FNIRSI DSO-TC3 Multifunction Meter

I was sent this interesting little device. Well, calling it a device might be a bit generous; for the most part, it’s probably more of a display gadget. But it all depends on what you need it for, and for some tasks—especially the kind beginners in amateur radio tend to have—it’s perfectly adequate.

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I’ll start with the packaging, and it gets five stars. I know at least two companies that pack things this well: Fnirsi and RuiDeng. Given the potential mishaps during shipping, this is good packaging.
Inside was a box with the device and an extra bag.


The bag contained an oscilloscope probe, a standard one rated for 100 MHz, which is far more than this device needs.
It also contained a useful little adapter, from MCX to standard BNC.

Note: the items in the bag are an optional extra. There are two package options on the product page, so choose carefully!



The box with the device looks neat; there’s really nothing to complain about.


There’s also an extra box inside, containing:
1. MCX probe leads with alligator clips
2. USB-A to USB-C charging cable
3. Three wires with spring-loaded hooks.


There was also a brochure and a user manual. The manual has been fully translated—not into Ukrainian, but at least into Russian. And it’s clearly not a Google Translate job; the translation is quite good.


And here we are at the subject of the review. It definitely gets a plus for its neat, uncluttered appearance: restrained yet attractive.


1. Three MCX connectors on the top edge: voltage measurement, generator output, and oscilloscope input.
2. A USB port on the bottom edge for connecting the charger.
3. A label on the bottom with the power requirements (5 V, 1 A) and the installed battery capacity (1500 mAh).
4. There’s also a kickstand on the bottom, so you can prop the device up at an angle. Handy.

If you look closely at the photo, you’ll notice there are no screws. They’re actually hidden under the front panel, but the case looks quite solid. The only thing missing is rubber feet; as it is, it slides around on the table.


The front panel has:
1. A large LCD screen
2. A ZIF socket for connecting components under test; the only thing really missing is a pad for SMD components.
3. A power button, which also serves as the exit button (essentially, it’s a Back button).
4. A button to confirm a selection and enter the menu.
5. Four buttons for up/down and left/right. The latter two have additional functions. For some reason, though, the Hold button doesn’t freeze the readings; it toggles an additional display mode. The Run button actually handles Hold.


There are four operating modes:
1. Component tester, essentially a transistor tester.
2. Oscilloscope
3. Signal generator
4. Additional measurements/calibration



The component tester—there's really nothing new here. Anyone who's ever used a regular transistor tester will get the hang of it in 5 seconds.
The battery voltage is also displayed here, although the device has a conventional charge indicator as well.
Specifications from the product page
Triodes：β is greater than 10 and less than 600
Diodes：Forward voltage drop <4.5V
Reglulated diode：0.01~32V
MOSFET：JFET，IGBT，MOSFET
SCRs：Turn-on voltage <5V, gate Pole trigger current <6mA
TRIAC：Turn-on voltage <5V, gate Pole trigger current <6mA
Capacitor：25pF~100mF
Resistor：0.01Ω~50MΩ
Inductor：10uH~1000mH
Battery：0.1~4.5V



Oscilloscope, specifications from the product page
Real-time sample rate：10MSa/s
Analog Bandwidth：500Khz
Input resistance：1MΩ
Coupling method：AC/DC
Test voltage range：400V
Vertical Sensitivity (x1)：10mV-10V
Horizontal time base range：1us-10s
Trigger mode：Auto / Normal / Single
Trigger type：Rising edge / Falling edge
Waveform Freeze：Yes
Automatic measurement：Yes

It's pretty basic, but a 10 mV minimum range would obviously be a problem on a professional instrument. For a simple device like this, though, it's perfectly fine—at least it's much better than the 50 mV on my DS-203.
The frequency range is also sufficient for working with relatively low-frequency signals, and is more than enough for audio.
Otherwise, it's pretty simple, as I said, and suitable for a beginner electronics hobbyist. The automatic functions also mean you don't have to keep pressing buttons.


