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Author Topic: Testing Resistors  (Read 1627 times)

Capt Podge

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Testing Resistors
« on: March 22, 2012, 01:16:08 AM »

Does anyone know whether a resistor can be tested without it actually being in a circuit ?

Reason being: I think I might have "fried" one while doing a bit of soldering - forgot to put a heatsink in place  :embarrassed: - there is no outward sign of any damage but I found the resistor to be the cause of a circuit failure. Replaced it with a new one and the circuit is working fine - I just wanted to test the culprit before it goes in the SNLR bin

Regards,

Ray.
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More Coffee

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Re: Testing Resistors
« Reply #1 on: March 22, 2012, 01:58:11 AM »

Yes it can..

You'll require a multimeter with an "Ohm" setting..

Check the color bands on the resistor ,once its determined what its value should be, take your ohm meter and using both leads ,,connect one to each end of the resistor..

typically resistors have a gold band..this indicates that the resistor has a tolerance of +/- 10%..

example --- a 1000Ohm (1k) should read between 900 and 1100 Ohm  ..


Hpoe this helps..
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Martin [Admin]

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Re: Testing Resistors
« Reply #2 on: March 22, 2012, 10:04:19 AM »

You will get a wrong value 'in situ', but if the reading is More than the colour band value, must guess it has blown.
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dodgy geezer

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Re: Testing Resistors
« Reply #3 on: March 22, 2012, 10:17:55 AM »

It depends on so many things that it may be of little value to make a generality, but resistors are pretty resistant to heat damage, and it's hard to cook one. I would expect to see paint damage on a heat-damaged resistor. Maybe the problem was with the solder joint, and so re-soldering was what cured it?
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malcolmfrary

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Re: Testing Resistors
« Reply #4 on: March 22, 2012, 06:05:30 PM »

The only way a resistor can be tested is out of circuit, if its in circuit you will be measuring all of its mates.
Most two legged components consist of a former, the electric bits draped on the former, and an end cap or similar at each end that the wires fix to.  Overheating can create a dry joint at the end cap.  Using a heatsink is normally the prime way to cook a component - the heatsink actually stores unwanted temperature and if not removed very quickly acts to continue heating the component.  Been there, got the badge.  A firm mounting, good lighting, hot iron, and if unsoldering, a good solder sucker are vital for the speed needed.
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Capt Podge

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Re: Testing Resistors
« Reply #5 on: March 24, 2012, 10:27:41 PM »

Thank you all for your comments / observations on this one.

Seems to have been as Dodgy geezer suggested - found to be a dry solder joint after all - DOH !

anybody out there got any handy tips on soldering ? {-) {-) {-) {-) {-) :embarrassed:

Regards,

Ray.

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malcolmfrary

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Re: Testing Resistors
« Reply #6 on: March 24, 2012, 10:45:01 PM »

Plenty of discussions on the forum, just a search away, but -

Cleanliness
Hot* iron, preferably carrying a FILM of liquid solder.
Cleanliness
Good solder with flux core
Clean tinned surfaces
Speed (fast in, fast with solder, fast away, fast to blow on it to cool it down before the heat wanders off)
Clean any flux residue.
Practice.

If I forgot to mention it, everything has to be clean.
*hot = so that when the solder is touched to the tip, it melts INSTANTLY and gives off a puff of flux smoke.  Sulky melting is bad.
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Circlip

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Re: Testing Resistors
« Reply #7 on: March 25, 2012, 10:05:09 AM »

Keep throwing this one in, look round for a multicore solder (used to be "Ersin") that has a Lead content not the new Euronannysafe Leadless. 60/40 is  the weapon of choice.

  Regards  Ian.
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ACTion

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Re: Testing Resistors
« Reply #8 on: March 25, 2012, 12:16:57 PM »

Keep throwing this one in, look round for a multicore solder (used to be "Ersin") that has a Lead content not the new Euronannysafe Leadless. 60/40 is  the weapon of choice.

  Regards  Ian.
PM sent. I still have some smaller reels of similar stuff if you're interested. We can't use it unfortunately  <:(
DM
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CF-FZG

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Re: Testing Resistors
« Reply #9 on: March 25, 2012, 06:22:34 PM »

We can't use it unfortunately  <:(
DM

Which is a bit daft Dave, because in aviation it's all you are allowed to use >>:-(
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wibplus

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Re: Testing Resistors
« Reply #10 on: March 29, 2012, 10:12:21 PM »

PM sent. I still have some smaller reels of similar stuff if you're interested.
DM

Interested.  :-)) I been trying to find some.  :-)
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