$20 LCR ESR Transistor checker project

[indman]

Try to play with that 5 ohm resistor instead of 5,1k. It seems that 5 ohm resistor is a shunt in current supply unit (similar to power supply for led). Put variable resistor in place of 5 ohm and try to change current using it.

MaxFrister If now you have nothing warmed up and check stabilitrons works fine, then do not touch anything else and listen to other silly advice, otherwise you risk to lose serviceable device! 

[vklimk]

Try to play with that 5 ohm resistor instead of 5,1k. It seems that 5 ohm resistor is a shunt in current supply unit (similar to power supply for led). Put variable resistor in place of 5 ohm and try to change current using it.

silly advice

Actually the advice can be not so silly.
Look. It is typical application of SDB628 in image1, it is voltage source:

But SDB628 can be used as a current source, see image2:

A current through D2 will be equal to 0.6/R2 (in case D2 rating is bigger than Vin).
If R2=5 Ohm, then the current will be 120mA.
If R2=40 Ohm, then the current will be 15mA.
Look at the image you posted more carefully and you will see that it is the case. So, there will be no 0,7A current there, just 15mA.

[indman]

If R2=5 Ohm, then the current will be 120mA.
If R2=40 Ohm, then the current will be 15mA.

I don't need to explain the theory of how a simple chip DC-DC works.I can give you a big lecture about her work myself. The current of 15mA, and even more 120mA, which you have "calculated" is many times higher than the maximum permissible for checking a low-current zener diode. I repeat once again - do not give silly advice if you are 100% unaware of the complete connection scheme of the zener diode from Chinese "engineers".

[vklimk]

Whole circuit is clearly visible in the photo you provided. You can see that it is the same as I provided in image2.
I believe that you have a big background in electronics, much bigger than mine.
But please don't be so aggressive, be more polite.

[Feliciano]

Let me try to shed some light on the subject:
1.- Let's say the "designer" of this clone took the typical schematic from the boost converter datasheet, and forgot to add a current limitation (by mistake, or to save a few more cents)
2.- Let's say the boost can source 100mA and 30V (just a guess, I don't have measurements of the circuit with its chinese ICs):
2.1.- If you try to test a 30V zener, you are applying 3W to it (P=V*I). If it's an small zener (0.25W or 0.5W) you will fry it, or if supports it for short term, you would be testing it outside its intended operating window
2.2.- On the other hand, if the efficiency of the boost converter is around 85%, you will be asking close to 1A from the battery. For a small Li-ION battery, you will be exceeding the recommended C-rate
2.3.- If you put a small resistor in parallel to the zener, you will be lowering the maximum zener voltage you can measure, and for small-V zener (like 3.3V), you will still applying a lot of current to it, and drawing high current from the battery, whether you're testing a zener or not
2.4.- If you modify the IC voltage divider, you will be still lowering the open circuit output voltage, but not limiting the current
Therefore, as madires suggested, the best mod for a circuit like this it would be to add a current limiter, or if space is a problem, at least a series resistor, as indman suggester earlier (just make sure to add it before the measuring loop)

[indman]

A competent and simple solution, as indicated in the screenshot. Selection of the most optimal current and its stabilization for safe testing of high-power and middle(low)power zener diodes.

[MaxFrister]

I'm not quite sure how you installed the extra resistor? Can you show a high quality photo of this section of your PCB with the resistor installed?

Attached is a picture of my ugly fix as well as an attempt at reverse engineering of the LCR-T7 zener test circuit.

It looks to me like the resistor R16 is bad and that it is intended to control the feedback pin of U7 in constant current mode (0.6V/60R = 10mA).   

[indman]

On my unit, "A" is connect to ground via a 5-ohm resistor.  I'm not really sure why. 

Why do you think that R16 on your board has a resistance of 5 ohm? The internationally coded 59X stands for 40.20 ohms ± 1%.
Your board has exactly the same resistor rating as the one I showed in my example.

[MaxFrister]

Why do you think that R16 on your board has a resistance of 5 ohm?

That is approximately what it measures in circuit.  I can pull it and measure it accurately tonight.

Does anyone know what IC U7 is?  It is not the SDB628 mentioned above; the pin wiring does not match.

[indman]

That is approximately what it measure in circuit.  I can pull it an measure it accurately tonight.
Does anyone know what IC U7 is?  It is not the SDB628 mentioned above; the pin wiring does not match.

U7 is very similar to SY7208CABC in the location of the contacts, but this cannot be said with 100% certainty, because the HYDSI or HYDWE marking does not appear anywhere yet.

