[Boatanchors] 'Stoopid' OT question

[Michael Clarson]

I used to go by the old switching supply saying -- you can't troubleshoot
them until you fix them..Now I just shotgun likely parts so I do not have
to open it up again.  I had two Samlux 1223s. Same symptom: Blew fuses. One
had shorted output transistors, and the other had only one blown
transistor, and the thermistor got so hot it melted the solder and fell off
the board after it burned in half. Both had bulging caps. I replaced the
caps with higher temp units (105 deg, I believe). No problems since..
--Mike, WV2ZOW

On Fri, Aug 11, 2017 at 10:30 PM, Phil <ko6bb1 at gmail.com> 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???
>
> --
> 73 From "The Beaconeer's Lair"
> Specializing in DXing NDBs (Longwave Beacons)
> Phil, KO6BB,  http://www.qsl.net/ko6bb/
> KO6BB/B beacon, ~20W on 28.290 MHz, Ringo Vertical
>
> HF/LF RADIOS:
> HOMEBREW:   7 Tube+Rect 1v3 Regen RX for LF (built 2015)
> Icom:       IC-7200 Xceiver, DSP IF & filters (~2015).
> Kenwood:    TS-450SAT Xceiver, cascaded 250/125Hz Inrad filters.
> 10M Beacon: 2 x Realistic HTX-100's on 28.290MHz
> SDR:        Softrock Ensemble II LF (built from a kit 2017).
>
> ACC:   HOMEBREW  LF-MF Pre-Amp, 8Hz Audio Filter.
>        HOMEBREW  4 Port Antenna Multicoupler, Feeds 4 RX's.
>        ANTENNAS: 88 foot Long Ladder-line fed dipole, 35 feet AGL for
> MW/SW.
>           Active Mini-Whip, 36 Feet AGL for LF/MW/SW.
>           37 foot "Low Noise Vertical", 11 feet AGL for LF/MW/SW.
>           Cushcraft AR-10 Ringo Vertical, 14 feet AGL for 10M beacon.
> Merced, Central California, 37, 18, 37N   120, 30, 6W CM97rh
>
>
> ---
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