[time-nuts] Re: Power supply buzzing in HP 58503A GPS receiver.

[Ed Marciniak]

I don’t have one of those units, but switching power supplies under certain load conditions can have subharmonic oscillations that happen to fall in the audible frequency range. Absent an overload from a shorter capacitor or similar, I’d take a hard look at whether there are capacitors that no longer meet their ESR specifications and/or have cold solder joints effectively removing them from the circuit.
________________________________
From: Wilko Bulte via time-nuts <time-nuts at lists.febo.com>
Sent: Sunday, September 10, 2023 3:57:06 PM
To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Wilko Bulte <wkb at xs4all.nl>
Subject: [time-nuts] Re: Power supply buzzing in HP 58503A GPS receiver.

Wild guess here, this sounds to me like a coil "whistling". Maybe there is an inductor or transformer  that lost its potting compound, or has somehow come loose from its fittings?

best,
Wilko

> On 10 Sep 2023, at 21:24, David Kirkby via time-nuts <time-nuts at lists.febo.com> wrote:
>
> After about 6 months of being powered off, I switched on my GPS receiver
> yesterday. The PSU is buzzing quite loudly. Sound file at
>
> https://www.kirkbymicrowave.co.uk/noisy-PSU-in-HP-58503A-GPS-time-and-frequency-standard-recorded-10th-Sempember-2023.m4a
>
> I thought that one of the 100 uF 400 V capacitors after the rectifier might
> be bulging, although I was unsure. The capacitance measures okay, and the
> ESR is below that of anything I can buy that will physically fit. Same for
> the 47 uF 400 V capacitor. These were both measured out of circuit, using
> an HP 4284A LCR meter at 120 Hz. I chose that, despite the fact that we
> have 50 Hz mains here in the UK, as data normally seems to be provided on
> capacitors at 120 Hz.
>
> Has anyone experienced this before? I believe that someone wrote here, or
> might have been elsewhere, that the GPS receiver was pushing one of the
> supplies to the limit, and another one was not loaded enough. I know there
> was some mention of converting it to run from a linear supply, although I
> think that would be physically larger, so not fit in the case.
>
>
> --
> Dr David Kirkby Ph.D
> Kirkby Microwave Ltd
> Email: drkirkby at kirkbymicrowave.co.uk
> Web: https://www.kirkbymicrowave.co.uk/
> Telephone 07910 441670 (UK) or +44 7910 441670 (international)
> Registered in England and Wales, company number 08914892.
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT
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