[time-nuts] HP 58503B PSU replacement

George Atkinson robertg8rpi at virginmedia.com
Wed Nov 14 18:12:32 EST 2018


Gerhard is correct, the supply Dave has needs a minimum of 500mA on the main output for correct operation according to the datasheet. I've not used this exact supply, but others ve used that had similar minimum load specificions would not run off-load. Typically thee lower limit is to put a bound on the size of storage inductor requred.

Per my first post use a 30VA 15V toroid, 7815, 7915 and switching 5V regulator.

Robert G8RPI.

> On 14 November 2018 at 18:12 Gerhard Hoffmann <dk4xp at arcor.de> wrote:
>
>
>
> Am 14.11.18 um 18:41 schrieb Dr. David Kirkby:
> > On Thu, 8 Nov 2018 at 21:43, Dr. David Kirkby <
> > drkirkby at kirkbymicrowave.co.uk> wrote:
> > On Thu, 8 Nov 2018, 14:53 George Atkinson via time-nuts <
> > time-nuts at lists.febo.com wrote:
> >>> Last month I was at the UK “National” hamfest and in the flea market area
> >>> a seller had a HP 58503B for sale. It was missing the cover and power
> >>> supply (AC mains version)including mounting. However it was only £3 (<5$)
> >>> so it was a no-brainer to buy it. Research shows that PSU failure is fairly
> >>> common on these units.
> >>>
> >>> I had the PSU fail in my 58503A. It keeps trying to start, then stops. I
> >>> have checked capacitors with an ESR meter, but could not fix it.
> >>>
> >>> Three is a good chance your unit takes the same PSU. If so
> >>>
> >>>
> >>> https://www.ebay.co.uk/itm/BEL-POWER-MAP55-4003-55W-Quad-Output-Embedded-Switch-Mode-Power-Supply-SMPS/132833037734
> >>>
> >>> may be of interest. I had an offer of £45 accepted yesterday.
> >>>
> >>> Dave.
> > Well, the bad news is the PSU I received was faulty (no output whatsoever),
> > and the seller has checked another, and that too is dead, so it looks like
> > he has rejects. He has refunded me and does not want the one he sent back.
> > So now I have two non-working supplies. The new one does not power up at
> > all. The old one does, but cycles on/off.
>
> If more than one replacement unit does not work, then it is not
>
> improbable that the switcher needs a minimum load to start.
>
>
> Also, a shorted capacitor can show excellent ESR.
>
>
> I once had a cycling power supply in a W&G TSA-2 spectrum analyzer.
>
> It delivered power for some seconds, and that was enough to trace
>
> a voltage to a faulty feedthrough capacitor. A DVM with enough digits
>
> helps a lot. Towards the short, the voltage sinks mV by mV.
>
>
> regards, Gerhard
>
>
>
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