Signal generator, with a range of 1 Hz to 100 kHz. It can generate sine, square, variable-duty-cycle square, triangle, and variable-slope triangle waveforms, so it's easy to generate a sawtooth. In all modes, the range is 1–100000 Hz in 1 Hz increments, with an output voltage of 0.1–3.3 V in 0.1 V increments.
There's also a separate DC output function, from 0.1 to 3.3 V in 0.1 V increments.


Additional functions:
1. Continuity tester with buzzer, the classic kind that also measures resistance.
2. Voltmeter up to 40 V
3. Dallas 18B20 temperature sensor test
4. DHT11 humidity sensor test
5. Decoding NEC infrared commands. Not much to it and not something many people need, but it's there.
6. Transistor tester calibration. The procedure is the usual one: first short all the probes, then leave them open. Nothing out of the ordinary.

The description lists these brief specifications:
Input voltage：0~40V
DS18B20：0-85℃
DHT11：0-60℃/5-95%
Infrared remote decoding：NEC protocol infrared cod

I think the sensor testing is probably the most useful feature here, though the continuity tester could come in handy too.


Settings, opened by holding down the Menu button
1. Show the logo on startup.
2. Select Chinese or English. For some reason, the toggle works in reverse: the menu is set to English, but the switch is off.
3. Buzzer volume. Useful—I immediately turned it down to 10%.
4. Screen brightness. Also useful; I immediately set it to 100% because I was taking photos with a flash.
5. Restore default settings
6. Model name and firmware version


I ran a few tests, starting with the component tester.
And right away, I hit a snag. First I tried a KT858 transistor, but one way of connecting it gave me a capacitor, and the other showed two diodes.
I tried some imported D363, and everything was fine: it identified the transistor and displayed its parameters.
Then I tried a domestic 1T308 and got two diodes; with a KT3102, I got two diodes again.
I was starting to think the device had something against Soviet transistors, but then I tried a 2T312 and it turned out that wasn't the case—the tester measured it correctly.
The KT961 was fine too, as were the BU5027, IRFZ46, and IRF840.
But I liked the zener diode test even more. I tried a KS175A and a KS527, and it showed 7.5 and 26.9 V, respectively—perfectly reasonable.


The diode array was also identified correctly.
Next, I tested some passive components:
Inductance: fine, but the lower ranges are clearly not its strong suit.
The 7850 and 5600 pF 0.5% capacitors read low, noticeably so.
The 820 and 100 µF electrolytic capacitors were basically fine. The first read high, but it's new; the second read low and is noticeably older.
The 6.8 kΩ 0.5% and 24 kΩ 0.25% resistors read high.

Yes, I later tried other combinations of contacts and calibrated it, but that didn't change much.


Let's test the oscilloscope.
I used a UTG932E signal generator for this. Along the way, I noticed an inconvenience: although the connector fits quite snugly, it can rotate. That would be fine if only the MCX itself rotated, which is normal, and you had to insert a BNC plug into it, which also rotates. Anyway, I recommend putting the adapter on first, then connecting it to the instrument.



Since the square wave is the most critical waveform, I tested that one, because it’s much harder to mess up a sine or triangle wave.
Results at 60 mV and frequencies of 1, 2, 5, 10, 20, 50, 100, 200, and 500 kHz. Basically, the instrument gave up at frequencies above 200 kHz, getting closer to 500 kHz. It’s rated for up to 500 kHz, so I’d say it’s working as expected, since even with a distorted waveform I could still see the correct voltage.

One thing I didn’t like: the screen displays signal parameters such as frequency, duty cycle, and so on. These readings are sometimes nonsense: the frequency jumps by +/- 30–50 Hz, or the duty cycle does, even though I’m sure the generator is outputting a stable signal.


At 1 MHz, the square wave turned completely into a sine wave, but more importantly, the amplitude measurement was also inaccurate. Still, nobody promised performance above 500 kHz.
The test was done in AC mode, i.e. with DC blocked. The input capacitor’s capacitance also affects the result, so I tested at 100, 200, and 500 Hz. The photo shows that the signal is clearly attenuated at 100 Hz, barely at all at 200 Hz, and not at all at 500 Hz. Keep this in mind when measuring low-frequency signals, or use DC mode.


