Testing Caps and Resistors...

Darkstrike · #1 08-31-2009, 01:14 AM

Is it possible to find out what they are, if I have some, using a multimeter.

I have a few old circut boards, with bunches of them on it, and want to find out if any of them could be used to do some mods to my basses, like Greasebucket tone circuts, or should I just dump 'em.

UncleFluffy · #2 08-31-2009, 01:44 AM

When I was in high school I stripped old computer boards using a blowtorch and a hammer (run the torch over the back of the board to melt the solder then hit it with a hammer - all the good stuff falls out onto the bench - if you do this, make sure there's good ventilation). Got lots of chips that way, most of them still worked afterward.

For just Rs and Cs I wouldn't bother - they tend to be very cheap components and not worth your time unless you're looking for something very specific and vintagey.

Darkstrike · #3 08-31-2009, 01:50 AM

I wouldn't bother, but there's no local store that carries caps and resistors, and I have limited access to buying stuff online.

rcarraher · #4 08-31-2009, 01:57 AM

Quote:

Originally Posted by Darkstrike

Is it possible to find out what they are, if I have some, using a multimeter.

I have a few old circut boards, with bunches of them on it, and want to find out if any of them could be used to do some mods to my basses, like Greasebucket tone circuts, or should I just dump 'em.

Well, on resistors, they have a color code. But you'll figure them out with an ohm meter, but you'll want to decipher the color code to see that they match up. Capacitors can't really be tested or ID'd with an ohm meter except for dead short. You can "kind of" test them with an ohm meter by setting to a midrange resistance and putting the leads on each end of the cap. It should start out reading a mid-low range ohmage and start "counting up" or getting more and more resistance until it may reach infinity. This effect is because an ohm meter applies a control voltage to read resistance. When placed across a cap, it slowly "charges" the cap (which has the ability to hold a DC voltage charge) As the cap charges, it gains resistance. If you reverse the leads you see the same thing again. All this means is the cap still has capacitance. Not necessarily in spec, but it is still functioning as a cap.You need a capacitance meter to tell if it is functioning right. Caps also have a "code" telling us what it should be. Some caps will have a color code that is different than a resistor, others will have a series of 3 or 4 numbers. This, with being able to recognize what the cap is made of tell us how to read the value.

In both cases, test the parts out of the circuit, neither reading is going to be accurate in circuit.

Anesthesia · #5 08-31-2009, 02:00 AM

if your multimeter has a symbol that looks like this -l l- that is for testing caps and it will display its value. caps are polarized so one way you should get no reading swap the probes and you will get a reading.

and put it on ohms or Ω and it will tell you the resistance value.

and for good measure this is for testing diodes ->- diodes are also polarised. reading one way not the other.

UncleFluffy · #6 08-31-2009, 02:01 AM

Quote:

Originally Posted by Darkstrike

I wouldn't bother, but there's no local store that carries caps and resistors, and I have limited access to buying stuff online.

What do you need?

Darkstrike · #7 08-31-2009, 02:01 AM

Quote:

Originally Posted by rcarraher

Well, on resistors, they have a color code. But you'll figure them out with an ohm meter, but you'll want to decipher the color code to see that they match up. Capacitors can't really be tested or ID'd with an ohm meter except for dead short. You can "kind of" test them with an ohm meter by setting to a midrange resistance and putting the leads on each end of the cap. It should start out reading a mid-low range ohmage and start "counting up" or getting more and more resistance until it may reach infinity. This effect is because an ohm meter applies a control voltage to read resistance. When placed across a cap, it slowly "charges" the cap (which has the ability to hold a DC voltage charge) As the cap charges, it gains resistance. If you reverse the leads you see the same thing again. All this means is the cap still has capacitance. Not necessarily in spec, but it is still functioning as a cap.You need a capacitance meter to tell if it is functioning right. Caps also have a "code" telling us what it should be. Some caps will have a color code that is different than a resistor, others will have a series of 3 or 4 numbers. This, with being able to recognize what the cap is made of tell us how to read the value.

I see, thanks for all the info.

Oh, and FWIW, is this the kind of meter I want for working on basses and guitars?
http://www.argos.ie/webapp/wcs/store...&Submit=GO+%3E

Anesthesia · #8 08-31-2009, 02:04 AM

that meter will do just fine but all you need is an el cheapo that does dc volts, for testing batteries etc, resistance, capacitance, and diode check, just about every meter will have these functions.

Darkstrike · #9 08-31-2009, 02:05 AM

Quote:

Originally Posted by UncleFluffy

What do you need?

I don't actually know yet, I'll have to look into the different mods that can be done.

rcarraher · #10 08-31-2009, 02:05 AM

Quote:

Originally Posted by Anesthesia

if your multimeter has a symbol that looks like this -l l- that is for testing caps and it will display its value. caps are polarized so one way you should get no reading swap the probes and you will get a reading.

and put it on ohms or Ω and it will tell you the resistance value.

and for good measure this is for testing diodes ->- diodes are also polarised. reading one way not the other.

