[Boatanchors] 'Stoopid' OT question

[Glenn Little WB4UIV]

Use 105 degree C capacitors rated for the highest current that you can 
get to fit into the available space.
If you cannot measure the ESR, play it safe and replace all of the 
electrolytic capacitors, that is, unless you just like going to the site 
to replace another failed capacitor.

73
Glenn
WB4UIV

On 8/11/2017 10:30 PM, Phil wrote:
> Hi,
> 
> Right now I have a Samlex SC1223 12V switching PS on the bench.  It was 
> used on one of the remotes for the club W6BXN repeater system.  Anywhoo, 
> it failed, blowing he primary fuse.  Samlex was nice enough to send me a 
> .PDF file of the schematic.  Found the output switching transistors 
> (2SC3320) are both shorted.  No problem, they're readily available at 
> reasonable cost.  Over the past 60+ years I've repaired a gazillion 
> power supplies, but not a lot of experience with the switchers, hence 
> the question.
> 
> This unit has three 2200uF 25V Caps for filtering of the 12 Volt line. 
> Two in parallel right after the rectifier and a third after some filter 
> chokes.  The two parallel units are "bulging" at the top, it appears 
> that luck was with us and they didn't blow their guts all over the 
> inside of the unit.
> 
> My plans call to replace them along with the transistors, I'm just not 
> sure of one thing.  In a switching supply (runs at 25kHz), do I need to 
> order some special "Low ESR" 'lytics, or will everyday run of the mill 
> 2200uF 25Volt 'lytics do just fine???
> 

-- 
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Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
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