Cheap component tester/Oscilloscope

[Script]

That's a lot of Bourbon.

Can't really see details. Worth a try in situ. Also check legends on caps, both sides. The caps should tell you what they are. One says 104 (=100nF).

That charred thing on the left, only *tried* to melt? Looks bad. What is that?

 

[Brian Roth]

That's a lot of Bourbon.

Can't really see details. Worth a try in situ. Also check legends on caps, both sides. The caps should tell you what they are. One says 104 (=100nF).

That charred thing on the left, only *tried* to melt? Looks bad. What is that?

My hunch is it's an inductor. Might not get a "good" readout of value regardless of the type of test instrument if turns are shorted.

Bri

 

[MicMaven]

My hunch is it's an inductor. Might not get a "good" readout of value regardless of the type of test instrument if turns are shorted.

Bri

Good Evening @Script and @Brian Roth -- YES, that is an inductor. And, Yes, my worry is exactly as you state, i.e., that it has lost its original value being shorted somewhere along the coil. The manufacturer is playing its cards close to the vest, and charges a mere $22 plus $13 shipping for just one inductor and one capacitor - both of which seem to be different values from the original. Not much help.

My research indicates a 2.8 uH value is appropriate. As Mr. Script suggests, the capacitors are clearly marked, which validates the meter reading, leaving only the inductor in doubt.

But the take away seems to be .... (drum roll) ... it is usually best to measure such parts off board if possible. THANKS for the leg up, gents. James

 

[abbey road d enfer]

You can probably identify the capacitors by reading their markings, and the other component, as Brian noted, may be an inductor. With the LCR tester, you may have a good reading, or not.
Anyway you would need to lift one leg.
OTOH, the values are not critical at all. For the inductor, the only constraint regarding its value is that its reactance be significantly higher than 50 ohms within the operating range.
It would be interesting to find out why it seems to have overheated.
These things have a rated power.

 

[abbey road d enfer]

THE PRODUCT DESCRIPTION SAYS:
- Modle:LC200A.
- Supply power: +5v ,miniUSB interface ,4pcs AA battery (NOT included).
- Measurement accuracy:1%.
- Capacitance measuring range: 0.01 pF - 10uF.
- The minimum resolution: 0.01 pF.
- Big Capacitance measuring range1uF-100mF/minimum resolution:0.01UF.
- Inductance measuring range: 0.001 uH - 100mH.
- Big inductance measuring range: 0.001 mH - 100H.
- The minimum resolution: 0.001uH.
- Test frequency range: L/C about 500KHZ/Big inductance 500HZ.
- Effective display digits: 4 digits.
- LCD display mode: 1602.
- Size:15cm x 9cm x 3.5cm - 5.91inch x 3.54inch x 1.38inch.

James

Well, there's a metrologic issue there.
The person who wrote the specs made a confusion between resolution and precision.
Although the unit is capable of displaying with 0.01 resolution, it doesn't mean that it's capable of properly measuring 0.01.
As rock soderstrom mentioned earlier, capacitors below 50pF result in unreliable values.

 

[MicMaven]

You can probably identify the capacitors by reading their markings, and the other component, as Brian noted, may be an inductor.

Um ... er ... this sorta puts me on the spot! And, I do not wish to "pull rank" ...

I greatly appreciate the input, and I do not wish to appear argumentative, but there is no doubt IT IS (and should be) an inductor! My ONLY question is whether I can measure the component accurately without lifting a leg or removing it entirely from the circuit.

SIDEBAR COMMENT -- For reference, this is a DC bias tee injector circuit that powers a remote device over RF coaxial cable (e.g., LMR-400 or RG-9913). It uses a capacitor and inductor to inject 12v DC coax transmission line, while blocking DC from entering a very sensitive HF/UHF/VHF receiver. The second capacitor is a belt-and-suspenders protection keeping DC from going where it does not belong. The capacitor values are both clearly marked, but I wanted to test them to verify they retain their marked values. I suspect Mr. @Brian Roth correctly guesses the inductor may be damaged and no longer presents its original value. Parenthetically, there is an equal but opposite bias tee device at the far end of the coax transmission line, powering a remote automatic impedance transforming network.​

​

A sample schematic is attached for reference. The first one is a conceptual schema, while the second one is a draft of what I plan to build, myself. It is about a simple as it ever gets! ​

Thus, the ONLY question is how to properly use the meter to verify whether my original unit has suffered damage or not.

