[sdiy] Noisy Power Supply

[Scott]

The supply is an HAA-15-3-A.  The smaller one that works fine is
HCC15.1.A (1amp at 12 v, .8 at15).

BY saying the positive is flat, I do mean that there was no ripple on
the scope.  That was only on the negative rail.  As far as the scope's
reference, I'm afraid I don't really know how to use a scope!  I just
have the input going to the positive (or negative) and the ground input
going to the ground on the supply.  From the looks of it (from what Ive
seen from observing my synth through it) it looks like the little spike
on the negative side goes down about 1/2 volt.  The time knob on the
scope is on 2ms and I get maybe two spikes on the screen at a time.  I
know that converts into frequency somehow..
There is no earth ground on the supply.

Why swap supplies?  The smaller one sure is lighter and takes up less
valuable cabinet space!  It's because I've got about 26 modules in that
thing.  I've only ever had about 16-18 plugged in at a time.  I never
ran into a problem w/ not having enough power, but from what I've read,
I needed a bigger supply.

One last thing, someone asked is this only when it is under a load, and
it is actually the opposite.  When I plug it in w/ no load, or w/ only
one low powered module, the problem isn't there.  As soon as I plug in a
few more modules, I see the spike.  

I can also hear a hum from the  supply itself..  (not through the
electronics, but the thing is vibrating a little)  It does have two big
caps on it.  I suppose one could be bad.  It is just a used EBAY supply.
I'd write the guy and complain, but shipping was almost as much as the
supply itself, so it's almost cheaper to buy a new (used) one.

I guess there is no way to test a cap, with just a multimeter or scope,
is there?

Thanks for all the replies!  I could have never built my synth in the
first place w/out this group!

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Needham, Alan
Sent: Thursday, June 21, 2007 7:13 AM
To: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Noisy Power Supply

Could this be model number HC15-3-A ?
      Floating 15v at 3A, remote sensing ?
        (I can't find anything like 15v 0.8A - what is it ?)

You say the positive side is flat ??? do you mean the 'scope
sees no ripple here, what is your 'scope's reference connected to?

If the second supply is only 0.8A and is running the synth OK,
   why swap?
   is it's output floating?
   is there an earth connection anywhere on the DC supply side?

	Alan, peering out of his cave

#  -----Original Message-----
#  From: synth-diy-bounces at dropmix.xs4all.nl
#  [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Scott
#  Sent: 21 June 2007 5:57 AM
#  To: synth-diy at dropmix.xs4all.nl
#  Subject: [sdiy] Noisy Power Supply
# 
# 
#  ----|/----|/----   Sort of like that.  The positive side was flat.

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