Audio amplifier repair - bad capacitors

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Hello,


When repairing audio amplifiers, would an ESR meter or a capacitance
meter be more useful in identifying bad capacitors in circuit?


Would either of these be any good:

'High Precision L/C Inductance Inductor Capacitance Multimeter Meter
LC200A Tool | eBay' (http://tinyurl.com/prdtqh7 )


'Capacitor/Capacitance ESR IN-Circuit Inductance Resistance Meter LC
Meter dc 9v | eBay' (Error)



Thanks.




--
M.Joshi


Re: Audio amplifier repair - bad capacitors
On 07/14/2013 8:35 AM, M.Joshi wrote:
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I've been selling the Bob Parker ESR meters (now BLUE) kit since 1999  
and they has been a great boon to technicians for fixing monitors,  
switching power supplies, and other devices with electrolytic  
capacitors. Great for caps larger than around 2ufd.

https://www.flippers.com/BlueEsr.html

Unfortunately smaller value caps (<2ufd) are harder to check in circuit  
and I can't speak to the ones on eBay. They may or may not live up to  
the ad.

I do know that Bob Parker's design works for our shop - that's why I've  
been happily selling them!

http://www.flippers.com/catalog/index.php/test-equipment-kits-c-3

John :-#)#

--  
    (Please post followups or tech enquiries to the newsgroup)
  John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
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Re: Audio amplifier repair - bad capacitors

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+1.

The Blue ESR meter saves a lot of time. Often the biggest delay is waiting  
on the spare parts.

tm  


Re: Audio amplifier repair - bad capacitors

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I dont think esr can prevent audio amplifiers from working
it prevents power supplies (especially switching) yes
there are lot of switching power supplies that may fail due to bad esr  
capacitor
but in an audio amplifier there is quite never a switching power supply

but an esr meter is very useful to the technician
but if you do only audio repair, you won't use it very often.

see below my web site for free esr schematics
--  
----------
Kripton

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Re: Audio amplifier repair - bad capacitors

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Don't work on many amps, do you?

Class D are all switching units. The power supply as well as the amp.





Re: Audio amplifier repair - bad capacitors
On Sun, 14 Jul 2013, tm wrote:

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I think the point is that generally audio amplifiers these days don't have  
that many electrolytic capacitors.  The circuitry is generally direct  
coupled, even at the output.  That's a big difference from early  
transistor amplifiers that suddenly used a slew of electrolytics.

And most amplifiers still use linear power supplies, so not only are the  
filter capacitors operating at a relatively low frequency, but they are  
few in number.  If you've got hum from the amplifier, chances are the  
filter capacitor is bad.  IN a switching supply, the supply may never  
start working if an electrolytic is bad.

Like I said earlier, one reason for ESR meters is the rise in the number  
of electrolytics.  If you can't easily tell which is causing the problem,  
it makes sense to have a meter that will check the electrolytics in  
circuit.  Especially if the circuit is still relatively "foreign" like a  
switching supply or other digital circuitry.  An audio amplifier is  
generally still a familiar thing, check where the audio disappears, check  
for voltages, etc.  There are a lot ore telltales than in a switching  
supply where mutliple things interact and still many people haven't had  
much experience with them.

In antique radio circles, it's all so much easier. 2 or 3 electrolytics,  
might as well just replace them, if they aren't bad now, they will go bad.
ANd yes, if it's old enough, just replace the other capacitors, since old  
enough means odd types of capacitors that can go bad.  The electrolytics  
are easy, not many of them.  The others people know from experience, so  
if you've got the radio open, might as well do them all.

Even odler transistor radios tend to get th shotgun treatment.  There are  
more electrolytics than in tubes, but still not that many and likely froma  
period when they would be failing by now. But again since the number are  
few, it;'s just as easy to replace them as to spend time trying to figure  
out what's wrong.

In modern equipment, not generally audio amplifiers, the circuit isn't  
obvious (and often no schematic), and so many electrolytics that it starts  
being cheaper to find the bad ones than just shotgun them all.

It really depends.  For someone just doing amplifiers, an ESR meter might  
not be that useful, they have other means of evaluating things.  If they  
did other things, then an ESR meter becomes valuable, and then they can  
use it on amplifiers, too.

   Michael


Re: Audio amplifier repair - bad capacitors
wrote:

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I beg to differ slightly.  Here's a lousy photo of the power amp and
power supply section from a Behringer PMH518M mono amplifier that had
a problem with bad capacitors:
<http://802.11junk.com/jeffl/pics/repair/slides/Behringer-PMH518M-PS.html
The two big caps (C6, C7), that are missing in the photo, were the
primary culprits[1].  Their high ESR caused major voltage excursions
to the regulator transistors, sufficient to blow up the devices and
fry the traces.  Other than some corrosive goo leaking from the rubber
seal on the bottom of the caps, there was no visible evidence that the
caps were not doing their job.  I didn't need an ESR meter to fix such
an obvious problem, but with less damage, it might have been helpful
to verify that the caps were still usable.  

I don't do much audio or video repair, but I am beginning to see Class
E switched amplifiers, mostly in computah speakers, which more
closesly resemble a switching power supply than a traditional linear
power amplifier.  I would expect capacitor ESR problems in those.


[1]  Hint:  The caps are 4700uf 50VDC running on a 40 VDC input bus to
the regulators.  Running caps at 80% of the maximum voltage, next to a
heat sink full of very warm devices, is not a great design, even at
120Hz.  I replaced them with 3300uf 63VDC caps.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Audio amplifier repair - bad capacitors
On Sunday, July 14, 2013 1:12:23 PM UTC-4, Kripton wrote:

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There are still a significant number of older audio amplifiers that use ele
ctrolytics in the coupling mode, so I guess an ESR meter is handy.

