How to find failing capasitor
Shagalot
All,
Just want to know how can we determine whihc capasitor that fail if all the
capasitor are connected together in parralel. What happens if one of the
capasitor is shorted, how can we tell which?????
-------------------------- +Vcc
| | | | | | | |
c c c c c c c c
| | | | | | | |
------------------------- Gnd
Kew
Spehro Pefhany
> Just want to know how can we determine whihc capasitor that fail if all the
> capasitor are connected together in parralel. What happens if one of the
> capasitor is shorted, how can we tell which?????
Well, "shagalot", there are a number of (non-invasive) ways, all of which
depend on non-ideal behaviour of the connections. You could also just cut
wires and/or remove parts till you find it. Maybe you should post some
more details of your homew^H^H^H^H^H problem?
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany "The Journey is the reward"
sp...@interlog.com
Fax:(905) 332-4270 (small micro system devt hw/sw + mfg)
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
J. G. Simpson
If you have access to the leads (as with banks of power factor
correctors) then excite the bank (reduced voltage, or current
limiter resistor, to bank). Use a current probe, AC or Hall
effect DC, such as a Tektronix scope and current probe on each
lead in turn. The one drawing most current is the one to pull
and test.
If they are small capacitors on a PCB you have problems. If the
tracks to each cap are the same X-section then you might be able
to make a two prong current probe, coupled to a sensitive
micro-voltmeter, and use the PCB tracks as current sensing
resistors. But it isn't easy and depends a lot on the actual
circuit layout, whether all capacitors have the same value,
and the like.
Shagalot (shaga...@hotmail.com) wrote:
: All,
:
: Just want to know how can we determine whihc capasitor that fail if all the
: capasitor are connected together in parralel. What happens if one of the
: capasitor is shorted, how can we tell which?????
:
: -------------------------- +Vcc
: | | | | | | | |
: c c c c c c c c
: | | | | | | | |
: ------------------------- Gnd
:
: Kew
--
-------------
-------------
Sam Goldwasser
In article <01bd1d11$0f889220$e641bcca@default> "Shagalot" <shaga...@hotmail.com> writes:
> Just want to know how can we determine whihc capasitor that fail if all the
> capasitor are connected together in parralel. What happens if one of the
> capasitor is shorted, how can we tell which?????
> -------------------------- +Vcc
> | | | | | | | |
> c c c c c c c c
> | | | | | | | |
> ------------------------- Gnd
Where there is no physical evidence, the easiest is probably to disconnect
them in binary search fashion (half, quarter, etc.) and test each section.
Not elegant but simple!
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Lasers: http://www.geocities.com/CapeCanaveral/Lab/3931/lasersam.htm
Usually latest (ASCII): http://www.pacwest.net/byron13/sammenu.htm
Gary Woods
s...@stdavids.picker.com (Sam Goldwasser) wrote:
>
>Where there is no physical evidence, the easiest is probably to disconnect
>them in binary search fashion (half, quarter, etc.) and test each section.
>Not elegant but simple!
Depending on how thoroughly shorted, use a "shortfinder." An audible
ohmmeter that can resolve small variations in resistance. A good one
can tell which end of a short pc board trace the short is on.
Gary Woods, acting interim web guy, and technician at LARGE
Sam Goldwasser
> s...@stdavids.picker.com (Sam Goldwasser) wrote:
> >Where there is no physical evidence, the easiest is probably to =
> >disconnect them in binary search fashion (half, quarter, etc.) and
> >test each section. Not elegant but simple!
> Depending on how thoroughly shorted, use a "shortfinder." An audible
> ohmmeter that can resolve small variations in resistance. A good one
> can tell which end of a short pc board trace the short is on.
Of course, the classic case of this situation is where you have a PCB with
a zillion bypass caps and one is shorted!
Then, you really do need the current probe or micro-ohm ohmmeter especially
where there are ground and power planes.
John Woodgate
In article <01bd1d11$0f889220$e641bcca@default>, Shagalot
<shaga...@hotmail.com> writes
>All,
>Just want to know how can we determine whihc capasitor that fail if all the
>capasitor are connected together in parralel. What happens if one of the
>capasitor is shorted, how can we tell which?????
>
>-------------------------- +Vcc
> | | | | | | | |
> c c c c c c c c
> | | | | | | | |
>------------------------- Gnd
>
Do a DejaNews search for the recent thread on measuring the resistance
of PC board traces. A similar device will detect the current flow in the
trace. When you move it beyond the shorted cap., no more current (or at
least, a lot less).
--
Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124.
OOO - Own Opinions Only. You can fool all of the people some of the time, but
you can't please some of the people any of the time.
Nelson Navarro
Shagalot wrote:
>
> All,
>
> Just want to know how can we determine whihc capasitor that fail if all the
> capasitor are connected together in parralel. What happens if one of the
> capasitor is shorted, how can we tell which?????
>
> -------------------------- +Vcc
> | | | | | | | |
> c c c c c c c c
> | | | | | | | |
> ------------------------- Gnd
>
> Kew
We once had a power supply filter circuit with about a dozen or so small
ceramic capacitors in parallel and in close proximity. We found that if
we sprayed the capacitors with circuit cooler while energized, the
uneven distribution of the resulting frost would usually reveal the
defective capacitor.
Regards,
Nelson Navarro
Petercoe
Gee! It would take all of 5 minutes to unsolder one leg of each capacitor.
Pete...@aol.com
35 year tv repair
Tsum3Drac
How low resistance is the short? Doesn't one capacitor get hotter than the
rest?
You can measure the voltage across each cap (right at the leads) with a
precision DVM. The ability to track it down to a single capacitor depends
somewhat on the exact trace routing, but look for the cap with the lowest
voltage across it.
