[time-nuts] HP 58503B PSU replacement

[George Atkinson via time-nuts]

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. There does not even seem to be an assembly level service manual readily available for the 58503B never mind a CLIP. I could not identify the power supply used but assumed it was a standard 3rd party SMSU. Connecting up to a triple output bench PSU (+5V, +15V -15V) and antenna and the unit powered up and locked. Checking he fault log confirmed that the PSU had failed with voltage out of range. I measured the current on the supplies and surprisingly the current on the -15 supply was the highest during warm-up at around 750mA. Once warmed up the -15V current fell and +15V current went up. Unfortunately all the 30- 40W SMPSUs (the 58503B is rated t 35W max input) I had handy had significantly lower -15V supply current ratings. I decided to build a mostly linear supply. The basis was a dual secondary 15V toroidal transformer, two full wave bridge rectifiers, 7815 and 7915 regulators and a switching “7805” replacement for +5V. Calculations for a 30VA transformer show that the winding for the negative regulator would be slightly overloaded during oven warm-up however the “positive” winding will be well under loaded at this point because the +15V current is low. So saturation is not an issue and the total I2R heating is less than for full rated load on both windings. So I knocked this up with a 30VA toroid, an a 194mm x 90mm alloy plate and a couple of bits of extruded angle to pick- up on the existing locations. A 20mm fuse holder was added to an existing hole in the back panel. A cover for a 53131A was bought on ebay for $20 (I was in the USA for 10 days so got it delivered to my hotel so postage was cheap). So it all worked fine but the GPS week roller-over bug was there. Lady Heater corrects this but I had some other Oncore timing receivers about so I tried a VP and it gives the correct date and operation. I have another GPSDO for under $50.
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[Mark Sims]

I put a $25 50 watt (?) Meanwell in mine and in mine and it works well. The original power supply was made by PowerOne. They are still made...$300-$400 on Digikey and Mouser.

My 58503B had a shorted ceramic cap across the input of one of the 15V regulators. The cap was glowing orange with the new supply. Maybe that killed the original supply.

I think the OCXO oven heater is powered across across +/- 15V.
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[Dr. David Kirkby]

On Thu, 8 Nov 2018, 14:53 George Atkinson via time-nuts <

Post by George Atkinson via time-nuts
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.

Those power supplies can often be found up to £300 on eBay, but Arrow
Electronics sells them new at £120.


Dave.
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[George Atkinson via time-nuts]

Hi Dave,
Thanks for the info. I've already built the analogue supply and it's working fine. It's interesting that even that 55W supply is operating near it's -15V limit with the 58503A and the minumum load requiremen on th main +5V rail is not quite met either.

Robert.

Post by George Atkinson via time-nuts
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.
Those power supplies can often be found up to £300 on eBay, but Arrow Electronics sells them new at £120.
Dave.

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[Dr. David Kirkby]

hOn Fri, 9 Nov 2018, 13:49 George Atkinson via time-nuts <

Post by George Atkinson via time-nuts
Hi Dave,
Thanks for the info. I've already built the analogue supply and it's
working fine. It's interesting that even that 55W supply is operating near
it's -15V limit with the 58503A and the minumum load requiremen on th main
+5V rail is not quite met either.
Robert.

Thank you Robert. I will check the 5 V load and add a bit of extra load if
needed.

I will also look at adding a bit more heatsinking.

I prefer linear supplies - I know how to fix them when they go wrong. I do
not get on too well with switch mode supplies.

Dave
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[Dr. David Kirkby]

On Thu, 8 Nov 2018 at 21:43, Dr. David Kirkby <

Post by Dr. David Kirkby
On Thu, 8 Nov 2018, 14:53 George Atkinson via time-nuts <

Post by George Atkinson via time-nuts
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.
--
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892
https://www.kirkbymicrowave.co.uk/
Tel [phone]
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[Gerhard Hoffmann]

Post by Dr. David Kirkby
On Thu, 8 Nov 2018 at 21:43, Dr. David Kirkby <
On Thu, 8 Nov 2018, 14:53 George Atkinson via time-nuts <

Post by George Atkinson via time-nuts
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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[George Atkinson via time-nuts]

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.

Post by Gerhard Hoffmann

Post by Dr. David Kirkby
On Thu, 8 Nov 2018 at 21:43, Dr. David Kirkby <
On Thu, 8 Nov 2018, 14:53 George Atkinson via time-nuts <

Post by George Atkinson via time-nuts
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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[Dr. David Kirkby]

Post by Gerhard Hoffmann
If more than one replacement unit does not work, then it is not
improbable that the switcher needs a minimum load to start.

There is a minimum load specified on the 5 V rail, and someone wrote above
that the GPS receiver does not meet that requirement.

I tested my supply in the GPS receiver, but it may be worth having another
go while definitely meeting the load requirements.

Post by Gerhard Hoffmann
Also, a shorted capacitor can show excellent ESR.

Luckily I have a Peak ESR70 ESR/Capacitance meter.

Post by Gerhard Hoffmann
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.

One of the problems with this PSU is a lot of components are glued
together. It is almost impossible to see if some tracks belong to a
capacitor or not.

The board layout leaves a lot to be desired. There are components mounted
about 45 degrees to the board to fit them in.

Post by Gerhard Hoffmann
regards, Gerhard..

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