Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Replacing Large Electrolytics

On 8/28/18 4:15 AM, Cursitor Doom wrote:
If you're a professional repair tech, I can see why you would
only use new parts. But I'm just a ham; a hobbyist. And we
hams have been successfully reforming electros for many decades
without any adverse outcomes. Loads of info on the net it you
care to look for it, but I'm guessing since you're a pro you'll
turn your nose up at the very thought!


Hams are notoriously cheap.
And the internet is a cesspool of useless information.

I've been a licensed Ham for 50 years now.
You wouldn't believe some of the butchery I've encountered on
Ham radio gear. I have a phrase for it. Joe "Claw Hammer" Ham
has been here. Apparently having a ham license gives you the
ability to think you know more than any commercial engineer.

That being said, I've used old NOS capacitors for myself.
But I don't waste my time reforming them. They either work right
the first time they have power applied or they don't.


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if there is room, just leave the old cap in place and wire a new one in parallel.

m


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In article ,
says...

Hams are notoriously cheap.
And the internet is a cesspool of useless information.

I've been a licensed Ham for 50 years now.
You wouldn't believe some of the butchery I've encountered on
Ham radio gear. I have a phrase for it. Joe "Claw Hammer" Ham
has been here. Apparently having a ham license gives you the
ability to think you know more than any commercial engineer.

That being said, I've used old NOS capacitors for myself.
But I don't waste my time reforming them. They either work right
the first time they have power applied or they don't.



I understand that # 40 wire was made by 2 hams arguing over a penny.

I have only been a ham for 45 years. I like you have seen many things
cobbled together. Have even done some of that myself. Not that I
thought I was a better engineer,but because I only had so much money to
do things. Those were projects for myself.

If I am doing things for myself, I may do anything to get equipment
going. If I were doing things for others, it would be with good parts.
Like the time at work an outside repair person came in to repair a 3
phase motor drive unit. He found 2 out of 3 diodes bad. I told him to
replace the 3 rd one. It may have been under stress or not. He said
they were $ 200 each. Told him it costs us $ 1000 or more per hour
while that equipment was down, so $ 200 is good insurance it will not
quit in a short time.
That 3 rd diode would probably last , but why take a chance at those
rates.

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On Tuesday, August 28, 2018 at 9:43:42 AM UTC-4, wrote:
if there is room, just leave the old cap in place and wire a new one in parallel.

m


And when the old one fails short?

Peter Wieck
Melrose Park, PA


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On Tue, 28 Aug 2018 11:07:13 -0400, Ralph Mowery wrote:

If I am doing things for myself, I may do anything to get equipment
going. If I were doing things for others, it would be with good parts.
Like the time at work an outside repair person came in to repair a 3
phase motor drive unit. He found 2 out of 3 diodes bad. I told him to
replace the 3 rd one. It may have been under stress or not. He said
they were $ 200 each. Told him it costs us $ 1000 or more per hour
while that equipment was down, so $ 200 is good insurance it will not
quit in a short time.
That 3 rd diode would probably last , but why take a chance at those
rates.


And that is the very core of this issue: economics. As a hobbyist, I'm
only fixing up my own stuff and if it goes wrong again in a couple of
years owing to the NOS parts I used having failed - I don't believe they
will for a moment but simply for the sake of argument - then it's no big
deal at all for me.
It's a totally different story for professional repairers who would be
foolish indeed to install anything other than good quality new parts from
a reputable supplier. Sure it costs more, but for a pro, it's well worth
it for all sorts of reasons.



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On Wed, 22 Aug 2018 04:03:23 -0700, tabbypurr wrote:

Sounds about par for the course. Go back further to paper caps and it'd
be a surprise to find any still working properly. And yes, micamold were
paper caps.


I've got a box full of the oil & paper caps that come in cubiod cans and
they all tested fine (I have an awful lot of vintage spares here). Not so
sure about the tubular paper caps which I assume you're talking about,
though.





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On Tuesday, August 28, 2018 at 10:54:07 AM UTC-7, Gunther Heiko Hagen wrote:
On Mon, 27 Aug 2018 14:02:45 -0700, wrote:
On Monday, August 27, 2018 at 12:50:00 PM UTC-7, Terry Schwartz wrote:
...Spend the $25 and get new parts...

