VOM Question

[AlterEgo99 5,000+ posts]

Well, I thought I new the basics of operating a voltmeter but a few terms have me confused and I am SURE someone can help. //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

First, here is a direct quote:

"To check for a good ground reference, take a volt-ohm meter (VOM) and measure the resistance between the chassis of the radio and the shield of the RCA line level outputs of the radio. This reading should indicate a direct short."

How should I set my digital VOM to perform the above action?

Second, does anyone know what a "ground sniffer" is? Do you really need one or can a good ground point be determined simply from a VOM?

I'm attempting to troubleshoot an alternator whine problem and am going to be trying to determine the source step by step.

Thanks!

Click to read more...

 

[SicAudio 5,000+ posts]

do you know how to set it for ohms? do that and touch the leads together. the reading you get ( 0.0 or close to it ) is the same reading you should get when you check for a good ground. ground sniffer is not needed your vom aka dmm is just fine.

 

[AlterEgo99 5,000+ posts]

Yup, I know how to set it for ohms. Any particular setting or does it matter the size of resistance? I'm assuming that once set I simply connect one lead to the ground wire and another to the chassis ground location and if it comes up all zeroes it is a good ground point. If it doesn't, then I should try some other location. Have I got that right?

Also, when checking the shield portion of the RCA line level outputs I am assuming this is the outer portion of the RCA jack?

 

[SicAudio 5,000+ posts]

yes and yes you know exactly what to do //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif GL

I usually use w/e is lowest.

 

[AlterEgo99 5,000+ posts]

Awesome, thanks man!

The infamous alternator whine is always such a fun thing to try and troubleshoot.

Oh yeah, one other quick question. I would like to check the speaker wires for any possible grounding short. I was planning on doing this from the amp location versus tearing the truck all apart, again. I take it that I can take the similar approach to test this using the VOM?

 

[JimJ 5,000+ posts]

Measure the resistance between the positive and negative leads //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[SicAudio 5,000+ posts]

exactly, just test for continuity to ground //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif you know more than most so I am sure I dont have to explain that lolz.

 

[SicAudio 5,000+ posts]

Measure the resistance between the positive and negative leads //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

if he measures resistance he will get coil resistance not speaker short to chassis.

 

[AlterEgo99 5,000+ posts]

if he measures resistance he will get coil resistance not speaker short to chassis.

OK, gettin' a bit confuzzed here...can you "simplify" what I need to do to test for a speaker short at the amp end? If I know what to set the VOM at and where to place the leads (and what to look for on the output) I should be good to go.

Thanks!

 

[AlterEgo99 5,000+ posts]

Never mind, think I've got it! //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

Set VOM/DMM to Ohms, place one lead on the positive (+) wire and the other lead on the negative (-) wire and observe the reading, which should be close to the ohm rating of the speaker. For example, for a 4 ohm speaker I should see something close to that number, say 3.55.

I'm curious what I will see when performing this on a component speaker where the wire from the amp runs to a crossover where the signal is split between the woofer and the tweeter. Should I still expect to see the rated ohms?