[sdiy] Noisy Power Supply

[Scott]

Thanks a lot, everyone.  
the filtering cap's were my first suspicion, but I wanted to get a 2nd
opinion first.  Actually there are these l-lim trim pots for both the
positive and negative, and I have no idea what they are for (the old
supply doesn't have them, and changing them does nothing to the
voltage.. I haven't messed w/ them w/ the scope yet) and something to do
with them was my 2nd guess.  I just wanted to see if anyone else
mentioned them before I started replacing the caps (cause,
unfortunately, I don't have any caps that large laying around)

I'll post back and let you know if I have any positive results

Thanks!!!!!
Scott

-----Original Message-----
From: John Luciani [mailto:jluciani at gmail.com] 
Sent: Thursday, June 21, 2007 12:18 PM
To: Scott
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Noisy Power Supply

On 6/21/07, Scott <Scott at scottwick.com> wrote:

> 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.

Since the ripple goes away without a load and the ripple is ~50Hz it
sounds like you have a linear supply with a bad filter capacitor.

After *all* the capacitors are discharged you could do a visual
inspection for bulging filter capacitors. Look at the pressure relief
device on the top of each cap. You could also take a look at the
capacitor solder joints.

(* jcl *)

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