.... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a constant
background hum. (http://www.kef.com/history/2000/subwoofers/sub2.asp)

Pretty sure it's just a mains frequency hum coming from its power supply (it
doesn't change whether any input is connected or not).

Does this sound like a fairly basic/simple repair job? Is it likely to be
just the smoothing capacitors in the power supply or might it be more
complicated?

I know which end of a soldering iron to hold and recognise the dangers of
big capacitors. Could I fix it myself?

Tim

Tim Downie wrote:
... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a constant
background hum. (http://www.kef.com/history/2000/subwoofers/sub2.asp)

Pretty sure it's just a mains frequency hum coming from its power supply (it
doesn't change whether any input is connected or not).

Does this sound like a fairly basic/simple repair job? Is it likely to be
just the smoothing capacitors in the power supply or might it be more
complicated?

I know which end of a soldering iron to hold and recognise the dangers of
big capacitors. Could I fix it myself?

Tim


Is it a gritty him or a fairly 100zh hum or a really 50hz hum..

I am surprised..how long has it been doing it, and how long have you had it?

You MIGHT have an earth loop.. unplug it and see whether the audio
input earth is connected to the mains earth.(use a continuity tester).if
so try a quick test with the mains earth disconnected...

Tim Downie wrote:

... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a constant
background hum. (http://www.kef.com/history/2000/subwoofers/sub2.asp)

Pretty sure it's just a mains frequency hum coming from its power supply (it
doesn't change whether any input is connected or not).

It could be a problem with the unit, or it could lay outside... I had
similar problems with my surround system picking up hum. In the end I
managed to eliminate it by the simple expedient of changing the socket
it was all powered from! (nothing immediately obviously wrong with the
socket either - although we are on a TT system, so getting a good earth
reference is not easy). Perhaps some experimentation with wire routing,
power outlets etc may be worth while before getting too deeply into the
insides of the sub.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The Natural Philosopher wrote:
Tim Downie wrote:
... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a
constant background hum.
(http://www.kef.com/history/2000/subwoofers/sub2.asp) Pretty sure it's
just a mains frequency hum coming from its power
supply (it doesn't change whether any input is connected or not).

Does this sound like a fairly basic/simple repair job? Is it likely
to be just the smoothing capacitors in the power supply or might it
be more complicated?

I know which end of a soldering iron to hold and recognise the
dangers of big capacitors. Could I fix it myself?

Tim


Is it a gritty him or a fairly 100zh hum or a really 50hz hum..

I'm pretty sure it's 50 hz. I thought somesome somewhere would have
recorded mains hum on the net for comparison but I haven't found it yet.


I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.


You MIGHT have an earth loop.. unplug it and see whether the audio
input earth is connected to the mains earth.(use a continuity
tester).if so try a quick test with the mains earth disconnected...

Don't think so. Doesn't matter where in the house I plug it in and nothing
has changed with regards to its wiring in donkey's years. I'll get the
multimeter out after I've walked the dogs.

Tim

HI Tim

On Tue, 6 Mar 2007 08:35:55 -0000, "Tim Downie"
wrote:

The Natural Philosopher wrote:
Tim Downie wrote:
... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a
constant background hum.
(http://www.kef.com/history/2000/subwoofers/sub2.asp) Pretty sure it's
just a mains frequency hum coming from its power
supply (it doesn't change whether any input is connected or not).

Does this sound like a fairly basic/simple repair job? Is it likely
to be just the smoothing capacitors in the power supply or might it
be more complicated?

I know which end of a soldering iron to hold and recognise the
dangers of big capacitors. Could I fix it myself?

Tim


Is it a gritty him or a fairly 100zh hum or a really 50hz hum..

I'm pretty sure it's 50 hz. I thought somesome somewhere would have
recorded mains hum on the net for comparison but I haven't found it yet.

There's (allegedly) a sample of 50hz hum in Wikipedia
en.wikipedia.org/wiki/Mains_hum





I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.

