Component Tester Uses and Review

Santa brought me two new tools this Christmas to help speed up faultfinding and diagnose issues with tech repair – a Neoteck Digital-Multimeter – that measures capacitance up to 100mF and a Dolla Tek T7 Multifunctional Tester also shows capacitance + ESR along with many other components.

Both were less that £20 from Amazon and are useful to diagnose component issues although they are not perfect and don’t test breakdown voltage on electrolytes — more on this later.

I’ve accumulated several cheap hand held multimeters over the years and my go-to instrument of choice for simple fault finding is the humble digital multimeter. With a somewhat limited count of 2000, all measure ac & dc voltage and current along with resistance. Two also measure NPN & PNP bipolar transistors, displaying their hFE gain together with diode voltage drops, both useful for identifying blown semiconductors. None, however, offer the Neoteck’s 9999 count range or Dolla Tek’s component variety.

But do these modern component testers, available at a similar price to a budget multimeter, deliver on that promise? Well, see what you think, based on my initial review findings.

First let’s compare their main features.

Functionality

Each meter provides a different set of functions with similar ranges for the resistance and capacitance. 

Capacitance measurement

Electrolytic capacitor replacement is arguably the most often cited repair suggested on DIY forums for failing tech gear and capacitor kits supply a growing market of customers.  With some basic soldering skills and patience it’s possible to replace all the electrolytic capacitors on circuit boards to rejuvenate poor sound and dodgy video on eighties games consoles or audio and video gear.

But do all the capacitors actually need replacing and is it worth the potential damage their removal entails? The answer is often NO. Some do indeed leak electrolyte damaging the copper circuit boards and adjacent components – the metal cased surface mounted types are the worst culprits. I’ve witnessed first hand the problems with Sony’s ICF-SW7600 radio and Sega Gamegear consoles to name but two.

Capacitance – The good

Once removed from a circuit board, Dolla Tek’s multifunctional tester makes it easy to check the capacity and effective series resistance and compare with a new stock electrolytic. The Neoteck lacks ESR measurement which may lead to incorrect diagnosis but both instruments have a range that extends up to 100,000μF or 100mF – well beyond the 20μF my old Gold multimeter manages.

Smaller capacitors are also handled with ease. The Dolla Tek’s DIP connector avoids residual lead capacitance that’s present using the Neoteck’s probe leads. Unfortunately the clip on leads supplied with the Dolla Tek, as used in the picture above, have a 0.11Ω resistance, so the ESR readings are all high by this amount. Also worth noting ESR & V loss is not displayed on values < 1μF

After testing a selection of NOS electrolytics I discovered a batch of 220μF 10v showed just over 120μF but kept changing value on the Neoteck. So I repeated the tests and found the Dolla Tek agreed the batch is indeed out of spec.

As I had kept a selection of suspect large value capacitors removed from previous restorations, I thought it would be interesting to see how many were in fact faulty along with a new 4700μF. Here’s what I found.

Capacitor test results

It’s interesting to note the majority of these old electrolytics read a higher value than specified. The Neoteck shows one at 1800μF above the 5000μF marked on the can – that’s 36% out, but the Dolla Tek does not agree suggesting only 800μF higher. A high value is not necessarily bad and in fact for most smoothing or reservoir uses it’s better to be higher than lower. What matters more is the effective series resistance which generates heat when subjected to ripple currents that can flow in this type of circuit. Over heating can damage the electrolyte and shorten the capacitor’s life. The ESR readings are all fairly low, so again, no particular problem. The Vloss percentage at 3.5% is a little high on one.

Neoteck electrolytic capacitor test

But the leakage currents at the rated voltages can’t be measured on either meter and this is what can give a better clue of imminent failure. This can only be measured by increasing the voltage applied to their maximum rating and noting the current flow. 

Capacitance – The bad

In most cases you need to remove the capacitors or at least one leg to take a meaningful reading. In circuit, there are often other components connected in parallel that can cause incorrect measurement and misleading results. The Dolla Tek may suggest a different component altogether as it discovers semiconductor junctions instead of the intended capacitor.

