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Marky P September 28th 08 09:42 PM

Testing capacitors
 
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?


Marky P.

David Looser September 28th 08 10:03 PM

Testing capacitors
 
"Marky P" wrote in message
...
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?

If you want to test capacitors reliably you need an ESR (Effective series
resistance) meter, not a capacitance one.

Otherwise testing by substitution is your best bet.

David.



Dave Plowman (News) September 28th 08 11:38 PM

Testing capacitors
 
In article ,
Marky P wrote:
Is it possible to test capacitors reliably without a capacitance
meter?


A 'capacitance meter' doesn't really test caps. For electrolytics you need
an ESR meter. They're fairly expensive so probably the best means of
testing is substitution.

--
*If at first you do succeed, try not to look too astonished.

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

Phil Allison September 29th 08 12:29 AM

Testing capacitors
 

"Marky P"


Is it possible to test capacitors reliably without a capacitance
meter?


** No * ONE * test ( or cap tester) will establish that a capacitor is
perfectly OK, however, if a cap fails even one important test - is IS
faulty.

Different types of caps have different electrical characteristics, ie
electros are very different from plastic film or ceramic types - so the
tests you do must suit the type of cap.




...... Phil





Phil Allison September 29th 08 04:47 AM

Testing capacitors
 

"David Looser"
"Marky P"

Is it possible to test capacitors reliably without a capacitance
meter?

If you want to test capacitors reliably you need an ESR (Effective series
resistance) meter, not a capacitance one.



** That only applies to electrolytic caps - plus the name is "equivalent
series resistance".

Plus an ESR meter will NOT find electro caps that have excessive leakage,
de-polarised or even become short circuit.

Capacitance meters are basically only handy when you have caps with no
markings, ambiguous markings or an unknown colour code.


...... Phil






David Looser September 29th 08 08:13 AM

Testing capacitors
 
"Phil Allison" wrote in message
...

"David Looser"
"Marky P"

Is it possible to test capacitors reliably without a capacitance
meter?

If you want to test capacitors reliably you need an ESR (Effective series
resistance) meter, not a capacitance one.



** That only applies to electrolytic caps -


True, but with modern equipment the vast majority of faulty capacitors are
electrolytics. Of course if he was talking about pre-1960 equipment then
leaky paper capacitors are almost a given.

plus the name is "equivalent series resistance".


Both terms are used. In this context they are equivalent because they
effectively mean the same thing.

Plus an ESR meter will NOT find electro caps that have excessive
leakage, de-polarised or even become short circuit.


Agreed, but these faults are readily apparent with normal testing methods.

Capacitance meters are basically only handy when you have caps with no
markings, ambiguous markings or an unknown colour code.

Agreed.

David.



Don Pearce September 29th 08 08:28 AM

Testing capacitors
 
Marky P wrote:
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?


Marky P.


By test, do you mean "is it working ok?" or do you want to measure the
value accurately?

For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok. For a more complete picture you need a
proper capacitor that will do several things - measure the actual
capacitance, put an appropriate voltage across it, measure the ESR and
the leakage resistance.

d

Phil Allison September 29th 08 01:48 PM

Testing capacitors
 

"David Looser the Brain Dead Lying **** "


Is it possible to test capacitors reliably without a capacitance
meter?

If you want to test capacitors reliably you need an ESR (Effective
series resistance) meter, not a capacitance one.



** That only applies to electrolytic caps -


True, but with modern equipment the vast majority of faulty capacitors...



** So ****ing what ?

The OP never alluded to what sort of caps he wanted to test.

So your assumption is 100% FALSE !!!!!!!!



plus the name is "equivalent series resistance".


Both terms are used.



** Complete ********.


Plus an ESR meter will NOT find electro caps that have excessive
leakage, de-polarised or even become short circuit.


Agreed,



** So your assertion above is a 100% total pile of CRAP.

Just like you - sunshine.




...... Phil







Phil Allison September 29th 08 01:53 PM

Testing capacitors
 

"Don Pearce the Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.



** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.




....... Phil




Don Pearce September 29th 08 02:17 PM

Testing capacitors
 
Phil Allison wrote:
"Don Pearce the Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.



** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.




...... Phil




You don't have a multimeter with a needle? You are missing one of the
best alignment tools anyone could own - and a handy capacitor tester of
course. Go out and buy one now - it isn't a replacement for a DMM, but a
very useful complement.

d

Phil Allison September 29th 08 02:38 PM

Testing capacitors
 

"Don Pearce Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.



** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.

IMBECILE




...... Phil





Dave Plowman (News) September 29th 08 03:07 PM

Testing capacitors
 
In article ,
Don Pearce wrote:
You don't have a multimeter with a needle? You are missing one of the
best alignment tools anyone could own - and a handy capacitor tester of
course. Go out and buy one now - it isn't a replacement for a DMM, but a
very useful complement.


Absolutely. But you can't expect bar room 'experts' like our Phil to know
such things...

--
*The only difference between a rut and a grave is the depth.

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

Roger Thorpe[_2_] September 30th 08 10:03 AM

Testing capacitors
 
Phil Allison wrote:
"Don Pearce Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.



** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.

IMBECILE




..... Phil




Try
http://www.maplin.co.uk/Module.aspx?ModuleNo=25414

You really must learn to control that temper

Roger

Ian[_3_] September 30th 08 09:11 PM

Testing capacitors
 

"Marky P" wrote in message
...
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?


Marky P.


Yes, put your tongue across the contacts a few seconds after switching off.



Patrick Turner October 1st 08 09:34 AM

Testing capacitors
 


David Looser wrote:

"Marky P" wrote in message
...
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?

If you want to test capacitors reliably you need an ESR (Effective series
resistance) meter, not a capacitance one.

Otherwise testing by substitution is your best bet.

David.



Its possible measure the value of capacitance using a low Rout signal
generator feeding a potentiometer in series with the capacitor with one
lead grounded. A volt meter is used to measure signal voltage across the
C. Set the signal gene at 10.0V sine wave at some chosen F. Alter the
value of the series resistance until you see 7.07Vrms appear across the
capacitor.
Disconnect the pot without altering its resistance, then measure its
resistance accurately.

C in uF then can be calculated = 159,000 / ( R in ohms x frequency ) so
say you had R = 5,000 ohms, and F = 1.0kHz, then C = .0318uF .

You could also have an air cored inductor of known inductance, and
parallel the C with the L, and feed it with a signal from a 10k
resistance from the sig gene. Using an osciloscope, tune the gene F for
the highest peak in resonance, known as Fo. Record Fo.

C in uF = 25.351 x 1,000,000 / F in Hz squared x L in milliHenrys.

Eg, if L = 100mH, F = 1kHz = 1,000 Hz, C = 0.251uF.

There are other ways using an old fashioned bridge.

ESR is measured in other ways, but it seems the OP wanted to know how to
work out the C value without a C meter.

Many cheap DVMs now sold measures C very well.

But they don't always measure L very well, espcially iron cored items
with variable L value at different F and V applied.

Patrick Turner.

Patrick Turner October 1st 08 09:40 AM

Testing capacitors
 


Phil Allison wrote:

"Marky P"

Is it possible to test capacitors reliably without a capacitance
meter?


** No * ONE * test ( or cap tester) will establish that a capacitor is
perfectly OK, however, if a cap fails even one important test - is IS
faulty.

Different types of caps have different electrical characteristics, ie
electros are very different from plastic film or ceramic types - so the
tests you do must suit the type of cap.


Indeed, and I forgot these valid points in my last post.

Testing for leakage current can be done by applying dc voltage via a
100k to the cap and measuring the voltage drop across the 100k R over
some long time. But the voltage across the cap must not exceed the value
marked on the cap for all caps,
and for electros, the cap voltage should not be less than 1/4 of the
working Vdc marked on the cap.

I think the OP mainly wanted the C value.

Patrick Turner.

..... Phil


David Looser October 1st 08 09:42 AM

Testing capacitors
 
"Patrick Turner" wrote in message
...



ESR is measured in other ways, but it seems the OP wanted to know how to
work out the C value without a C meter.

Does it? the OP talked about "testing" a capacitor, not "measuring" it; that
sounds to me more like someone who wanted to know whether a capacitor was
faulty.

Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.



Patrick Turner October 1st 08 09:50 AM

Testing capacitors
 


Phil Allison wrote:

"Don Pearce the Geriatric Fool "

For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.


** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?

Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.

...... Phil


Calm down Phil. You'll give grandad a heart attack.

The ohm test across a C does give some indication of the status of the
C.
If the cap is shorted, a DMM just shows a very low R number immediately.

If its not shorted, and doesn't have a stored charge (that well might
bend a meter needle in granpa's work shed), then the DMM will eventually
read OL for most plastic caps at least after some time as the cap
charges up with applied Vdc from the meter via the meter's series high
output resistance.

Most ohm meters produce a very low Vdc to test ohm values and a cap's
integrity needs to be tested at a Vdc across the cap for quite some time
and near the V rating of the cap, and when the temp is raised to near
operational if need be and with a CRO connected across the cap to detect
Vdc movements or intermittent noise/arcing in the cap.

Patrick Turner.

Patrick Turner October 1st 08 10:05 AM

Testing capacitors
 


Don Pearce wrote:

Phil Allison wrote:
"Don Pearce the Geriatric Fool "


For a quick and dirty test, just connect a multimeter on the ohms range.
The needle should flick across to short circuit, then drop back towards
high resistance. The time it takes to drop back is proportional to the
value of the capacitor. If the needle ultimately drops back to open
circuit, the cap is probably ok.



** ROTFLMFAO !!!!!!!!!!

Hey grand-dad !!

Got any ****ing idea how long it is since " multimeters " had needles ??

Bet your pathetic old AVO has a nice BENT one - eh ?


Why don't you **** the HELL off - grand dad -

& spare the planet you dumb as dog **** WRONG advice.




...... Phil




You don't have a multimeter with a needle? You are missing one of the
best alignment tools anyone could own - and a handy capacitor tester of
course. Go out and buy one now - it isn't a replacement for a DMM, but a
very useful complement.


I have several analog and digital meters in my shed. But 99% of what i
measure is done with a Fluke DMM.

I got the analog meters for almost free at ham fests and dumpster bins.
Some I have calibrated for voltage measurement using an opamp drive with
diode in the shunt FB path so the meter reads logarithmically. These are
then calibrated in up to 30dB each side of a centre idle point, making
readings of speaker responses quite easy and accurate enough over 33
chosen filter Fo of the audio band. The signals measured are those
recovered from a pink noise source fed to the speaker, and a mic signal
amplified and filtered by a bandpass filter with Q = 12 at all F.

Its an old fashioned thing I made before I got a PC. I have not got
around to buying a Spectral analyser program to display speaker response
immediately on a PC screen, and variably as you change the mic position,
or alter a cross over component.

But it tells me 90% of what I need to know about loudspeakers. And if
the C values in crossovers were correct, or labelled correctly at the
factory; sometimes you get old "100uF" caps but they measure say 52uF,
but look perfect, and have not obviously dried out, and sometimes much
more C is there than the amount on the can. But its never an accurate
way to measure the C in crossovers, so see my other posts.

Patrick Turner.





d


Phil Allison October 1st 08 02:02 PM

Testing capacitors
 

"Patrick Turner"


Indeed, and I forgot these valid points in my last post.


I think the OP mainly wanted the C value.



** Then it would indeed profit the good fellow - most greatly -

to learn how to ****ING READ !!!!!!!!!!!!




........ Phil







Eeyore October 2nd 08 06:18 AM

Testing capacitors
 


Don Pearce wrote:

You don't have a multimeter with a needle? You are missing one of the
best alignment tools anyone could own - and a handy capacitor tester of
course. Go out and buy one now - it isn't a replacement for a DMM, but a
very useful complement.


Handy for measuring noise too due to the mechanical time constant. Noise tends
to send DVMs nuts.

Graham


Patrick Turner October 2nd 08 09:28 AM

Testing capacitors
 


Phil Allison wrote:

"Patrick Turner"


Indeed, and I forgot these valid points in my last post.


I think the OP mainly wanted the C value.


** Then it would indeed profit the good fellow - most greatly -

to learn how to ****ING READ !!!!!!!!!!!!

....... Phil


"The good fellow" ??

I didn't think there was one left...

Patrick Turner

Marky P October 3rd 08 03:26 PM

Testing capacitors
 
On Wed, 1 Oct 2008 10:42:53 +0100, "David Looser"
wrote:

"Patrick Turner" wrote in message
...



