$20 LCR ESR Transistor checker project

[Feliciano]

Do y'all think it is likely to be problematic for my tester to always try applying a reverse bias of around 30V with 5mA current limit whenever it sees a diode junction? Is that likely to burn out random components?

I guess you're talking about to trigger the 30V generation at the end of all the other tests, provided it really looks it's a PN junction?
However, IMHO to apply 30V to a DUT can be arguably risky. Let's say you have a tiny low-voltage component (we could even say it's a 3-leg smd with dirt/loose contact on one), you could damage it. If you're doing your own CTester, I would rather assign a different set of terminals for that (like the TC-1 and its variants). This is just my opinion, for sure other people can shed more light on this.

[madires]

I agree. For example, some LED types don't like high reverse voltages.

[NF6X]

Ok, thank you both. The automatic Zener test idea is out. I would still like to have a single transistor test socket for the device under test, so I'll provide some way for the user to configure the unit's test mode.

[Dumidan]

Hello!

A test of a reverse-biased pn junction would be useful to establish the maximum reverse voltage, but for the test to be non-destructive, the current must be limited to a very small value, on the order of 0.1 mA or less. The test can be done on the section reserved for measuring zenner diodes, using a special current limiting stage. In no case can it be implemented as an automatic function due to special hardware requirements.

[NF6X]

Adding a low-current reverse breakdown test would push the tester's capabilities a tiny bit closer to a curve tracer. That has me wondering what a low-cost curve tracer inspired by the cheap LCR tester project might look like.

[morgan_flint]

Not exactly inspired by the cheap LCR tester project, but as simple as it can be:

https://www.instructables.com/Transistor-Curve-Tracer/

EDIT: Yes, it's inspired by this project: "I was very impressed when I bought one of the wonderful LCR-T4 testers by Markus Frejek and others but I wanted it to tell me more about the components so I started to design my own tester."

[pizzigri]

Not exactly inspired by the cheap LCR tester project, but as simple as it can be:

https://www.instructables.com/Transistor-Curve-Tracer/

EDIT: Yes, it's inspired by this project: "I was very impressed when I bought one of the wonderful LCR-T4 testers by Markus Frejek and others but I wanted it to tell me more about the components so I started to design my own tester."

Hi ! Did you build it? I tried some time ago (actually two years ago) using the smd version but it never worked correctly, possibly my fault….

[morgan_flint]

No, I haven't built it.

BTW, I think it'd be interesting a screenless version, just sending commands and seeing the results from a PC

[Pilot Error]

Hello everyone, I'm a bit new to this so I've now got a collection of testers with unmarked chips. I was interested when I read the information about this LCR-TC3 as it said using 'imported chips'.
Anyway there is a Atmel 328p in this so what does everyone think?
I've checked the pins and it's genuine as far as I can tell. Also it has two 180mah batteries. This was from an AliExpress seller 

[Feliciano]

Welcome to the forum.

Here a post relevant to the subject by our guru madires:

Some hints on identifying the MCU:
- MCU in DIP is usually an genuine ATmega.
- APT32F172K8T6 has different power pins:
  - 32-LQFP/QFN: 18=Vss, 19=Vdd (ATmega328 32-TQFP: 5=Gnd, 4=Vcc)
- APT32F172K8T6 uses SWD port for ISP:
  - 5 pins: Vdd, Vcc, F_SDAT, F_SCLK, F_RST
- Testers with APT32F172K8T6 often lack a quartz crystal.
- LGT8F328 has slightly different pins:
  - QFP32L: 21=PE2/SWD (ATmega328 32-TQFP: 21=Gnd)
- LGT8F328 uses SWD port for ISP:
  - 5 pins: Gnd, Vcc, SWD, SWC, Reset
- Clone variants with an genuine ATmega are usually about EUR/US$ 5 more
  expensive than the variant with a different MCU.

[Pilot Error]

Welcome to the forum.

Here a post relevant to the subject by our guru madires:

Some hints on identifying the MCU:
- MCU in DIP is usually an genuine ATmega.
- APT32F172K8T6 has different power pins:
  - 32-LQFP/QFN: 18=Vss, 19=Vdd (ATmega328 32-TQFP: 5=Gnd, 4=Vcc)
- APT32F172K8T6 uses SWD port for ISP:
  - 5 pins: Vdd, Vcc, F_SDAT, F_SCLK, F_RST
- Testers with APT32F172K8T6 often lack a quartz crystal.
- LGT8F328 has slightly different pins:
  - QFP32L: 21=PE2/SWD (ATmega328 32-TQFP: 21=Gnd)
- LGT8F328 uses SWD port for ISP:
  - 5 pins: Gnd, Vcc, SWD, SWC, Reset
- Clone variants with an genuine ATmega are usually about EUR/US$ 5 more
  expensive than the variant with a different MCU.