Now that sounds like one or more large electrolytic caps slowly drying
out.....? As they dry out their capacitance decreases, and their
effectiveness at 'smoothing' decreases.....

Should be fairly obvious which the culprits are (assuming it's a
transformer-type 'linear' power supply). If you can identify the
culprits, then you should be able to find replacements from the usual
suspects....

To confim the diagnosis you could try adding a couple of
(suitably-rated) caps across the suspected duff caps on short plying
leads - taking due care to safely discharge the stored energy, which,
athough it's _probably_ not lethal g might well make you jump, or
even weld your screwdriver to something ! BTDT !

Hope this helps

Adrian

In article ,
Tim Downie wrote:
I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.

First call would be the main smoothing caps.

--
*24 hours in a day ... 24 beers in a case ... coincidence? *

Dave Plowman London SW
To e-mail, change noise into sound.

Tim Downie wrote:
The Natural Philosopher wrote:
Tim Downie wrote:
... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a
constant background hum.
(http://www.kef.com/history/2000/subwoofers/sub2.asp) Pretty sure it's
just a mains frequency hum coming from its power
supply (it doesn't change whether any input is connected or not).

Does this sound like a fairly basic/simple repair job? Is it likely
to be just the smoothing capacitors in the power supply or might it
be more complicated?

I know which end of a soldering iron to hold and recognise the
dangers of big capacitors. Could I fix it myself?

Tim


Is it a gritty him or a fairly 100zh hum or a really 50hz hum..

I'm pretty sure it's 50 hz. I thought somesome somewhere would have
recorded mains hum on the net for comparison but I haven't found it yet.


Its probably 100hz.

I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.

Ok. Its possible that the main capacitors are going high impedance-ish

It's also possible that as components are ageing its power supply
rejection is worsening.



You MIGHT have an earth loop.. unplug it and see whether the audio
input earth is connected to the mains earth.(use a continuity
tester).if so try a quick test with the mains earth disconnected...

Don't think so. Doesn't matter where in the house I plug it in and nothing
has changed with regards to its wiring in donkey's years. I'll get the
multimeter out after I've walked the dogs.


Ok, thats ruled out..

Check first by switching it off while running..there should be a few
seconds of power ..if the hum vanishes as soon as the PSU is off the
mains, but it still works, its definitely self generated.



Tim

"John Rumm" wrote in message
...
Tim Downie wrote:

... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a constant
background hum. (http://www.kef.com/history/2000/subwoofers/sub2.asp)

Pretty sure it's just a mains frequency hum coming from its power supply
(it doesn't change whether any input is connected or not).

It could be a problem with the unit, or it could lay outside... I had
similar problems with my surround system picking up hum. In the end I
managed to eliminate it by the simple expedient of changing the socket it
was all powered from! (nothing immediately obviously wrong with the socket
either - although we are on a TT system, so getting a good earth reference
is not easy). Perhaps some experimentation with wire routing, power
outlets etc may be worth while before getting too deeply into the insides
of the sub.

All the responses so far have assumed an amplified hum signal. This unit has
a built in amplifier and it's possible the mains transformer for the power
supply is physically humming/vibrating as it is loose or has become so and
it's nothing to do with leads, connections etc. This would sound like it was
coming out of the speaker.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Bob Mannix wrote:
"John Rumm" wrote in message
...
Tim Downie wrote:

... and no, it's not because it can't remember the words. ;-)

All the time my KEF PSW2000 subwoofer is powered up, there is a constant
background hum. (http://www.kef.com/history/2000/subwoofers/sub2.asp)

Pretty sure it's just a mains frequency hum coming from its power supply
(it doesn't change whether any input is connected or not).
It could be a problem with the unit, or it could lay outside... I had
similar problems with my surround system picking up hum. In the end I
managed to eliminate it by the simple expedient of changing the socket it
was all powered from! (nothing immediately obviously wrong with the socket
either - although we are on a TT system, so getting a good earth reference
is not easy). Perhaps some experimentation with wire routing, power
outlets etc may be worth while before getting too deeply into the insides
of the sub.