ESR is measured in other ways, but it seems the OP wanted to know how to
work out the C value without a C meter.

Does it? the OP talked about "testing" a capacitor, not "measuring" it; that
sounds to me more like someone who wanted to know whether a capacitor was
faulty.

Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder

Marky P.

Marky P October 3rd 08 03:39 PM

Testing capacitors
 
On Tue, 30 Sep 2008 22:11:57 +0100, "Ian"
wrote:


"Marky P" wrote in message
.. .
Hi,

Is it possible to test capacitors reliably without a capacitance
meter?


Marky P.


Yes, put your tongue across the contacts a few seconds after switching off.

A bit more awkward when the caps are still on the board :-)


Marky P.

David Looser October 3rd 08 03:47 PM

Testing capacitors
 
"Marky P" wrote in message
...
On Wed, 1 Oct 2008 10:42:53 +0100, "David Looser"
wrote:


Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder


Faulty capacitors in power supplies usually make themselves apparent by such
problems as low voltage or excessive ripple on one or more of the output
lines, or rather more obviously by leaking electrolyte, bulging seals etc.
In view of the age of this unit your best bet is probably simply to replace
any suspect capacitors rather than bothering to try and test them.

David.



Dave Plowman (News) October 3rd 08 04:08 PM

Testing capacitors
 
In article ,
Marky P wrote:
Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder


Which one?

If an analogue PS a faulty cap would usually just cause hum, etc. If
switch mode you'll really need an ESR metre to check them.

--
*It ain't the size, it's... er... no, it IS ..the size.

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

Marky P October 3rd 08 07:43 PM

Testing capacitors
 
On Fri, 3 Oct 2008 16:47:49 +0100, "David Looser"
wrote:

"Marky P" wrote in message
.. .
On Wed, 1 Oct 2008 10:42:53 +0100, "David Looser"
wrote:


Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder


Faulty capacitors in power supplies usually make themselves apparent by such
problems as low voltage or excessive ripple on one or more of the output
lines, or rather more obviously by leaking electrolyte, bulging seals etc.
In view of the age of this unit your best bet is probably simply to replace
any suspect capacitors rather than bothering to try and test them.

David.

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable. The caps were
replaced and the problem was rectified. Well, within a couple of
months the fault is back, and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Marky P.

Marky P October 3rd 08 07:44 PM

Testing capacitors
 
On Fri, 03 Oct 2008 17:08:43 +0100, "Dave Plowman (News)"
wrote:

In article ,
Marky P wrote:
Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder


Which one?

If an analogue PS a faulty cap would usually just cause hum, etc. If
switch mode you'll really need an ESR metre to check them.


As mentioned in the above post, it's a Saturn Soundcraft 24 track.

Marky P.

David Looser October 3rd 08 08:28 PM

Testing capacitors
 
"Marky P" wrote in message
...

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.


Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

The caps were
replaced


All of them?

and the problem was rectified. Well, within a couple of
months the fault is back,


So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the result
of a broken PCB track, dry joint or poor connection somewhere that makes
contact when it wants too, and the "cure" last time was due to the physical
handling of the PSU causing this to make contact again, for a while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

David.



Patrick Turner October 5th 08 08:38 AM

Testing capacitors
 


Marky P wrote:

On Wed, 1 Oct 2008 10:42:53 +0100, "David Looser"
wrote:

"Patrick Turner" wrote in message
...



ESR is measured in other ways, but it seems the OP wanted to know how to
work out the C value without a C meter.

Does it? the OP talked about "testing" a capacitor, not "measuring" it; that
sounds to me more like someone who wanted to know whether a capacitor was
faulty.

Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder

Marky P.


Try just replacing it with another of the right type. If the problem of
noise or silence vanishes, maybe its the cap. Hire a tech to find out
for you? every tech knows what to do about testing a cap for a
fault/leakage and its been discussed many times here and else where.

Reading the circuit should inform you of the Vdc across the cap and hum
voltage, so if there is a lot of hum and Vdc is low, and there are hot
parts, then maybe the circuit powered by the Vdc is drawing too much
Idc. Take the wholeistic approach, or else put up with wrong
diagnosies.

Patrick Turner.