Sam Goldwasser
> Gee! It would take all of 5 minutes to unsolder one leg of each capacitor.
Hehe... Unless this was a power factor correction farm on the power grid :-).
Frank Bemelman
"Shagalot" <shaga...@hotmail.com> wrote:
>All,
>Just want to know how can we determine whihc capasitor that fail if all the
>capasitor are connected together in parralel. What happens if one of the
>capasitor is shorted, how can we tell which?????
>-------------------------- +Vcc
> | | | | | | | |
> c c c c c c c c
> | | | | | | | |
>------------------------- Gnd
>Kew
What about hooking it up to a real strong powersupply and adjust the
currentlimit at 4-5 amps (to prevent tracks blown off). Now, the smoke
will tell you where to look. The color of the smoke (grey or blue) is
not important ;-)
Another useful trick is just taking a close look. A slight
discoloration can indicate the bad cap. Of cource the shortage can
also be located in one of the chips on your board. Look for small
cracks in the package, small bubbles on the package. Sometimes you can
locate a defective component using your nose ! just sniff across the
board for bad smells. Even a perfectly looking component can give a
bad smell if it has been running out of specs for a while.
Best regards, Frank.
(remove 'x' when replying by email)
Tech Guy
You failed to mention whether the capacitors were all of the same value and if they were polarized or if the problem was a short or an open!
If the problem is an open and they are all different values of polarized electrolytic then you have a simple task of just checking the net result and determining which value is missing (unless however the problem is a short in which case you are back to remove one lead of the caps and testing individually)
simply put if the values are 1 , 2 , 3 , 4 and the resulting measurement is 7, then the 3 or both the 1 & 2 are bad and so on...
==========================================================
Shagalot wrote in message <01bd1d11$0f889220$e641bcca@default>...
Bob
> > Just want to know how can we determine whihc capasitor that fail if all the
> > capasitor are connected together in parralel. What happens if one of the
> > capasitor is shorted, how can we tell which?????
>
> depend on non-ideal behaviour of the connections. You could also just cut
> wires and/or remove parts till you find it. Maybe you should post some
> more details of your homew^H^H^H^H^H problem?
I have used a grid-dip oscillator (GDO) to test capacitors "in-circuit." I just
put a coil of a few turns across the capacitor and use the GDO to determine the
resonate frequency of the combination. The other components connected to the
capacitor will exhibit such a high impedance to the tuned circuit that it will
not significantly alter the resonate frequency. Once the resonate frequency for
the combination is known, the test can be repeated and compared to other
capacitors in the circuit.
Bob
dan
Frank Bemelman wrote:
>
> "Shagalot" <shaga...@hotmail.com> wrote:
>
> >All,
>
> >Just want to know how can we determine whihc capasitor that fail if all the
> >capasitor are connected together in parralel. What happens if one of the
> >capasitor is shorted, how can we tell which?????
>
> > | | | | | | | |
> > c c c c c c c c
> > | | | | | | | |
> >------------------------- Gnd
>
> >Kew
>
> currentlimit at 4-5 amps (to prevent tracks blown off). Now, the smoke
> will tell you where to look. The color of the smoke (grey or blue) is
> not important ;-)
Wow! A sure fire way. But why use a hammer?
Of all the suggestions. The voltage drop method has always
worked best for me. Use a power supply to inject enough current
and you will measure the voltage drop. The trick is to set the
voltmeter to the lowest range and measure the drop between points,
not the voltage from ground to points.
If it's not a dead short, the offending device will get warm enough
you can feel it with your finger. But you shouldn't have to blow
the part off the board to find it.
Best, Dan.
Jan Mourer
>Shagalot (shaga...@hotmail.com) wrote:
>: All,
>:
>: Just want to know how can we determine whihc capasitor that fail if all the
>: capasitor are connected together in parralel. What happens if one of the
>: capasitor is shorted, how can we tell which?????
>:
>: -------------------------- +Vcc
>: | | | | | | | |
>: c c c c c c c c
>: | | | | | | | |
>: ------------------------- Gnd
OkK there are many ways:
Assuming a short:
1) solder them out one by one (use dice),
2) Solder out half of them and test (little math joke :)
3) Aplly Altavox (c)100A current and see the wrong one explode (use only very low voltage of cause))
4) Same as 3 but use few hundred milliamps and check which one gets hot.
5) if its an old set and one is marked Wima remove that one first
6) If they are a bit apart, measure the voltage drops on the tracs, the ones leading to the defective caps
must drop more (then?)
7) supply power and measure the voltage across the caps, probably (use 4 digits) the lowest on is where to look.
8) Remove all of them, good caps do not short, replace all.
9) Gona have a Coce.
J.M.
altavoz
altavoz
Cake . Cheap DMM , one lead as close to cap A pos' term'* , other probe
is touched
to the other similar polarity terminals . You are measuring the polarity
of the current into the shorted cap . If you get some negative reading
and some pos' readings , then keep moving the first probe til it always
has
the neg indication and the other has the pos ind' ( if ur working at
the pos terminals ).
The reason you don't just ground one probe , is the DMM will have far
less sensitivity . We are measuring the voltage drop from
simiular termianls , the lowest volt indicates the shorted cap .
If all the caps are shorted such that the nominal VDC is pulled down
to say .2 vdc , just turn down the supply til it is not cooking
everything
in site and use same method . nix z for email
---------------------------------------------------------------
Kew
Mark E. Nikl
pete...@aol.com (Petercoe) wrote:
>Gee! It would take all of 5 minutes to unsolder one leg of each capacitor.
>Pete...@aol.com
>35 year tv repair
Thats right, as far as that goes, if all are in parrallel and one is
shorted, they would all show a short, so the only way would be to
unsolder each leg
Mark
M&N Electronics