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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 1:24 pm 
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To test a meter, you have to pass current through it.** The test with a battery and a resistor does that. Also, you mentioned getting a response when you used your meter to measure one of the terminals---this means that your meter was drawing enough current to get a response from the meter.

Testing the switch:
It is a DPDT configuration. The poles connect to the meter. Each pole is switched between 2 other contacts. So, use an ohmmeter to measure the resistance from a pole to the other contacts as you operate the switch.
Here is a nice summary of switch types:
http://musicfromouterspace.com/analogsy ... sembly.pdf



** For any 2-terminal passive device, you can do a DC test in several ways:
--measure the resistance
--apply a voltage and measure the current
--apply a current and measure the voltage

In the case of a meter, you would also be watching for needle movement.

The details of the test depend on what the device is---meter movements can be very sensitive, meaning that a small current will cause the meter to respond. Too much current can damage the meter. Thus, if you don't know the sensitivity, you need to start with something like 1 microamp. (eg 1.5 volts in series with 2 megohms would give you 0.75 microamp.)

No matter what method you use, you have to create a complete circuit in which current passes from a source, through the device being tested, and back to the source. If this does not make sense to you, then do some reading on basic electric circuits.

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 1:31 pm 
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So from my sketch is the meter switch is hooked up properly? The meter has 2 jewels marked on the back.


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 1:57 pm 
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spsquires wrote:
So from my sketch is the meter switch is hooked up properly?
What does the schematic say? From your sketch, it looks like a typical "reversing switch"--depending on the switch position, the flow of current through the meter changes direction.

Quote:
The meter has 2 jewels marked on the back.
I have no idea what that means---are you saying it is marked "2 jewels"? Regardless, it does not tell us the full-scale current. (I previously described what to do if you don't know what the meter sensitivity is...)

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 6:03 pm 
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I disconnected both wires from meter and measured the resistance and it shows a short.


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 7:48 pm 
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..........smh

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 7:58 pm 
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If you are going to write something put it in a sentence. Not everyone understands your English.


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 11:08 pm 
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spsquires wrote:
I disconnected both wires from meter and measured the resistance and it shows a short.

That is quite a non-sequitur from what I was asking / suggesting!!

Did you observe if the meter responded? If not, don't do it again--you could damage the meter.
What I have tried to convey is that you have to test a meter with a current low enough not to cause damage. This is why I asked if the meter was labelled---and IF NOT--suggested starting with something less than 1 microamp. I don't know what the current from your DMM might be when checking resistance.

So--if the meter DID respond, then we can continue with the other things already discussed.....

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Tue 12, 2019 11:30 pm 
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The meter did not respond and I took it apart and the spring like piece of wire is dislocated from where it was and looks like it was overheated. So either way it is now garbage. My next problem is finding another meter.


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Wed 13, 2019 4:18 pm 
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My impression is that you did not understand a lot of my advice on this one. It is conceivable that you caused the meter to fail when you tested it with your ohmmeter. If the meter winding shows continuity**, it could still be OK.....and the mechanical issue could maybe be fixed.
The next time you have to test a meter, use a controlled (small) current, as I recommended earlier.

Perhaps the most important lesson from this thread:
--Read all of the comments and suggestions---and respond to them.
--If you don't understand something, ask.

**"continuity" means that current is flowing in the circuit. A "short circuit" means the resistance is substantially lower than it should be. When measuring small resistances, be sure that you are on the lowest range of your meter, and that you know what it reads when the two test leads are connected. (Mine reads ~ 0.2 to 0.3 ohms----If I need an accurate measurement of a very low resistance, I use my impedance bridge.

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Wed 13, 2019 4:51 pm 
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Where would one measure the winding from now?


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Wed 13, 2019 5:20 pm 
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I think it's time to review basic measurement concepts, The following assumes basic DC measurements, but the basic ideas apply to AC also.

1. To do any meaningful measurements, you have to understand that current flows in a closed loop from source, through the loads, and back to the source. Along the way, there are changes in voltage based on the properties of various components.