Graham.[_2_] October 5th 08 10:13 PM

Testing capacitors
 


Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.


Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

The caps were
replaced


All of them?

and the problem was rectified. Well, within a couple of
months the fault is back,


So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the
result of a broken PCB track, dry joint or poor connection somewhere that
makes contact when it wants too, and the "cure" last time was due to the
physical handling of the PSU causing this to make contact again, for a
while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.


Excatly what I thought.
Mind you they do a very good line of condensers on the planet Metaluna.
http://en.wikipedia.org/wiki/This_Island_Earth

--
Graham.

%Profound_observation%



Serge Auckland[_2_] October 6th 08 08:19 AM

Testing capacitors
 

"David Looser" wrote in message
...
"Marky P" wrote in message
...

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.


Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

The caps were
replaced


All of them?

and the problem was rectified. Well, within a couple of
months the fault is back,


So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the
result of a broken PCB track, dry joint or poor connection somewhere that
makes contact when it wants too, and the "cure" last time was due to the
physical handling of the PSU causing this to make contact again, for a
while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

David.


What's wrong with Bury St Edmunds? My designs generally work.......
S.
--
http://audiopages.googlepages.com


Marky P October 6th 08 06:48 PM

Testing capacitors
 
On Fri, 3 Oct 2008 21:28:09 +0100, "David Looser"
wrote:

"Marky P" wrote in message
.. .

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.


Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?


Unfortunately I haven't looked at it myself, so I don't know.

The caps were
replaced


All of them?


Again, I'm not sure. Wouldn't've thought so.

and the problem was rectified. Well, within a couple of
months the fault is back,


So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the result
of a broken PCB track, dry joint or poor connection somewhere that makes
contact when it wants too, and the "cure" last time was due to the physical
handling of the PSU causing this to make contact again, for a while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

David.


Marky P.

Arny Krueger October 13th 08 10:01 PM

Testing capacitors
 
"Marky P" wrote in
message
Hi,

Is it possible to test capacitors reliably without a
capacitance meter?


Yes, if you have some fairly precise reference parts, you can set up a
capacitance bridge on the bench that allows you to measure capacitance and
series R by indirect means.

http://www.allaboutcircuits.com/vol_2/chpt_12/5.html



Glenn Richards October 20th 08 07:33 AM

Testing capacitors
 
Phil Allison wrote:

True, but with modern equipment the vast majority of faulty capacitors...

** So ****ing what ?
The OP never alluded to what sort of caps he wanted to test.
So your assumption is 100% FALSE !!!!!!!!


You know, when I see an outburst like this I always imagine the poster
sat at the computer wearing his underwear and a straight jacket, typing
by picking up a pencil in his teeth and dribbling everywhere.

Either that or wearing a dress like the character "Anne" in the popular
British comedy "Little Britain".

--
Squirrel Solutions Ltd Tel: (01453) 845735
http://www.squirrelsolutions.co.uk/ Fax: (01453) 843773

Registered in England: 05877408

Nick Gorham October 20th 08 09:13 AM

Testing capacitors
 
Glenn Richards wrote:
Phil Allison wrote:

True, but with modern equipment the vast majority of faulty
capacitors...


** So ****ing what ?
The OP never alluded to what sort of caps he wanted to test.
So your assumption is 100% FALSE !!!!!!!!



You know, when I see an outburst like this I always imagine the poster
sat at the computer wearing his underwear and a straight jacket, typing
by picking up a pencil in his teeth and dribbling everywhere.

Either that or wearing a dress like the character "Anne" in the popular
British comedy "Little Britain".



http://xkcd.com/386/

--
Nick

David Looser October 21st 08 12:20 PM

Testing capacitors
 
"Glenn Richards" wrote in message
...
Phil Allison wrote:

True, but with modern equipment the vast majority of faulty
capacitors...

** So ****ing what ?
The OP never alluded to what sort of caps he wanted to test.
So your assumption is 100% FALSE !!!!!!!!


You know, when I see an outburst like this I always imagine the poster sat
at the computer wearing his underwear and a straight jacket, typing by
picking up a pencil in his teeth and dribbling everywhere.

Either that or wearing a dress like the character "Anne" in the popular
British comedy "Little Britain".


And, as it turned out, my assumption was 100% correct!

David.




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