[sdiy] juno 60 death

[Ralph Karsten]

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
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> 
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