[time-nuts] Fw: HP 105 powersupply problems

buehl buehl at superlink.net
Tue Apr 4 08:26:12 EDT 2006

Hello everyone:

Another method is to apply power for only 2-3 seconds; Much safer for 
switching supplies than low voltage.  This charges up the capacitors; If 
capacitors are leaking, there is no source of current to cause overheating 
or other failure modes.  The charge which remains on caps allows 
electrolytic barrier to "re-form".  Repeat this a dozen times over the 
course of a day.

Tom Buehl

At 03:23 AM 4/4/2006, Robert Atkinson wrote:
>Hi all,
>Using a Variac over a long period of time is great with conventional
>(Transformer-rectifier-capacitor) linear PSU's, but be careful with more
>modern equipment with switchmode PSU's. They can draw excessive current
>during undervoltage conditions.
>Still use your Variac, but ramp it up a little quicker, maybe 30s to a
>minute. Watch out for auto supply voltage (115/230) switch designs too,
>it's best not to cross the switching boundary too slowly as they may not
>switch back from voltage doubling to full-wave rectification resulting
>in very excessive internal voltages.
>If you don't have a Variac, try a low wattage (40W) light bulb in series
>with the supply to limit the current.
>Robert G8RPI.
>-----Original Message-----
>From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>Behalf Of Poul-Henning Kamp
>Sent: 04 April 2006 06:28
>To: Discussion of precise time and frequency measurement
>Subject: Re: [time-nuts] Fw: HP 105 powersupply problems
>In message <002901c6578c$9d928120$0e8fae43 at hsd1.in.comcast.net>,
>"Richard and M
>arcia Putz" writes:
> >I had similar problems with my HP105, not bad transistors, check
> >out the filter capacitors. Electrolytics in any equipment past 15-20
> >years of age could be suspect. I'd look there first.
>In general when powering up equipment that has been turned of for
>years:  Use a variac and ram the voltage up slowly over a couple of
>Electrolytics can loose their polarisation over time and if exposed
>to full voltage they are likely to splatter all over the place, but
>if you give them a slow start they will most often recover their
>polarisation and work fine.
>Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>phk at FreeBSD.ORG         | TCP/IP since RFC 956
>FreeBSD committer       | BSD since 4.3-tahoe
>Never attribute to malice what can adequately be explained by
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