Not all caps are polarized. If it doesn't have a + on one end and a - on the other, is a ceramic or non elctrolitic type cap.

Darkstrike · #11 08-31-2009, 02:06 AM

Quote:

Originally Posted by Anesthesia

that meter will do just fine but all you need is an el cheapo that does dc volts, for testing batteries etc, resistance, capacitance, and diode check, just about every meter will have these functions.

I see, cheers, this is the only one I can get locally, and as I'm buying a new soldering iron from the shop anyway, I might as well go for it, since it will work.

Anesthesia · #12 08-31-2009, 02:08 AM

Quote:

Originally Posted by rcarraher

Not all caps are polarized. If it doesn't have a + on one end and a - on the other, is a ceramic or non elctrolitic type cap.

you are correct sir. also they may not have a plus or minus one side of the barrel of an electrolytic cap may have a line running the length of the body this shows the - leg.

rcarraher · #13 08-31-2009, 02:10 AM

Quote:

Originally Posted by Darkstrike

I see, thanks for all the info.

Oh, and FWIW, is this the kind of meter I want for working on basses and guitars?
http://www.argos.ie/webapp/wcs/store...&Submit=GO+%3E

Thats a pretty nice meter, and it does have a capacitance test built in. Usually, these are adequate for hobbiest needs and accuracy. I'm an electronics engineer, so naturally my meters are are all over kill but that a real nice meter. If you just want to futz around with basses I don't know if you guys have a Radio Shack over there, but they have a decent meter for about $30-40 dollars that would be more than adequate. I haven't done the conversion, but 40 euros sounds high.

rcarraher · #14 08-31-2009, 02:13 AM

Quote:

Originally Posted by Anesthesia

you are correct sir. also they may not have a plus or minus one side of the barrel of an electrolytic cap may have a line running the length of the body this shows the - leg.

Yup, then there are electrolytics that are non polarized. Usually say NP on them somewhere. BTW, you are talking to an electronics engineer. U of Maryland, class of 76.

Anesthesia · #15 08-31-2009, 02:15 AM

yeah im in the same boat as rcarraher. im a sparky and have a meter worth a few hundred australian dollars. it is a multimeter/clamp meter that measures up to 1000Vdc so its deffinately overkill for bass work. the major difference between cheap and expensive meters is the accuracy of the measurement (cheap will still be accurate) and the speed at which it reads and displays changes but you wont need anything elaborate for checking small voltages or testing resistors diodes etc.

Darkstrike · #16 08-31-2009, 02:18 AM

Quote:

Originally Posted by rcarraher

Thats a pretty nice meter, and it does have a capacitance test built in. Usually, these are adequate for hobbiest needs and accuracy. I'm an electronics engineer, so naturally my meters are are all over kill but that a real nice meter. If you just want to futz around with basses I don't know if you guys have a Radio Shack over there, but they have a decent meter for about $30-40 dollars that would be more than adequate. I haven't done the conversion, but 40 euros sounds high.

We have no Radioshacks, sadly, I'd be constantly in there if we did!

And indeed, all I'll be doing is futzing around with basses, maybe the odd guitar. Seeing that its pretty nice, I'm not too worried about the 40€ I'm just glad its not more expensive, to be honest.

UncleFluffy · #17 08-31-2009, 02:58 AM

Quote:

Originally Posted by Anesthesia

the major difference between cheap and expensive meters is the accuracy of the measurement (cheap will still be accurate) and the speed at which it reads and displays changes.

Those + how long it lasts before it randomly craps out on you without any apparent reason why.

(The one the OP posted doesn't look too bad though).

rcarraher · #18 08-31-2009, 03:03 AM

Quote:

Originally Posted by Darkstrike

We have no Radioshacks, sadly, I'd be constantly in there if we did!

And indeed, all I'll be doing is futzing around with basses, maybe the odd guitar. Seeing that its pretty nice, I'm not too worried about the 40€ I'm just glad its not more expensive, to be honest.

Well, 40 euro (How do you make that funky E) is probably okay, but I'm thinking for what I think is about $70 you could probably get a real decent used Fluke with the same features. Fluke is the Cadillac of meters. But, that one will probably be more than enough. If you have questions about how to use it, feel free to PM.

Darkstrike · #19 08-31-2009, 03:10 AM

Quote:

Originally Posted by UncleFluffy

Those + how long it lasts before it randomly craps out on you without any apparent reason why.

(The one the OP posted doesn't look too bad though).

Ugh, I hate it when stuff like that happens, like my Peterson tuner.

Quote:

Originally Posted by rcarraher

Well, 40 euro (How do you make that funky E) is probably okay, but I'm thinking for what I think is about $70 you could probably get a real decent used Fluke with the same features. Fluke is the Cadillac of meters. But, that one will probably be more than enough. If you have questions about how to use it, feel free to PM.

40€(I hold the AltGr button, and press 4 for the dollar sign) is just about $57, I can see the Fluke would be much better, but as you said, I don't need it for anything major, testing pickups, caps and resistors, making sure shielding is good, that kind of stuff.

And cheers for the offer helping me with how to use it.