Here in Silicon Valley, it would be a lot less. 4700uF/35V and
5600uF/42V are both available at retail for under US$1 each.


Can you kindly provide a link to the supplier you refer to who's able to
offer such truly extraordinary prices?

Anchor Electronics, 2040 Walsh Avenue, Santa Clara, California 95050 USA
http://www.anchor-electronics.com/

https://anchor-electronics.com/price-list.pdf

Electrolytic capacitors are on page 13.

I am a retail, over-the-counter customer. I do not know about their mail order policies, except the last page of the price list says "We Ship To USA & Canada Addresses Only."
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On Tue, 28 Aug 2018 14:14:36 -0700, wrote:

Anchor Electronics, 2040 Walsh Avenue, Santa Clara, California 95050
USA
http://www.anchor-electronics.com/

https://anchor-electronics.com/price-list.pdf

Electrolytic capacitors are on page 13.

I am a retail, over-the-counter customer. I do not know about their
mail order policies, except the last page of the price list says "We
Ship To USA & Canada Addresses Only."


Very interesting.... many thanks for that.



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On 08/28/2018 01:47 PM, Cursitor Doom wrote:
On Wed, 22 Aug 2018 04:03:23 -0700, tabbypurr wrote:

Sounds about par for the course. Go back further to paper caps and it'd
be a surprise to find any still working properly. And yes, micamold were
paper caps.


I've got a box full of the oil & paper caps that come in cubiod cans and
they all tested fine (I have an awful lot of vintage spares here). Not so
sure about the tubular paper caps which I assume you're talking about,
though.


Moisture + acid paper + foil = mess. That'll take a lot longer if the
cap has metal on five sides.

Cheers

Phil Hobbs


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Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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On Saturday, 1 September 2018 20:48:34 UTC+1, Phil Hobbs wrote:
On 08/28/2018 01:47 PM, Cursitor Doom wrote:
On Wed, 22 Aug 2018 04:03:23 -0700, tabbypurr wrote:

Sounds about par for the course. Go back further to paper caps and it'd
be a surprise to find any still working properly. And yes, micamold were
paper caps.


I've got a box full of the oil & paper caps that come in cubiod cans and
they all tested fine (I have an awful lot of vintage spares here). Not so
sure about the tubular paper caps which I assume you're talking about,
though.


Moisture + acid paper + foil = mess. That'll take a lot longer if the
cap has metal on five sides.

Cheers

Phil Hobbs


My prewar metal can paper caps are all wax sealed, and every last one tested dead as a very dead thing. The non-metal seal is where it can go wrong. Not sure why they didn't use bitumen.


NT
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On Friday, August 24, 2018 at 10:35:43 PM UTC-7, Fox's Mercantile wrote:
On 8/24/18 6:42 PM, Cursitor Doom wrote:
I had 3 faulty electrolytics; all 30V/5500uF. In my spares bin I found 6
NOS (new old stock) electros ...
These spares, though unused, are probably 40 years old. Will they need re-
forming gradually over 24hrs before installing?


Reforming is a fool's game.
They either work to being with or they're bad.


That's not ny experience; yes, I might toss the 40--year-olds, but only
because new ones are cheap and probably better performing.
Even one-year-old capacitors can benefit from reforming, though,
and for some uses (timing capacitors) it's beneficial.

It doesn't take 24 hours, though: with a current-limited supply, just
give 'em 150% of the rated voltage and warm 'em with a hair
dryer for a few minutes, while watching the leakage current.
You can see it drop from milliamps to microamps.
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On 9/2/18 3:15 AM, whit3rd wrote:
It doesn't take 24 hours, though: with a current-limited supply, just
give 'em 150% of the rated voltage and warm 'em with a hair
dryer for a few minutes, while watching the leakage current.
You can see it drop from milliamps to microamps.


That's not how manufacturing does it.
Their installed and at the end of assembly line, full power is applied.
They either work or they don't.