All the responses so far have assumed an amplified hum signal. This unit has
a built in amplifier and it's possible the mains transformer for the power
supply is physically humming/vibrating as it is loose or has become so and
it's nothing to do with leads, connections etc. This would sound like it was
coming out of the speaker.


That is entirely possible. Though quality kit will generally use a
toroid that should not be too bad in that respect.

Tim Downie wrote:

All the time my KEF PSW2000 subwoofer is powered up, there is a constant
background hum.


3 likely options are
- bad psu reservoir lytics
- bad capacitor connected to the amp IC that helps it reject psu hash
- a worsening poor connection on a ground wire somewhere in the unit
- mechanical transformer hum is also possible, but far less common
than the others.

Capacitors can be piggybacked to check them
Bad connections can be pressed/prooded to check them


NT

In article ,
Bob Mannix wrote:
All the responses so far have assumed an amplified hum signal. This unit
has a built in amplifier and it's possible the mains transformer for
the power supply is physically humming/vibrating as it is loose or has
become so and it's nothing to do with leads, connections etc. This
would sound like it was coming out of the speaker.

In this context they don't usually produce 50Hz but more of a buzz. They
can produce low frequencies when attached to a large resonant panel but
I'd say a speaker maker would avoid this.

--
*A conclusion is the place where you got tired of thinking *

Dave Plowman London SW
To e-mail, change noise into sound.

Tim Downie wrote:

I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.

Ah, that does change the probably cause a bit... I would have to go
along with dodgy smoothing cap as well (the time frame would also
possibly coincide with a period when a large number of duff
electrolytics were made, many of which started going tits up after a
couple of years.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The Natural Philosopher wrote:

Check first by switching it off while running..there should be a few
seconds of power ..if the hum vanishes as soon as the PSU is off the
mains, but it still works, its definitely self generated.

Yep. Hum stops as soon mains cut.

Tim

John Rumm wrote:
Tim Downie wrote:

I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.

Ah, that does change the probably cause a bit... I would have to go
along with dodgy smoothing cap as well (the time frame would also
possibly coincide with a period when a large number of duff
electrolytics were made, many of which started going tits up after a
couple of years.

Next question, where's a good place to buy replacements?

Before you say "RS" or "MAPLIN", neither of them seem to stock capacitors
with the same spec.

The present ones were made by Licon. 12000 microfarads, 63V. On the other
side they say LSM, 85C(M), VENT.

Terminals seem to be two pins that pass through pcb. (Don't know the spacing
yet). Overall package about 34mm diameter & 46mm high.

How crucial is it to replace like with like? 12,000 seems to be an odd
value. Most catalogues that I've looked at so far list 10,000 & 15,000
microfarad capacitors but not 12,000. Is there any harm in "over-specing"
slightly?

Tim

The Natural Philosopher wrote:
Bob Mannix wrote:

All the responses so far have assumed an amplified hum signal. This
unit has a built in amplifier and it's possible the mains
transformer for the power supply is physically humming/vibrating as
it is loose or has become so and it's nothing to do with leads,
connections etc. This would sound like it was coming out of the
speaker.
That is entirely possible. Though quality kit will generally use a
toroid that should not be too bad in that respect.

It is a toroid. Is it safe to power it up with the speaker disconnected to
check that it's not coming from the transformer?

Tim

"Tim Downie" wrote in message
...
John Rumm wrote:
Tim Downie wrote:

I am surprised..how long has it been doing it, and how long have you
had it?

Had the sub for 5-6 years now. Hum has slowly been getting worse.

Ah, that does change the probably cause a bit... I would have to go
along with dodgy smoothing cap as well (the time frame would also
possibly coincide with a period when a large number of duff
electrolytics were made, many of which started going tits up after a
couple of years.