This makes fault finding more time consuming as you will need to completely remove radial lead capacitors to isolate them. I guess this is often why they simply are replaced without bothering to identify a faulty component. At least with axial lead caps it’s easier to lift one leg and check. If you have the schematic to hand it’s easier to check if an in-circuit test is sensible and avoid disturbing the PCB.

Neoteck’s high readings for some old electrolytics compared with the Dolla Tek T7 is odd. It may indicate the capacitor is faulty as a new capacitor of similar value correspond.

Capacitance – The ugly

You must remember to discharge capacitors before attempting a test, to avoid damaging the instruments or give incorrect readings. To be fair the Dolla Tek has a warning printed however a better design could automate this procedure and avoid potential damage. At these price points I guess it’s difficult to argue for a robust design so you need to be mindful and avoid the cost of replacing the meter.

ESR depends on test frequency and that’s not displayed on the Dolla Tek. So ESR is only of use when comparing different capacitors. You must also allow for the clip on lead resistance as noted above. The Neoteck doesn’t even offer ESR although it can measure frequency separately.

Inductance measurement

Inductors, although less common than capacitors in component faults, are a problem. Switched mode power supplies, found in many mains powered consumer devices, contain transformer coils and small value inductors that can be confused with resistors. Here’a an example that looks similar to a 1k resistor but is in fact a 1mH ½w inductor.

This example replaced one that failed open circuit – fine wire contained within the encapsulation had burnt out causing the body to break in two. While an ohms check using a simple multimeter can help identify faulty inductors, having a way to confirm a component’s actual value is useful.

Inductance – The good

Dolla Tek displays the coil’s inductance easily and includes its DC series resistance. In this example it’s showing 40% high which is way above the 5% tolerance specified. But is it the meter or the component that’s wrong?

Inductance – The bad

While the T7 confirms the inductance, it fails to measure effective series resistance or coil quality. This may not be important at low frequencies and it does show the coil’s DC resistance.

Neoteck does not offer inductance measurement. I missed this thinking it would be included as it had frequency and capacitance ranges. There are other alternatives such as a Proser multimeter which includes inductance but is limited to a 6000 digit range instead of Neoteck’s 9999.

Inductance – The ugly

Nothing to see here!

Frequency measurement (Neoteck only)

Frequency – The good

With a 10Hz to 10MHz bandwidth the Neoteck covers all audio and mid shortwave frequencies.

Frequency – The bad

The user manual gives the sensitivity or minimum level needed at 1v RMS. When I connected an oscilloscope to monitor, the output from my signal generator, it seems to operate with only 0.8v peak to peak. Worryingly the manual says results are not reliable if the level exceeds 20v RMS.

Note when AC voltage is selected the true RMS readings are only specified from 40Hz to 1KHz. This makes it difficult to check the level for frequency measurement above 1KHz and means it’s voltage measurement is unsuitable for bass and treble audio frequencies.

Frequency – The ugly

The Neoteck needs AC coupling when using frequency measurement.

If you try connecting the leads directly to a circuit with a DC offset the meter fails to register any frequency. I used a 100nF in series with the +ve connection but the meter should really incorporate this when selecting the frequency input function.

I could cut an old probe lead, adding a capacitor in line and keep this for frequency measurement. But I’d need a warning label so I don’t try to use it on other settings like resistance and wonder why everything’s open circuit!

Not a good design from Neoteck.

Other functions

I won’t cover all the meter’s functions in detail as there are so many, so I’ve picked out some pros and cons.

The good

Semiconductor testing with the T7 is almost addictive. Okay I should get out more! The ability to select matched pairs from a set of jFETs for example makes it possible to replace components and retain the original designer intent. This is important for hifi stereo amplifiers or any amplifier with a differential stage needing matched pairs. The T7 measures more than hFE / gain and being able to match all the device parameters such as capacitance is invaluable for RF applications.