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On Sun, 2 Sep 2018 06:03:04 -0500, Fox's Mercantile
wrote:

On 9/2/18 3:15 AM, whit3rd wrote:
It doesn't take 24 hours, though: with a current-limited supply, just
give 'em 150% of the rated voltage and warm 'em with a hair
dryer for a few minutes, while watching the leakage current.
You can see it drop from milliamps to microamps.


That's not how manufacturing does it.
Their installed and at the end of assembly line, full power is applied.
They either work or they don't.


I remember when part of my job was fixing power supplies. Some that
failed the automatic part of the test last thing on one day would work
the day after.

I never found out why that happened but I assumed it was an
electrolytic so I changed the lot.

Steve

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http://www.npsnn.com



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On Sun, 02 Sep 2018 06:03:04 -0500, Fox's Mercantile wrote:

That's not how manufacturing does it.
Their installed and at the end of assembly line, full power is applied.
They either work or they don't.


That's all very well for *brand new* capacitors!





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On 2018-08-28 10:47, Cursitor Doom wrote:
On Wed, 22 Aug 2018 04:03:23 -0700, tabbypurr wrote:

I've got a box full of the oil & paper caps that come in cubiod cans and
they all tested fine (I have an awful lot of vintage spares here).


Enjoy your PCBs.

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On Sunday, 2 September 2018 20:38:38 UTC+1, +++ATH0 wrote:
On 2018-08-28 10:47, Cursitor Doom wrote:


I've got a box full of the oil & paper caps that come in cubiod cans and
they all tested fine (I have an awful lot of vintage spares here).


Enjoy your PCBs.


and not the good type


NT
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On Sunday, September 2, 2018 at 4:45:44 AM UTC-7, Stephen Wolstenholme wrote:
On Sun, 2 Sep 2018 06:03:04 -0500, Fox's Mercantile
wrote:


[about electrolytic capacitors]

Their installed and at the end of assembly line, full power is applied.
They either work or they don't.


I remember when part of my job was fixing power supplies. Some that
failed the automatic part of the test last thing on one day would work
the day after.

I never found out why that happened but I assumed it was an
electrolytic so I changed the lot.


Electrolytics have to be formed (kept under bias for a period) before they
develop the dielectric (oxide) layer, AND that layer is continuously
renewed when they're under bias. On the shelf, however, it degrades.
Some switchmode power supplies (the old Apple II types) rely on
timing capacitors for startup sequencing, and the power filter electrolytics are
NOT the prime suspects when such a power supply doesn't work.

You can often fix those power supplies by leaving 'em turned on overnight.
The most plausible reason for this is that the timing capacitors (not the big
filter caps) have to be re-formed. This syndrome can't be improved with
new filter capacitors (I've tried). Once they work, they're reliable again.


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Once upon a time on usenet John Robertson wrote:
On 2018/08/25 11:23 AM, Cursitor Doom wrote:
On Sat, 25 Aug 2018 10:39:13 -0700, John-Del wrote:

Heat and charge cycles do affect a capacitor's life, but they're
not the only factors. Humans who smoke, drink, and do drugs have a
shorter life than those who don't, but we all will die eventually.


Hmmm. Not really a valid analogy!

I've had plenty of electros in stock go off value, become leaky,
and go up in ESR just from sitting in a nice quiet bin. I don't
install any cap without running through my Z meter, and I will toss
an entire lot of caps if one is bad.


I managed to find 8 electros in my bin that could used in parallel
to get the equivalent of the failed ones I've removed. I've checked
them all for ESR, leakage and Capacitance and the readings I've got
have come out indistinguishable from new caps of the same value &
voltage rating. I've picked the best 6 (with the lowest ESR) and am
re-forming them over the course of this weekend.
I'll report back in due course on the success (or failure) of this
method. I certainly wouldn't want to hit them with their rated
voltage straight away after so long in limbo as that *would* be
inviting disaster.


The final test is leakage, set the cap up with an ammeter in series
and put it on a power supply running around 75% of the rated maximum
voltage. Leakage should be very low after the cap has stabilized.

Here is a nice write-up:

https://www.nmr.mgh.harvard.edu/~reese/electrolytics/

Heathkit made a great cap checker that we use to check older off the
shelf NOS caps. Has the Magic-Eye tube and everything - except ESR.


Thanks for that link.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)


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