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Old 23rd May 2019, 8:48 pm   #1
Andrewausfa
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Default Farnell power supply electrolytics

Could I recommend to owners of Farnell L series bench power supplies that they check under the bonnet This is a 1972/73 L30DT I picked up recently and the second one I've seen like this. All four cans have vented and two were that bad they've sprayed the rear panel in electrolyte. Very nice units to service anyway, with the exception of the rivets holding the capacitor can clamps in place.

Andrew
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Old 23rd May 2019, 9:05 pm   #2
Herald1360
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Default Re: Farnell power supply electrolytics

The wiring layout to the big cans looks dodgy- common in/out wiring resistance in the ripple loop seems to be the case. Probably not noticeable with a decent regulator downstream but still.......
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Old 23rd May 2019, 9:09 pm   #3
Andrewausfa
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Default Re: Farnell power supply electrolytics

Hi Chris,

That's the way they come

Andrew
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Old 23rd May 2019, 11:09 pm   #4
Refugee
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Default Re: Farnell power supply electrolytics

I caught a set of the high ripple version in something else just before the electrolyte began to seep out.
Several thick coats of varnish over the rubber bungs appears to have worked.
Once some electrolyte has got out it is unlikely they will recover.
I tried re-hydrating one and found that the rubber had gone so far that it was conductive. The trial was done on a 450V capacitor.
Lower voltage types might fare better.
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Old 23rd May 2019, 11:49 pm   #5
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Default Re: Farnell power supply electrolytics

Those are nasty. I had a couple of those ruin the power supply in a Telequipment scope. Lose 'em quick.
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Old 24th May 2019, 9:45 am   #6
Andrewausfa
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Default Re: Farnell power supply electrolytics

Yes very nasty! There must have been quite some pressure building up in them. Interesting to see how they have vented, the two on the right seem to have been bubbling and sputtering away while the two on the left look like they have completely discharged their liquid contents in one go.

I guess, like many of these units coming out of scientific (as this one has) or educational establishments, it's seen a bit of use. As I say, this is the second one I've seen with vented capacitors in.

Anyway, the current incumbents are in process of being ejected and replaced, hence me having to drill out the can clamp rivets to put new 30mm clamps in.

Andrew
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Old 25th May 2019, 10:55 am   #7
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Default Re: Farnell power supply electrolytics

My unit has the big 'terry' clips, and I think I posted on here before that the clips were held down with pop rivets. These were too long, had been inserted from underneath, and one had pierced the blue plastic film causing the right channel floating -ve connection to be clamped to ground. I had it for decades before this caused a problem one day.
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Old 26th May 2019, 7:39 pm   #8
ColinTheAmpMan1
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Default Re: Farnell power supply electrolytics

I have two of these Farnell PSUs; a single L30B (30VDC, 1A: S/N 002268) and a dual L30DT (two 30VDC, 2A: S/N 000841). I have checked them and the capacitors are fine. The question is, are mine younger or older than the ones with the leaking capacitors?

Colin.
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