
>anything
> >> else possibly be causing this? strangely, i read a small amount of 
>voltage
> >> *between* the windings. also, the voltage regulators seem to show a 
>small
> >> voltage present (?). if it is the transformer, are replacements 
>available
> >> anywhere? is the combination of 18vac center tapped plus 8vac common at 
>all?
> >> thanks for any suggestions.
> >> greg
> >>
> >>
> >> >From: "R. D. Davis" <rdd at rddavis.org>
> >> >To: gregory zifcak <zifcak at hotmail.com>
> >> >Subject: Re: [sdiy] juno 60 death
> >> >Date: Fri, 7 May 2004 21:20:28 -0400
> >> >
> >> >Quothe gregory zifcak, from writings of Fri, May 07, 2004 at 
>09:45:21AM
> >> >-0700:
> >> > > thanks for the help everyone. i'm going to go over there again this
> >> >evening
> >> > > and take a closer look. i must have been metering wrong because 
>nothing
> >> > > looks damaged. i didn't see any fuses after the mains fuse at 
>first;
> >> >that
> >> > > will be my next task. then i'll disconnect the transformer and 
>measure
> >> >the
> >> > > ohms. anyone know if there's a schematic online? thanks again for 
>all
> >> >the
> >> > > help.
> >> >
> >> >Haven't seen one on-line anywhere... got my schematic from Roland
> >> >back in 1997.  Once you verify that the transformer is ok, and 
>producing
> >> >the correct output voltages, here are some things to check next:
> >> >
> >> >Looking at the PCB, find capacitor C2, 0.1uF (between fuse F1 and two
> >> >of the filter caps, just above C3), or the junction of C2, C1, the +
> >> >terminal of the bridge and the input of the 7805.  At that point, you
> >> >should measure approximately 9 to 10 Vdc.
> >> >
> >> >At the output of the 7805, where it forms a junction with C4 (0.1 uF)
> >> >and the + side of C3 (10uF), you should measure 5Vdc.
> >> >
> >> >On pin 4 of IC2, a TA7179P, where it forms a junction with R4 (1 ohm,
> >> >1/2W), D5 and R5 (10K, also connected to a 10K trim pot, VR1), you
> >> >should measure +15Vdc, +/-10mVdc.  If this is off by more than 10mV,
> >> >then you'll need to adjust the 10K trim pot, VR1 (see above).
> >> >
> >> >On pin 11 or IC2, at the junction with R3 (1 ohm, 1/2W), C13 (0.1 uF),
> >> >C14 (10uF) and D4, you should measure -15Vdc.
> >> >
> >> >Let us know what you find.
> >> >
> >> >--
> >> >Copyright (C) 2004 R. D. Davis The difference between humans & other
> >> >animals:
> >> >All Rights Reserved | My VAX | an unnatural belief that we're above 
>Nature
> >> >&
> >> >www.rddavis.org | runs VMS & | her other creatures, using dogma to 
>justify
> >> >such
> >> >410-744-4900 | doesn't crash!| beliefs and to justify much human 
>cruelty.
> >>
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