Next question, where's a good place to buy replacements?

Before you say "RS" or "MAPLIN", neither of them seem to stock capacitors
with the same spec.

The present ones were made by Licon. 12000 microfarads, 63V. On the
other
side they say LSM, 85C(M), VENT.

Terminals seem to be two pins that pass through pcb. (Don't know the
spacing
yet). Overall package about 34mm diameter & 46mm high.

How crucial is it to replace like with like? 12,000 seems to be an odd
value. Most catalogues that I've looked at so far list 10,000 & 15,000
microfarad capacitors but not 12,000. Is there any harm in "over-specing"
slightly?

Tim

I would not worry about replacing like with like, just get some caps that
will physically fit and are at least 12 mFds. 15mFd is fine. I would like to
know, however, why they failed after only 5-6 years. If I were doing this, I
would try and get some high-temperature capacitors which hopefully won't
fail so quickly.

S.

The Natural Philosopher wrote:

Check first by switching it off while running..there should be a few
seconds of power ..if the hum vanishes as soon as the PSU is off the
mains, but it still works, its definitely self generated.

Yep. Hum stops as soon mains cut.

Tim

Tim Downie wrote:
John Rumm wrote:
Tim Downie wrote:

I am surprised..how long has it been doing it, and how long have you
had it?
Had the sub for 5-6 years now. Hum has slowly been getting worse.
Ah, that does change the probably cause a bit... I would have to go
along with dodgy smoothing cap as well (the time frame would also
possibly coincide with a period when a large number of duff
electrolytics were made, many of which started going tits up after a
couple of years.

Next question, where's a good place to buy replacements?

Before you say "RS" or "MAPLIN", neither of them seem to stock capacitors
with the same spec.

The present ones were made by Licon. 12000 microfarads, 63V. On the other
side they say LSM, 85C(M), VENT.

Terminals seem to be two pins that pass through pcb. (Don't know the spacing
yet). Overall package about 34mm diameter & 46mm high.

How crucial is it to replace like with like? 12,000 seems to be an odd
value. Most catalogues that I've looked at so far list 10,000 & 15,000
microfarad capacitors but not 12,000. Is there any harm in "over-specing"
slightly?

No..none at all.

They are generally -20%+50% anyway.

I HOPE that fixes it..but hum and hum reduction is a black art..I spent
about 6 months tracking down one cause after another on one design..


Tim

Tim Downie wrote:
The Natural Philosopher wrote:
Bob Mannix wrote:

All the responses so far have assumed an amplified hum signal. This
unit has a built in amplifier and it's possible the mains
transformer for the power supply is physically humming/vibrating as
it is loose or has become so and it's nothing to do with leads,
connections etc. This would sound like it was coming out of the
speaker.
That is entirely possible. Though quality kit will generally use a
toroid that should not be too bad in that respect.

It is a toroid. Is it safe to power it up with the speaker disconnected to
check that it's not coming from the transformer?

Tim


Almost certainly yes. Only older valve amps would over voltage on no load.

In article ,
Tim Downie wrote:
How crucial is it to replace like with like? 12,000 seems to be an odd
value. Most catalogues that I've looked at so far list 10,000 & 15,000
microfarad capacitors but not 12,000. Is there any harm in
"over-specing" slightly?

Higher capacity or working voltage won't matter - but it will likely be
bigger.

--
*If you must choose between two evils, pick the one you've never tried before

Dave Plowman London SW
To e-mail, change noise into sound.

Serge Auckland wrote:

I would not worry about replacing like with like, just get some caps that
will physically fit and are at least 12 mFds. 15mFd is fine. I would like to
know, however, why they failed after only 5-6 years. If I were doing this, I
would try and get some high-temperature capacitors which hopefully won't
fail so quickly.