P.S Here is an even more likely interpretation of U7 - this is AN_SY7200A (marking HY6VE). If you believe the documentation for this chip, then the output current is calculated by the formula I=0.2/R1. If R1 = 40 ohms, then the test current I=0.2/40=0.005A, that is, 5mA.

Now it remains to solve the riddle from Chinese friends -why does this circuit not withstand a given R1 current and allows it to conduct a much higher current?

[vklimk]

Because of open circuit. There is no load to inductance if you do not measure zener diode and there is no current, there is no voltage drop at current sensor resistivity and IC tries to add more and more power, it works at its maximum, it loads a lot of power into inductance and inductance generates high voltage pulses. And these high voltage pulses from inductance go to both capacity and IC itself. Both of them get fried in some time. If there is a big current then it means that feedback part of IC has already been fried and resistance between pins 2 and 3 is very small (shorted), such fried IC continues to work but with no ability to adjust the current by mean of that 40 ohm resistor any more.

[indman]

It is possible, although according to the documentation, this chip should have good overload protection for mode of open circuit.
And here is also an important note from the datasheet, which should be taken carefully:
"6) If the system chip interfacing with the EN pin has a
high impedance state at shutdown mode and the IN pin
is connected directly to a power source such as a Li-Ion
battery, it is desirable to add a pull down 1Mohm
resistor between the EN and GND pins to prevent the
noise from falsely turning on the regulator at shutdown
mode."

[vklimk]

Low quality of these ICs I think...
We know that it can be not easy task to purchase good quality electronics parts from China. Maybe fnirsi have purchased defective ICs for their devices.

[indman]

Low quality of these ICs I think...

On this most likely assumption, I certainly agree with you. Probably a fake of chips, which is similar to the same fake of microcontrollers.

[MaxFrister]

Why do you think that R16 on your board has a resistance of 5 ohm? The internationally coded 59X stands for 40.20 ohms ± 1%.

I ran some measurements on my board.  First I returned it to it's original configuration and measured the current.  Testing a 2V zener, it uses 52mA.

I removed R16 and measured it out of circuit.  It measures 40 ohms as you expected.  I returned it to the circuit and it measures ~7 ohms. 

I think it is likely that U7 is bad. 

Does zener testing work on any LCR-T7 boards?

[indman]

I returned it to the circuit and it measures ~7 ohms. I think it is likely that U7 is bad. 

Yes, you have a faulty U7! 7 ohms is the resistance between 2 and 3 pins of U7!
If you find an original high-quality SY7200A and install, then testing zener diodes will work fine on your clone.Also, according to the documentation in the circuit, it is desirable to install an X7R type capacitor at least 2.2 mkF(low ESR) at the output voltage, as well as to ensure a minimum load on the chip in the form of a resistor (pick up the nominal value), which will exclude possible self-excitation of the circuit in idle mode(open circuit).

[Yuriy_K]

It was possible to obtain acceptable measurement results of the TTester using the Mega2560. Additionally, I installed capacitors and replaced the capacitor with AREF. Scheme and examples of measurements in the pictures.

[madires]

The ATmega2560 also has sufficient pins for driving larger displays (ILI9481, ILI9486 or ILI9488) via 8-bit parallel bus.

[ozkarah]

I have a new BSIDE ESR02 Pro. I want to check which firmware it came with but no FW version is published either on the boot screen, or in menu options.
Does anyone know how to learn which fw it has and which version?

[madires]

IIRC, they come with a modified older k-firmware. You can update the firmware to the latest k or m-firmware if you like.

[Martini]

I'd like to buy my first (and hopefully last) component tester. Could you advise me the right hardware and firmware depending on my requirements?

[snapper]

hello,
does anyone here know this version with socketed µC and may know a source of purchase ?
regards

[madires]

I'd like to buy my first (and hopefully last) component tester. Could you advise me the right hardware and firmware depending on my requirements?

Please see https://github.com/madires/Transistortester-Warehouse/blob/master/Documentation/English/Clone-Comparison-Chart.pdf for an overview.

[madires]

does anyone here know this version with socketed µC and may know a source of purchase ?

Looks like an LCR-T7 with ATmega328. You can get them from most shopping platforms. However, finding the exact same one could need some effort as there are several different LCR-T7 models.

[wandows]

Hello everybody!
After updating the firmware I'm having some problems, could any friends help me solve this problem (M328_KIT_TFT)?

Firmware version 1.47m

config.h
#define HW_ENCODER
#define ENCODER_PULSES   4
#define ENCODER_STEPS    20
#define HW_REF25

Note: The device works normally with the original firmware


Thanks!