[sdiy] Kurzweil power problems and bad diode?

[Roy J. Tellason]

On Tuesday 15 November 2005 04:01 am, Simon Brouwer wrote:
> 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.

I'd replace all four of them,  and use 1N5408s,  which are the same current 
rating but *way* higher in voltage,  which will be somewhat more robust.  The 
price difference is trivial if you're not talking a manufacturing context.

-- 
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ablest -- form of life in this section of space,  a critter that can
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