The answer, as you suggest, is normally temperature. Really good quality
electrolytics are unlikely to be rated at more than 5000 hours at the
maximum temperature, some as little as 1000 hours. Increased life at
lower temperature seems based on the old rate-of-reaction exponential,
doubling about every 9-10 degrees drop. Not that it's an easy thing to
estimate.

Hunting down suitable capacitor replacements for my sub-woofer is turning
out a lot harder than I was expecting.

I've googled oodles of sites but can't find anything *near* the right spec.

It's a 12000 micro farad 63v electrolytic jobbie. A "radial" type (stubby
cyclinder, two pins at the bottom for soldering to PCB). Needs to be no
more than 35 mm diameter and preferably 45 mm tall (although there is room
for more height).

Other info, it has LSM, 85C(M) and VENT printed down the side (and it was
made by LICON).

I can't find anything with those values and even if I over-spec, I can't
find anything close enough.

Can anyone help?

Tim

Tim Downie wrote:
Hunting down suitable capacitor replacements for my sub-woofer is turning
out a lot harder than I was expecting.

I've googled oodles of sites but can't find anything *near* the right spec.

It's a 12000 micro farad 63v electrolytic jobbie. A "radial" type (stubby
cyclinder, two pins at the bottom for soldering to PCB). Needs to be no
more than 35 mm diameter and preferably 45 mm tall (although there is room
for more height).

Other info, it has LSM, 85C(M) and VENT printed down the side (and it was
made by LICON).

I can't find anything with those values and even if I over-spec, I can't
find anything close enough.

Can anyone help?

Farnell have a selection of 10000uF and 15000uF examples. (Start at
http://uk.farnell.com and try searching for capacitor. All the result
URLs I found include a sessionid so that'll time out and not be
generally useful.) The slightly under-spec part is much cheaper...

Another common recommendation is CPC.

Maplin seem to have thoughtfully discontinued their 10000uF stock.
They have almost completely morphed into a purveyor of consumer crap.
I struggle to work out how to buy some of the stuff they sell and/or
choose a sales droid who looks like they might be able to help.

--
"If it works, tear it apart and find out why!"

On Mar 7, 1:54 pm, "Tim Downie"
wrote:
Hunting down suitable capacitor replacements for my sub-woofer is turning
out a lot harder than I was expecting.

I've googled oodles of sites but can't find anything *near* the right spec.

It's a 12000 micro farad 63v electrolytic jobbie. A "radial" type (stubby
cyclinder, two pins at the bottom for soldering to PCB). Needs to be no
more than 35 mm diameter and preferably 45 mm tall (although there is room
for more height).

Other info, it has LSM, 85C(M) and VENT printed down the side (and it was
made by LICON).

I can't find anything with those values and even if I over-spec, I can't
find anything close enough.

Can anyone help?

Tim

Hi

RS Part Number 2508869138

12,000uF
63V
35mm Diameter, 50mm Length

Regards,

Steve

On Mar 7, 3:17 pm, "stevelup" wrote:

Hi

RS Part Number 2508869138

12,000uF
63V
35mm Diameter, 50mm Length

Regards,

Steve

CPC have a 10,000uF part in stock

http://cpc.farnell.com/jsp/endecaSea...sp?SKU=CA01667

Regards,

Steve

On Mar 7, 3:19 pm, "stevelup" wrote:
On Mar 7, 3:17 pm, "stevelup" wrote:

Hi

RS Part Number 2508869138

12,000uF
63V
35mm Diameter, 50mm Length

Regards,

Steve

CPC have a 10,000uF part in stock

http://cpc.farnell.com/jsp/endecaSea...sp?SKU=CA01667

Regards,

Steve


I must stop replying to myself... I spotted an interesting thing in
the datasheet - the lifespan of this part is 12000 hours - which isn't
an awful lot.

Assuming it's on for six hours a day, that's less than six years.