Happy trails to all. James / K8JHR

 

[MicMaven]

The person who wrote the specs made a confusion between resolution and precision.

Understood!

And much the pity, but that is endemic to buying cheap products on eBay, where we can only hope vendors provide accurate specifications and instructions. I am frequently amazed at how far off the mark product descriptions can be on eBay. Sometimes we must be code-breakers to make sense of it - not to mention the number of outright misrepresentations found therein. You may recall a previous thread about "metal" U87-style bodies with noise canceling circuits which are, in fact, made of plastic and lack any sort of DSP noise cancelation circuit as claimed in the Seller's product description.

Perhaps we could acquire a more accurate understanding of the LC Meter's actual capabilities by reading multiple descriptions from multiple vendors, hoping to separate the wheat from the chaff, as it were. I don't suppose they have all gotten it wrong ... or have they?

Crazy eh? Much appreciated! James

 

[abbey road d enfer]

Thus, the ONLY question is how to properly use the meter to verify whether my original unit has suffered damage or not.

Well, if you let it as is, you'll have some leakage capacitance, which may or may not alter the measurement. Since the measurement is done at 500kHz, I don't think it matters much.
Just make sure that nothing is connected to the SMA connectors.

 

[MicMaven]

Well, if you let it as is, you'll have some leakage capacitance, which may or may not alter the measurement. Since the measurement is done at 500kHz, I don't think it matters much.
Just make sure that nothing is connected to the SMA connectors.

ROGER! Thank you. - James

PS - I am struck by how much the original injector varies from so many others I have researched. Other examples have values all over the map, and beyond, so while the circuit is a fairly common theme, there is no consensus as to values to accomplish the task. The values in my proposed draft schema reflect those found in what I consider higher quality devices. Putting multiple caps with different values in parallel and multiple inductors with different values in series seems a better approach (to manage different frequency ranges) at least that appears to be the case as I study competing circuits. Still I am struck by the big variation in component values for such a simple circuit when all of them are doing essentially the same thing! I guess it would not be interesting if it were too easy!

Thanks again. All valuable assistance. - James

 

[abbey road d enfer]

The thing is these are made to cater for a large frequency range. With a simple design, it's impossible to optimize it for all possible needs.
Basically they're compromises, and one's compromises may be different than someone else's.
I would say the best solution is to have it optimized for the preferred frequency range.

 

[Gold]

Both of my PEAK LCR meters started reading the same pf amount no matter the cap. One of these cheap testers arrived today. I’m looking forward to putting it to use.

 

[Gold]

Well, I did a few dummy measurements to make sure it worked. Then I was ready to test the caps I needed to test. I didn't discharge them and destroyed the meter. I'm glad it's only $20. Ordered a new one... Still cheaper than everything else.

 

[Tubetec]

Opps ,

Its probably worth making a bold front panel label to remind yourself to discharge the cap before testing .

 

[rock soderstrom]

Then I was ready to test the caps I needed to test. I didn't discharge them and destroyed the meter.

Ouch, that's a pity . You are probably not the first to forget to discharge the capacitor under test. The TC1 even has a note in red on the front panel.

 

[Gold]

I know it says it. I'm an idiot. I was trying it out with new smallish caps from the bin. Then I went to test the 1400uF 100V cap and didn't discharge it. Oops.

 

[ruffrecords]

I know it says it. I'm an idiot. I was trying it out with new smallish caps from the bin. Then I went to test the 1400uF 100V cap and didn't discharge it. Oops.

You are only an idiot if you do not learn from your mistake.

Cheers

Ian

 

[Gold]

You are only an idiot if you do not learn from your mistake.

Cheers

Ian

I learned to have an extra one on hand for when I do it again.

 

[MicMaven]

You are only an idiot if you do not learn from your mistake.

Richards' Second Law:

There are two types of people in this world:​

those who learn from others' mistakes . . . and the others.​

​

James

 

[Tubetec]

The general advice about discharging caps is cro-bar the terminals with with an insulated screw driver,
This sends molten metal flying and subjects the cap to stress , resistor with croc clips is cumbersome if you have a large batch to test

A simple push button benchtop cap discharger would be nice , set up for the various spacings of electrolytic lead outs . Maybe a lightbulb in series with an NTC thermistor could work .

 

[Gold]

This is my hi tek cap discharger. It’s two 40 ohm 22W resistors in series with some old DMM leads.