Next, I tested the built-in generator. By the way, it also works in oscilloscope mode, at 1 kHz, which is handy for calibrating a probe. I connected the oscilloscope input to the generator output.


Sine wave at 2, 5, 10, 20, 500, and 100 kHz. There’s not much you can do to mess this up unless you really try. The only thing is that the output voltage was set to 3 V, but it clearly started to sag at the upper end of the range.


A closer look at the 100 kHz sine wave: there’s a small step, but it’s basically fine.


Square wave at 10, 20, 50, and 100 kHz, again at 3 V. It’s fine up to 20 kHz; above that, the edges start to droop.


1–4. Triangle wave in the same modes.
5, 6. The same triangle wave, but in a separate settings menu where you can choose the slope direction and amount. I think the screenshots show 20% and 80% slope, respectively. Set it to 0 and 100% and you get a sawtooth wave.


DC mode: I set it to 0.1, 0.2, 0.5, 1, 2, and 3 V. 0.5 V and above are quite acceptable; below that, not so much. Of course, this is all rather subjective, since it isn’t marketed as a calibrator.


Voltage measurement: I applied fixed voltages of 10, 20, 50, 100, 200, and 500 mV, and 1, 2, 5, 10, 20, and 40 V from a power supply.
Below 5 V, the measurement error is fairly high. It read 5, 10, and 20 V perfectly, and under-read 40 V.


But in the process, I actually discovered an oddity.
1, 2. I set it to 10.007 V, so the tester should have shown about the same, but it displayed 10.000–10.001.
3, 4. I increased it by just 1 mV, setting it to 10.008, and it started showing 10.004–10.009.
Of course, you could say the power supply itself is partly to blame, but no: its output voltage is 1 mV below the set value. But when I increased it in 1 mV steps, my UT181A also showed an increase of exactly 1 mV: 10.001, 10.002, 10.003, and so on.

So the last digit is bogus.


Continuity test. I really liked it: not as scratchy-sounding as the M890, but still really fast and crisp. Five stars.


What’s inside?
I first tried to take it apart myself, but it wouldn’t budge. I went online to see how it comes apart and found a page with a review and teardown. I changed my mind about taking it apart, since there was no point anymore.
Anyway, there’s a decent little review, supposedly in Korean, but the pictures are what matter: link

It also shows how to take it apart. I think the previous version had screws at the bottom of the case. Maybe the author had no trouble taking it apart because his unit opened up in the same color as the device. Mine is orange, so that didn't work :)



Inside, there's a single circuit board and a battery rated at 1500 mAh in the product description.


A closer look at the board: a processor with its markings rubbed off, a bunch of discrete components, a relay, and so on.


On the underside are the buttons, the photodetector, and the socket.


The author also pointed out the messy soldering on the photodetector and connectors. I completely agree: it looks bad and it's not right.



Conclusions.
I'll say right away that calling this a measuring instrument isn't really accurate. It's more of a gadget that gives you readings, but it's quite functional and convenient all the same. It'll be handy for a beginner, mostly because of the component tester. If they get into building amplifiers, the oscilloscope and signal generator will come in useful too.
I'm not going to be too hard on it. It is assembled neatly, at least on the outside, and its accuracy is reasonably good. The oscilloscope works fine up to 400–500 kHz. For power supplies, that's only really enough to check ripple, but it's fine for various audio projects. The signal generator is useful too and works well. The voltmeter is so-so, but the continuity tester is great.
Speaking of the continuity tester, I checked the voltmeter first, then switched to continuity mode and spent ages trying to figure out why it wasn't working. It turned out you have to plug the probes into the socket for continuity testing, not the MCX connector. Honestly, that's inconvenient. They could have put this function on the same connector, especially since continuity testing and the voltmeter are next to each other in the menu.

My short version: if you have a young electronics hobbyist in your family or among your friends, and you don't know what to get them, I definitely recommend this. They'll like it.

The store provided a discount coupon: TC8888, $5 off, valid from 13.01.2024 00:00:00 to 20.01.2024 23:59:59



That's all for today. I hope you found this useful, and as always, many thanks for your support and comments.