I have a Parker ESR meter and an older Sencore Z meter.  Both have on occas
ion reported normal ESR in an in circuit test that was false ie: removed ca
p showed bad ESR out of circuit, and the circuit-sans cap, still showed goo
d ESR with no cap installed). BTW, beware the resident troll that will pop  
up shortly and spew his vile garbage.  Regulars are already ducking...  

What I do now is mostly use my scope with the equipment up and running for  
both bypass and coupling caps.  Anything that doesn't look right gets pulle
d and checked on the Sencore for ESR, full voltage leakage, then recheck fo
r ESR.

Re: Audio amplifier repair - bad capacitors

<Kripton>
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** Nonsense.

Electro caps get old and wear out no matter what gear they are in -  heat is  
the main cause.

Audio amps get hot, tube ones very much so.

High ESR caps in an amplifier will cause hum, high and low frequency  
instability, loss of gain and even loss of signal entirely.

A good ESR meter allows you to find then before symptoms appear too.


...  Phil




Re: Audio amplifier repair - bad capacitors

"Arfa Daily"
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** A recent example of using my Bob Parker ESR meter was with a nicely made  
clone of a Fender "Princeton Reverb" combo amp. The amp was just a few years  
old and had all new components in it -  PLUS  a chassis made from Stainless  
Steel !!

However, it was riddled with faults like low frequency oscillation (  
motor-boating), loud hum and high frequency instability when the reverb was  
turned up.

The ESR meter read off scale ( ie over 100ohms) on three sections of the  
main filter electro and 20 ohms on the fourth  - it was one of these:

http://www.tubesandmore.com/products/C-EC20X4-475

New electros fixed all the faults.

When I opened the can of the old one, the aluminium strips linking the  
terminals to the insides were mostly eaten away with horrible corrosion.

My conclusion is that the electro was far from new -  more likely 50 year  
old stock that someone has found and re-labelled.

BTW:

Old electros can often still work fine, but not if left in storage for  
periods like 50 years.



....  Phil






Re: Audio amplifier repair - bad capacitors
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I would definitely want one with ESR-measuring capabilities.  From
what I've read (and in my own experience), electrolytic caps which
start to fail will usually show a significant increase in ESR well
before their capacitance changes significantly.

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That one looks similar to the AADE meter (http://aade.com/lcmeter.htm )
and might be one of the "knock-offs" that this page refers to.

I do like the AADE meter - it seems to work very well for what it's
intended to do.  It does capacitance measurements over a wide range
(pF up to 1.5 uF).

However, it is not intended or advertised as being useful for
in-circuit measurements, it doesn't have ESR-measuring capability, and
it isn't designed to measure the capacitance of all but the smallest
electrolytic caps.

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The one I see with this description looks more like what you'd
want... its capacitance measurement range covers typical electrolytics
(but not smaller film/ceramic caps), and it does multi-frequency
measurements which will give you both the capacitance and the ESR.

The two types of meters you've described here are really complementary
sorts of instruments... they both measure capacitors, but their ranges
of measurements barely overlap.  They're both useful but do different
sorts of things, and you wouldn'd do wrong by having one of each type.

The third type of measurement you might want to do for looking at
failed caps in an audio amp, would be a leakage test.  Inter-stage
coupling caps can become leaky, especially if there's no bias voltage
across them most of the time (or if they're reverse biased) and this
isn't something which will show up in a capacitance or ESR test.
Testing for leaky 'lytics is probably best done out-of-circuit,
though.

I built my own ESR meter a few years ago, based on the Ludens design
(http://ludens.cl/Electron/esr/esr.html ) and it's been quite useful.
Easily made using "junk box" parts, capable of doing in-circuit ESR
measurements safely, and un-critical in its construction, it's a great
weekend project.

Re: Audio amplifier repair - bad capacitors
On Sun, 14 Jul 2013 17:35:11 +0200, M.Joshi

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An ESR meter is a VERY useful tool for finding bad caps.

Most of these were found with an ESR meter over about a 3 month
period:
<http://802.11junk.com/jeffl/pics/repair/slides/bad-caps.html
While some of these caps show obvious bulges, many of them have no
visible signs of failure.

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No.  That's an L/C meter, not an ESR meter.  You can have a bad
capacitor, with a very high ESR and still show normal capacitance.  

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No experience with that one.  I'm suspicious because it doesn't say
anything about zeroing the probe cable resistance, which is necessary
for in-circuit measurements.

Search for one of the Bob Parker ESR meter designs.  I have one of the
original Dick Smith variety.  Works nicely.
<http://members.ozemail.com.au/~bobpar/esrmeter.htm
I suggest you read a little about how an ESR meter is used before
buying.


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Audio amplifier repair - bad capacitors

"M.Joshi"

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** An ESR meter is the only useful type.

The best one for all servicing work is the "Bob Parker" ESR and Low Ohms  
meter:

Just Google that name for heaps of hits.




...  Phil




Re: Audio amplifier repair - bad capacitors

"M.Joshi"

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** An ESR meter is the only useful type.

The best one for all servicing work is the "Bob Parker" ESR and Low Ohms  
meter:

Just Google that name for heaps of hits.




...  Phil




Re: Audio amplifier repair - bad capacitors

"M.Joshi"

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** An ESR meter is the only useful type.

The best one for all servicing work is the "Bob Parker" ESR and Low Ohms
meter:

Just Google that name for heaps of hits.




...  Phil





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