Dolla Tek Component Tester

It’s handy to have a sensitive thermometer for some fault conditions and the Neoteck includes a temperature probe that responds quickly. Testing dehumidifiers is one area the temperature probe is useful. That said, FLIR cameras are available at reasonable cost and have proved useful in identifying high temperature components to aid fault diagnosis.

The Neoteck comes with two sets of good quality leads – a set of probes with covers and plugs each end and a set with bulldog clips. You can mix and match so it’s easy to clip one on a ground point and use a probe to check voltages (observing safety procedures in live circuits of course).

The bad

Neoteck’s spec suggests it covers a temperature range from -20℃ to 1000℃. I’d be amazed if the probe survives at 1000℃.

Neoteck decided not to include bipolar semiconductor measurement and only tests a simple diode junction. Again, this limits the Neoteck’s role if you want to carry one meter for field repairs. 

The ugly

To be fair at this price, neither component tester has any really bad functions to note.

Summary

So what’s the verdict? I intend to use both meters for portable fault diagnosis at Repair Cafes or field service or in the workshop. Both offer more features than my general purpose multimeters but neither provide a single solution, so I’ll have to carry both for all use cases.

Neoteck

In practice the Neoteck is just annoying after a few minutes due to its incessant beeping and if it wasn’t a present I’d likely send it back. I guess the designers were more worried about the meter being left on with a backlight to drain the batteries than they were about a customer’s sanity! When I’m trying to analyse the readings and think, the last thing I need is a distracting beep-beep-bloody beep.

And while it’s possible to inhibit the equally annoying auto power off or APO, that decides it’s time to switch off just when you’ve made contact and looking at the display, I can’t disable the beep. I tried taping over the beeper holes in the Neoteck’s base but it made little difference, so I’ll have to try and open the case to see if I can quieten it.

On a positive note the back lit display is very easy to read in various light conditions and much better than my standard LCD multimeters that can be frustrating to see in low light, balanced inside a car bonnet, cabinet or chassis.

Neoteck Component Tester

Dolla Tek

Dolla Tek’s T7 is an amazing piece of technology for the price. I remember back at university writing a computer program to simulate a circuit using matrix algebra and lots of logic. It took a mainframe computer to crunch the numbers and plot results on a line printer! Okay this was a few years ago, but it makes me appreciate how far we have come with microprocessor hardware and software design. Yes, Dolla Tek is just a Chinese copy of a European design and I bet the designer receives no royalty or compensation for their efforts.

The T7 is powered by a Li-on battery charged via a USB connector. It too has auto power off a few seconds after completing a test, which I can’t see how to disable. Again battery consumption seems the main concern. You get used to the single operation power down as the Dolla Tek has a simple push button to run a test rather than a separate on/off switch.

One of the best features is the T7’s ability to automatically identify a semiconductor and its pin out. It avoids the need to look up the data sheet when you don’t have one to hand – such as being stuck in a remote field trying to fix a tractor’s electrics.

However, I found the Dolla Tek’s accuracy and repeatability for basic resistance and capacitance measurement not as good as the Neoteck. The flimsy clip-on leads don’t help – they self measure 0.11Ω compared to the Neoteck’s impressive 0.000Ω. I made a new set of leads with crocodile clips that measure 0.02Ω and give more consistency.

Dolla Tek Zero Ohms Check

Review Notes

Retro Radio do not receive income from the Amazon links above and are included for information purposes only.

The two manufactures chosen in this review were suggestions for Christmas presents and not fully researched or endorsed as the best options. Both meters appear to be white label products – no manufactures identification are shown or included in any instructions – the Dolla Tek was supplied without a manual.

Neither are intended for professional use and while they appear to display values to several decimal places, the accuracy across the ranges varies. For example the Neoteck spec shows ±(3.5%+20) for capacitance, whatever +20 actually means!

I recommend you check the meter’s calibration using known components or reference sources within the ranges you intend to measure.

Finally, do keep in mind the Dolla Tek’s limitations – just like ChatGPT, it may not always make sense.