2. Voltage is either measured with respect to a common reference point---eg the "chassis ground", or the return side of a power source---OR: it is measured across a specific component---e.g. the "voltage drop" across a resistor.

3. Current is measured in a specific circuit branch--with the meter placed in series.

4. Measurement of resistance can be done in 2 basic ways:
--apply a known voltage, and measure the current
--apply a known current, and measure the voltage
In either case, one must assure that the levels are compatible with what is being measured. As an absurd example, you would not measure the resistance of a 5-ohm resistor by applying 500 volts and measuring the current.
The important point here is that you have to know how your meter measures resistance whenever you are testing something that is very sensitive.

5. A resistance measurement on a 2-terminal device (eg a resistor or coil) is normally from one side (terminal) to the other. However, it is sometimes also important to test from one of the terminals to the package or housing. For example, when evaluating a transformer, you need to measure the resistance of each winding (which is a "2-terminal device") AND the resistance from the winding to the transformer structure.

6. Be sure you understand how your meter responds in various situations: For example, when measuring resistance, be sure you use the lowest scale that gives a reading. With many (most?) meters, a 5-ohm resistor measured on the 20Kohm scale will measure as zero.

7. Know what to expect: Using the service information, or basic theory, you need to know what SHOULD be there before trying to measure it...
--is it AC and DC--or both
--high voltage?
--sensitive element that might be damaged by excessive current.

8. Lastly, measurements will always be problematic if you are not clear on basic principles---as a minimum: Ohm's Law and Kirchoff's current and voltage laws.

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Wed 13, 2019 9:50 pm 
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Probably a better question is the windings wire or something else? Maybe I misunderstood but also I asked questions that I did not get answered also.


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Thu 14, 2019 12:17 am 
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After scanning through this thread I see no value in continuing on and destroying a valuable piece of test equipment. I would suggest putting this tester away before you do more damage. You cannot simply test meters and other parts without knowing how they work and what they do in the circuit. You have to know how the circuits in the tester work and how to troubleshoot them. You will have to gain more electrical knowledge to continue with this repair. This is probably something you do not want to hear, but years from now you will thank me for it.

Dave


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Thu 14, 2019 2:47 am 
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spsquires wrote:
Probably a better question is the windings wire or something else?

All about meters:
https://www.allaboutcircuits.com/textbo ... s-a-meter/

EDIT:
I had pasted in the wrong link---fixed

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Thu 14, 2019 2:19 pm 
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I put the wrong link in my last post----now fixed.

There are many other articles about the basic construction of meters.

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Fri 15, 2019 12:37 pm 
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Did some research and looking at inner workings of needle assembly and there was one side of the assembly that had a spring like piece of wire attached to end of needle that was attached to one side of coil that was burnt like and broken off. This piece of spring like wire was fixed I think needle would work. So how does one fix this piece?


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Fri 15, 2019 12:52 pm 
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We would need some good pictures to understand what all the parts are.

Did you verify that the meter coil is OK?

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Fri 15, 2019 2:38 pm 
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pixellany wrote:

Set up a 1.5 volt battery with a series resistor to supply less than one half of the full-scale current.
Example: full scale 10uA----for 5uA, the series resistor will be 1.5 / 1E-5 = 1.5E5 (150Kohms)

.


Mark,is it just me ,or did you goof and actually calculate the resistance for 10uA instead of 5uA(half-scale)?I'm thinking it should be 300Kohms for half-scale?

Writing the numbers out instead of using scientific notation may make things a whole lot clearer for Mr. Squires,and others,as well.


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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Fri 15, 2019 2:42 pm 
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Yes---good catch!!

To get 0.000005 Amp, Use 1.5 Volts and 300,000 Ohms. Better??

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 Post subject: Re: Starkit model 12-22a
PostPosted: Mar Fri 15, 2019 2:59 pm 
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pixellany wrote:
Yes---good catch!!

To get 0.000005 Amp, Use 1.5 Volts and 300,000 Ohms. Better??


Yes,thanks.

I'd embarrass myself to admit to how long it took me to figure out that you were using scientific notation,but I haven't even thought about it since tech school,and that was a loooooong time ago. :wink:


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