How can i tell if i have a short in circuit board

[ricosavy]

I know these may should sound simple to some but lately i have been confused by this.For example i measured a cap on the positve to ground pad on board and i get 46 to 47 ohms is this considered a short or is this normal.I am just trying to figure what is considered a short and what is not so i wont waste hrs trying to track something that is normal and not a short.any help would be appreciated. Thanks

[999999999]

Re: How can i tell if i have a short in circuit board

You often can't measure for a short in a specific component by leaving it soldered to the circuit board when making a reading as it will give a misleading measurement.

However, by measuring 46 to 47 ohms you have at least confirmed that the capacitor is not shorting out, but you have not (yet) confirmed that the capacitor isn't excessively leaky nor that it remains non-shorted if the temperature changes.

Capacitors don't generally short long enough to allow this kind of investigation without venting if not exploding worse than that.

Investigation of a circuit usually starts by thinking about what kind of circuit it is, what it needs to do, where it needs to do it, and what types of measurements to make in the order of the most likely components to fail first, also taking visual cues and if necessary, probing for expected voltage or signal levels while the circuit is live (but that's more dangerous if not familiar with the risks).

Some people will also investigate whether the product has a known excessive failure rate or common failure mode and discovery of what others have done about that.

It is hard to generalize about something like this except that many components need to be removed from the circuit for a good reading. Different situations may make a different analysis sequence more advantageous.

[budm]

Re: How can i tell if i have a short in circuit board

That capacitor may have other components connected in parallel with it also.

[rievax_60]

Re: How can i tell if i have a short in circuit board

It might be a resistor purposely placed across the rail to provide a minimum load for the power supply.

[ricosavy]

Re: How can i tell if i have a short in circuit board

The reason i asking is that my esr meter shows a short when test cap but when i pull cap the cap is good and i can place a ohm meter on pads and it will give me the same reading without cap in circuit. Making me think there is short but reading being 46 ohms would that be concerned a short.or does resistance have to be way lower to be a short.

[cheapie]

Re: How can i tell if i have a short in circuit board

The reason i asking is that my esr meter shows a short when test cap but when i pull cap the cap is good and i can place a ohm meter on pads and it will give me the same reading without cap in circuit. Making me think there is short but reading being 46 ohms would that be concerned a short.or does resistance have to be way lower to be a short.

That's probably a resistor in parallel with it.

[budm]

Re: How can i tell if i have a short in circuit board

You have to trace out where the positive leg of the cap is connected to. How the cap is used in the circuit must also be considered.

[ricosavy]

Re: How can i tell if i have a short in circuit board

I will study the schematics more to see how component is used .I though If there was some low resistance of 60 ohms and below I had a short but after testing a few boards just seem that some I though were shorts just seem normal.

[ricosavy]

Re: How can i tell if i have a short in circuit board

Looking at the schematic i removed cap c132 when i measure the cap in circuit i get 46 ohms with cap removed i still get 46 ohms testing pads where it was soldered.i have also removed d102 ,c134 and chip i105 ap1533/ap1534 and i still get 46 ohms on pads c132 . the only one i have not removed is cap c135 100nf becuase it is small. I dont see a resistor that would give me that resistance does it look like a still have a short or is the normal on this schematic.

[ricosavy]

Re: How can i tell if i have a short in circuit board

Another pic

[ricosavy]

Re: How can i tell if i have a short in circuit board

Here is the cap i have not removed i circled the cap it is a 100nf cap

[rievax_60]

Re: How can i tell if i have a short in circuit board

Is the rail still connected to what it normally powers?

[ricosavy]

Re: How can i tell if i have a short in circuit board

Right now the board is out of the tv

[rievax_60]

Re: How can i tell if i have a short in circuit board

I would expect a 1.2v regulator like that to be at Point OF Load, near the IC that it powers.

[ricosavy]

Re: How can i tell if i have a short in circuit board

When i had the board in tv and powered up i do remeber checking voltage on pin 5 and 6 and output was close to 1.2 v

[rievax_60]

Re: How can i tell if i have a short in circuit board

I would say that there is no problem in that area.

[ricosavy]

Re: How can i tell if i have a short in circuit board

Ok i will move on to check other things once i resolder all caps and chip back on thanks for help i did think i had another short but after reading the other post i found a 75 ohm resistor in parallel with diodes so that told me there was no short.know i realize that there is no short since i am getting the right output 1.2 v .all these has made me realize if i look more closer at schematic i will be able to tell if a circuit is working right and not to over complicate things.thanks for everyones input.thanks rievax_60

[ricosavy]

Re: How can i tell if i have a short in circuit board

well i got a leakseeker 89 it arrived today so when i do get into a short i can find it easier hopely it was a good investment.