Regards,

Steve

On 7 Mar 2007 07:24:31 -0800, "stevelup" wrote:

On Mar 7, 3:19 pm, "stevelup" wrote:
On Mar 7, 3:17 pm, "stevelup" wrote:

Hi

RS Part Number 2508869138

12,000uF
63V
35mm Diameter, 50mm Length

Regards,

Steve

CPC have a 10,000uF part in stock

http://cpc.farnell.com/jsp/endecaSea...sp?SKU=CA01667

Regards,

Steve


I must stop replying to myself... I spotted an interesting thing in
the datasheet - the lifespan of this part is 12000 hours - which isn't
an awful lot.

Assuming it's on for six hours a day, that's less than six years.


That'll be specced at maximum operating temp. In any more normal
application you can expect vastly more than that.

d

--
Pearce Consulting
http://www.pearce.uk.com

"stevelup" wrote in message
ups.com...
On Mar 7, 3:19 pm, "stevelup" wrote:
On Mar 7, 3:17 pm, "stevelup" wrote:

Hi

RS Part Number 2508869138

12,000uF
63V
35mm Diameter, 50mm Length

Regards,

Steve

CPC have a 10,000uF part in stock

http://cpc.farnell.com/jsp/endecaSea...sp?SKU=CA01667

Regards,

Steve


I must stop replying to myself... I spotted an interesting thing in
the datasheet - the lifespan of this part is 12000 hours - which isn't
an awful lot.

Assuming it's on for six hours a day, that's less than six years.

Regards,

Steve


Interesting! I checked a few manufacturers and 12000 hours seems towards
the top of the specifications, some specifying a lot lower. This got me
thinking about broadcast equipment which is usually put into service and
left powered up until it is taken out of service perhaps 15-25 years later.
This is particularly so with transmission equipment which is normally
expected to have a 25 year life.

One year has 8760 hours, so stuff left on for 20 years will be operating for
175,000 hours. I have equipment at home that's been on for well in excess of
50,000 hours (standby operation still has the power supply on) so I wonder
what the 12,000 hours actually refers to.

S.

stevelup wrote:
On Mar 7, 3:19 pm, "stevelup" wrote:
On Mar 7, 3:17 pm, "stevelup" wrote:

Hi
RS Part Number 2508869138
12,000uF
63V
35mm Diameter, 50mm Length
Regards,
Steve
CPC have a 10,000uF part in stock

http://cpc.farnell.com/jsp/endecaSea...sp?SKU=CA01667

Regards,

Steve


I must stop replying to myself... I spotted an interesting thing in
the datasheet - the lifespan of this part is 12000 hours - which isn't
an awful lot.

Assuming it's on for six hours a day, that's less than six years.


As I pointed out elsewhere, that's at the maximum temperature, and
derating appears roughly exponential. At 30 degrees C less than its
rated temperature, which is not unreasonable, it might last five to
ten times that.

I don't think 12000 hours is bad for an electrolytic. The old rule
of thumb was seven years, though of course many go far beyond that.
A bit like hard drives.

Tim Downie wrote:

Can anyone help?

Farnell have a few 15000uF that come close to your spec:

e.g.

http://uk.farnell.com/jsp/endecaSear...sp?SKU=9348263

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wed, 07 Mar 2007 15:44:47 +0000, Joe wrote:

I don't think 12000 hours is bad for an electrolytic. The old rule
of thumb was seven years, though of course many go far beyond that.
A bit like hard drives.

I've got an AR88D with some electrolytics coming up for their 70th
rather than 7th birthday :-).

--
Peter Parry.
http://www.wpp.ltd.uk/

On 7 Mar, 15:44, Joe wrote:

I don't think 12000 hours is bad for an electrolytic. The old rule
of thumb was seven years, though of course many go far beyond that.
A bit like hard drives.

Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.


NT

In message .com,
writes
Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.

