[sdiy] Kurzweil power problems and bad diode?

[megaohm]

As far as checking the caps go: What should I be checking for?
And on a related note, how does one go about discharging an electrolytic
capacitor? I know there have been long discussions in the past on the proper
way to discharge a cap. I don't want to use the screw driver method. Could
anyone give a step by step instruction on how to do this properly? Sort of
an "idiot's guide" to discharging caps. This would be immensly helpful.
 peng
 note: I'll post this under a different heading to make it easily searchable
in the future.

 On 11/15/05, Barry Klein <Barry.L.Klein at wdc.com> wrote:
>
> Those diodes form a fullwave rectifier feeding 4 linear regulators and a
> couple electrolytics. Check the electrolytics if the fuse blows after
> replacing the diode.
>
> Barry
>
>
> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Simon Brouwer
> Sent: Tuesday, November 15, 2005 1:02 AM
> To: megaohm
> Cc: synth-diy
> Subject: Re: [sdiy] Kurzweil power problems and bad diode?
>
> Hi Peng,
>
> megaohm wrote:
>
> > I have a K2000 that has been non-working for a few years now. Turned
> > on power. Blew fuse. Replaced fuse. Blew again.
> > It seems others have seen this same problem. The only helpful thing I
> > could find was the following post:
> >
> > > Kurzweil uses linear power supplies. Chances are one or more diodes
> > in the
> > > bridge rectifier have shorted, causing AC to be fed to the DC
> smoothing
> > > capacitors, which have a low Equivalent Series Resistance and look
> > like a
> > > near dead short at 60 hertz. This type of failure is likely and the
> > probably
> > > cause of blown fuses.
> > > Diodes fail for two reasons: power surge and inrush surge at power on.
> A
> > > surge arrestor may cure problem #1, but the best remedy for #2 is to
> > avoid
> > > frequent power cycling, thus reducing your chances of diode failure.
> > > If it were my unit, I'd get a VOM and buzz out the diodes (after
> > > disconnecting power and also the transformer secondary coil from the
> > diode
> > > bridge) and see which are shorted. They can probably be replaced
> > with off
> > > the shelf varieties available at Radio Shack, etc.
> > > Failing that, it's off to factory service. And if it's a new unit
> under
> > > warranty, that's the way to go.
> >
> >
> > Tested the diodes and three of them measure 0.530 or there abouts.
> > One measures 0.0001 so I'm guessing this needs replacement.
> > It is a 1N5401. I'm wondering if this might be the proper fix/
> diagnosis?
>
> You can be sure that the diode is blown, so it should be replaced
> anyway. It is possible that the blown diode is not the primary cause of
> the problem (it could have been blown due to the failure of other
> components) but 1N5401 is not expensive, so it wouldn't hurt to just
> replace it and try if the unit works again.
>
>
>
> --
> Vriendelijke groet,
> Simon Brouwer.
>
> >>> nl.openoffice.org <http://nl.openoffice.org> <<<
>
>
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