14 Jul
2012
14 Jul
'12
11:35 a.m.
Tothwolf wrote:
On Fri, 13 Jul 2012, Chuck Guzis wrote:
If you are replacing capacitors in switching power supplies you must use
replacement caps that are high frequency and (usually, but no always)
low ESR. Same goes with recapping monitors - the caps on the B+ lines
all care a lot about high frequency response (heat factor) and the caps
in the horizontal circuit are also usually fussy.
We use (after some research which variety is needed for the specific
application) the Panasonic caps from Digi-Key or Mouser rather than
buying them from the corner supplier as generic caps just don't cut it
in a great many applications.
John :-#)#
--
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
www.flippers.com
"Old pinballers never die, they just flip out"
I'm getting around to doing some work on my
veneered and generated
HP5307A frequency counter. Looking at all the gold-plated PCB
goodness inside, the first thing that jumps out at me is a bulging
electrolytic. It's a 940 uF, 40V unit. Not 1000 uF, but 940. Not
50V, but 40V. I'm going to substitute a pair of 470uF, 50V units
paralleled as a substitute, but this had me wondering if anyone knows
why the strange values, particularly since +/-20 percent tolerances
are common on electrolytic caps.
The 940uF 40V capacitor just dates to before we had the modern
preferred values system. If it is just a filter capacitor, a 1000uF
50V should work just fine, and would likely be more reliable (and have
less leakage) than two smaller capacitors in parallel.
I replace odd value capacitors all the time in older SMPSUs and as
long as the values are close, substitutions are generally not a
problem. The hard part I've found is finding modern parts with the
same lead spacing. Sometimes you have to go up a case size and/or
voltage rating to find an electrolytic that will fit the existing
location without putting excessive bends in their leads. This is
especially true with old 3-lead "computer grade" capacitors (typically
two ground leads).