The failure of electrolytics over time is due to the drying out of the
electrolyte. The capacitor will generally read the correct value on a
capacitance meter but will develop a high ESR (Equivalent series
Resistance) which causes ripple on a supposedly smooth DC supply. (And
timing problems in old circuitry.)

When your old TV starts to hum and there is a dark ripple across the
screen or the picture tears away at the corner.... That's a dying
electrolytic.


I missed the start of this thread. Is the subwoofer humming even when
the audio source is disconnected?

--
Clive Mitchell
http://www.bigclive.com

wrote:
On 7 Mar, 15:44, Joe wrote:

I don't think 12000 hours is bad for an electrolytic. The old rule
of thumb was seven years, though of course many go far beyond that.
A bit like hard drives.

Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.


Well I had to fix an old valve radio that was late 50's vintage..that
had packed in its electrolytics after about 40 years.


Lost of valve stuff has that as the single and only real fault.


NT

Clive Mitchell wrote:
In message .com,
writes
Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.

The failure of electrolytics over time is due to the drying out of the
electrolyte. The capacitor will generally read the correct value on a
capacitance meter but will develop a high ESR (Equivalent series
Resistance) which causes ripple on a supposedly smooth DC supply. (And
timing problems in old circuitry.)

When your old TV starts to hum and there is a dark ripple across the
screen or the picture tears away at the corner.... That's a dying
electrolytic.


I missed the start of this thread. Is the subwoofer humming even when
the audio source is disconnected?


well it hums only when the *mains* IS connected..and on..

In message , The Natural
Philosopher writes
well it hums only when the *mains* IS connected..and on..

If it's just the mains and no signal then it sounds like either the PSU
capacitor as suggested or maybe just sloppy circuitry picking up hum.
Maybe even bad placement of cables inside if it's an active unit.

--
Clive Mitchell
http://www.bigclive.com

On Thu, 08 Mar 2007 00:54:51 +0000, The Natural Philosopher
wrote:

wrote:
On 7 Mar, 15:44, Joe wrote:

I don't think 12000 hours is bad for an electrolytic. The old rule
of thumb was seven years, though of course many go far beyond that.
A bit like hard drives.

Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.


Well I had to fix an old valve radio that was late 50's vintage..that
had packed in its electrolytics after about 40 years.


Lost of valve stuff has that as the single and only real fault.

Exactly. When I was a teenager (can't remember when that was, but a
while ago), I'd fix old valve radios for relatives, friends,
neighbours and assorted hangers on.

The most common fault by far was a failed smoothing capacitor leading
to a hum. I had a box of assorted diameter ones that would fit the
clip on the chassis. It didn't particularly matter if they were
larger capacitance than the original.

The second was that they had left the radio tuned to one station for
donkeys years (normally the Light Programme or Home Service) and now
wanted to tune to something else. Of course, the tuning capacitor
would be crudded up and would cause crackles or have intermittent
contact requiring "mechanical treatment" of the set.
A quick go with the vacuum cleaner and a squirt of contact cleaner
usually fixed these.

The third, but fortunately extremely rare one was a failed selenium
rectifier. When these are on their way out, they emit the most evil
of smells known to man and having a strong emetic effect.

Any of these repairs would bring forth a nice afternoon tea plus an
amount of folding that was way in excess of the time and materials
cost of the repair.

Regarding electrolytics in these old pieces of equipment, the failure
mode was pretty obvious - I took several apart for curiosity. Inside
they would be packed with some kind of gunk soaking the dielectric. On
working ones this would be quite gooey. On failed ones it had
hardened and become cracked. The hum wouldn't suddenly appear but
would get worse over the years until it was noticably bad in
comparison with something else like the TV.


--

..andy

On 7 Mar, 23:39, Clive Mitchell wrote:
In message .com,
writes

Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.

The failure of electrolytics over time is due to the drying out of the
electrolyte. The capacitor will generally read the correct value on a
capacitance meter but will develop a high ESR (Equivalent series
Resistance) which causes ripple on a supposedly smooth DC supply. (And
timing problems in old circuitry.)

