caps that have a short

Spectre

Administrator
Staff member
Jnr Admin
Joined
Jun 3, 2001
Messages
40,891
Reaction score
5,166
Location
Airstrip One
Meter set to low Ohms range or Continuity depending on meter.

Box powered off.

Put a probe at each end of the capacitor.

Some inductors look like caps too, they will show low Ohm readings.
 

Spectre

Administrator
Staff member
Jnr Admin
Joined
Jun 3, 2001
Messages
40,891
Reaction score
5,166
Location
Airstrip One
Lololol

David asks question 17-10-2005, 04:52 AM and I answer 16-10-2005, 11:52 PM.

My post is at the top as it's asked first temporally here, but it's a different time in his dimension.

More psilocbye anyone?
 

intel131

Inactive User
Joined
Oct 8, 2005
Messages
61
Reaction score
0
I throught that to test a cap it has to be out of the circuit?
 

chookey

VIP Member
VIP Member
Joined
Oct 6, 2005
Messages
5,012
Reaction score
3,694
Location
nr.Cov.... pure n*l
To test for shorts you are using the correct range on your multimeter.Connect your leads straight across the cap, no power applied, try to discharge any voltage on the cap as well. It is pointless connecting the black to ground as the majority of electrolytics will have a ground connection anyway. Polarity doesn't matter when checking for a short. Capacitors going short is very rare,they tend instead to go open or leaky. Bear in mind that a capacitor might read ok, even with a capacitance meter, cos it is breaking down when voltage is applied. Only safe bet if you don't have an esr meter is to test by replacement.
Good luck
 

Spectre

Administrator
Staff member
Jnr Admin
Joined
Jun 3, 2001
Messages
40,891
Reaction score
5,166
Location
Airstrip One
intel131 said:
I throught that to test a cap it has to be out of the circuit?
Lots of the SMT caps on mainboards of Pace units are between a supply or bus line and ground: none of those should show a low resistance to DC in circuit as the semiconductor connected end should be a high impedance path to ground.

It is also possible to test caps in circuit under other circumstances.
 

Spectre

Administrator
Staff member
Jnr Admin
Joined
Jun 3, 2001
Messages
40,891
Reaction score
5,166
Location
Airstrip One
chookey said:
Capacitors going short is very rare,they tend instead to go open or leaky.
With SMT caps the most common fault is going short.

Open or leaky is opposite ends of the scale to each other almost.
 

chookey

VIP Member
VIP Member
Joined
Oct 6, 2005
Messages
5,012
Reaction score
3,694
Location
nr.Cov.... pure n*l
sorry, should have kept out of this one.I was a tv engineer for a number of years. Working with capacitors you could hold in your hand and know it was there. Only ever came across 1 short circuit capacitor (electrolytic) in that time.
 

Spectre

Administrator
Staff member
Jnr Admin
Joined
Jun 3, 2001
Messages
40,891
Reaction score
5,166
Location
Airstrip One
chookey said:
sorry, should have kept out of this one.I was a tv engineer for a number of years. Working with capacitors you could hold in your hand and know it was there. Only ever came across 1 short circuit capacitor (electrolytic) in that time.
Someone gave me a box of some older electrolytic caps a while ago, big ones. Went on eBay to a radio enthusiast for £3. They did smell quite nice as they hadn't dried out as had been kept in jars :) .

That will be a fault for cable boxes soon, elecs drying out and going open as you say :).
 

davidh

<font color="RED">Administrator</font>
VIP Member
Joined
Aug 9, 2001
Messages
14,954
Reaction score
121
Location
LIVERPOOL
may sound silly
but what do u set the multimeter to to check for shorts
i have set mine up for continuity black on earth and red on either side of the cap
is this right??
if not how do i check
asking this cos i have checked caps for low or no signal
and some have continuity on both sides some dont
 
TEST
Top