It seems no-one can backup this 7 yr rule so far. Its far removed from
my experience with lytics, and lord knows I've worked with enough of
them. IME around 4 out of 5 1930s ones have still worked, so thats a
mttf of ballpark 70 x 4 = 280 yrs.

I'm surprised by Andy's experience, I've also fixed lots of valve kit,
and lytic failures have happpened but been fairly rare.

If there had been any sort of 7 yr rule, a lot of the new kit I've
worked on would never have got out the door, as 7 yr life would have
been unacceptably short.


NT

On 8 Mar 2007 02:00:42 -0800, wrote:

On 7 Mar, 23:39, Clive Mitchell wrote:
In message .com,
writes

Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.

I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.

The failure of electrolytics over time is due to the drying out of the
electrolyte. The capacitor will generally read the correct value on a
capacitance meter but will develop a high ESR (Equivalent series
Resistance) which causes ripple on a supposedly smooth DC supply. (And
timing problems in old circuitry.)

It seems no-one can backup this 7 yr rule so far. Its far removed from
my experience with lytics, and lord knows I've worked with enough of
them. IME around 4 out of 5 1930s ones have still worked, so thats a
mttf of ballpark 70 x 4 = 280 yrs.

I'm surprised by Andy's experience, I've also fixed lots of valve kit,
and lytic failures have happpened but been fairly rare.

If there had been any sort of 7 yr rule, a lot of the new kit I've
worked on would never have got out the door, as 7 yr life would have
been unacceptably short.


NT

Bear in mind that the lifetime of electrolytics will follow some kind
of normal distribution curve, and the quoted seven years will
represent the very start of the lower end of the tail - probably 0.1%
of the entire distribution, maybe even less. So the average life is
probably more like twenty or thirty years, with the upper tail
extending possibly to a hundred or so.

d

--
Pearce Consulting
http://www.pearce.uk.com

Don Pearce wrote:
On 8 Mar 2007 02:00:42 -0800, wrote:

On 7 Mar, 23:39, Clive Mitchell wrote:
In message .com,
writes
Where do you get the 7 year rule from, and what exactly is it? I've
never come across it, and if it existed I really ought to know.
I've still got 1930s lytics in service, and IME lytics are a long way
down the list of most likely failures in old equipment. The ida that
lytics have short lives seems to be an offshoot of the spate of bad
caps on mobos in the 90s.
The failure of electrolytics over time is due to the drying out of the
electrolyte. The capacitor will generally read the correct value on a
capacitance meter but will develop a high ESR (Equivalent series
Resistance) which causes ripple on a supposedly smooth DC supply. (And
timing problems in old circuitry.)
It seems no-one can backup this 7 yr rule so far. Its far removed from
my experience with lytics, and lord knows I've worked with enough of
them. IME around 4 out of 5 1930s ones have still worked, so thats a
mttf of ballpark 70 x 4 = 280 yrs.

I'm surprised by Andy's experience, I've also fixed lots of valve kit,
and lytic failures have happpened but been fairly rare.

If there had been any sort of 7 yr rule, a lot of the new kit I've
worked on would never have got out the door, as 7 yr life would have
been unacceptably short.


NT

Bear in mind that the lifetime of electrolytics will follow some kind
of normal distribution curve, and the quoted seven years will
represent the very start of the lower end of the tail - probably 0.1%
of the entire distribution, maybe even less. So the average life is
probably more like twenty or thirty years, with the upper tail
extending possibly to a hundred or so.

d

Certainly when called upon to fix the valve radio, I did a lot of web
research, and it was, with selenium rectifiers, the largest single problem.

Ageing coils needing tweaking and ageing valves were most of the others.

resistors rarely go, and in modern kit semiconductors are nearly as good.

Dry joints in PCB's are the final big failure mode.