Thank you for the welcome message and this useful information. After checking the grounds and vcc it seems this tester does have a genuine Atmel chip. I shall explore it's functionality

[Feliciano]

Continuing with the TC1, I have one FNIRSI 324p-based (with power MCU as U8, transformerless, still with its factory firmware). It has a failure: Most of the times doesn't work, but sometimes work. I found the failure after I rubbed away the ugly whitened factory solders with alcohol. I had it on a drawer until recently.

Given the fact is not easy to find an ATmega unit, I'm trying to troubleshoot it. I describe its weird behaviour:
.-Most of the times get stucked with only "M-TESTER" message on screen. U6 (boost converter) generates 6.1V and the 78L05 4.9V. I can power it off by long-pressing the button
.-If it pass the boot banner, sometimes shows wrong (lower) battery voltage, and measures a phantom uF-range capacitor, sometimes between terminals 1 and 2, sometimes between 2 and 3
.-I already cleaned everything with alcohol or contact cleaner several times, and redo the solderings. While doing this, I found if I moisturize U6 with little bit of alcohol, it works for some minutes, with U6 delivering 5.9V
.-Sometimes works fine on its own

[EDIT]: Desoldering U6 and cleaning beneath it didn't solve the issue.
[EDIT]: I haven't found an Schematic of the transformerless variant to better study U6 behaviour here, In the meantime, I'm looking at the SB6284 datasheet.

Has somebody found/fixed an odd failure like this?

[madires]

-If it pass the boot banner, sometimes shows wrong (lower) battery voltage, and measures a phantom uF-range capacitor, sometimes between terminals 1 and 2, sometimes between 2 and 3

That points to a power supply issue. Could be something like a nearly shorted MLCC around the boost converters or the 78L05.

[Feliciano]

I think the failure is located around the boost converter (lC marking B628), because if I somehow alter a little its Q point, it works. In fact I re-centered the output capacitor, and cleaned beneath U6 and some resilient goo around L1 and it has been working for a few hours. Fingers crossed.

[madires]

Heating up the MLCC could have fixed the issue.

[Feliciano]

It could be, because this time I heated it a lot (and even rolled it over). I keep watching it.

Anyways, I was about to ask you:

a nearly shorted MLCC.

IIUC, you're describing that some layers can be shorted or compromised? If that's the case, it should measure a lower capacity and/or high ESR, and/or high Ileak and/or high Vloss, right?. I didn't notice some really bad values of it (from k-firmware), but without knowing the nominal value for my transformerless variant, I'm not sure. Still, how come when it had some vapour/liquid residues nearby it worked?

[madires]

MLCCs can fail in different ways. One is a dead short, and another is a low resistance (a few or 10s of Ohms). And there's also some humidity issue which can sometimes be resolved by simply heating up the cap. I have no idea why the alcohol helped temporarily.

[YouCanDoIt]

Hello to all guys,
I just joined the forum after spending a good amount of time in researches without coming up to a solution.
From what I have understood, as of now a device with an ATMega644/ATMega1284 and higher is the most desiderable because allows higher accuracy and many more features.
Hovewer, in the clone comparison chart I only see Hiland M644 which is limited to ATMega644. Very hard to find and sold at $40 in a couple of places. Some web pages before this one, an user said that it is just a waste of money which makes me think there would not be any significant difference between the old versions.
The list also shows some "LCR-T** marked as "possible ATMega644". I suppose the situation would be even worse for such models.

What seems to be very amazing is the Mega-4GSL, but I have not been able to find any DIY kit anywhere. Did someone here in the forum tried to build one? Where to find all the needed parts? I have no idea on the costs, but if there are other interested users we could create a purchase group and help each other in the build process.

Apart from this, are there any other alternatives?

[Feliciano]

Welcome to the forum.

Currently it's not easy to find an original ATmega unit (I guess politics and economics reasons). Therefore you can buy any and use it with it's original Chinese firmware (keep in mind the fancier the interface, the less functionality). Or you can keep looking for an original one, being able to flash the OSHW firmware discussed on this long thread, where you can select a set of the most important functions to your liking. Note: If you buy a DIP version, you have better chance of getting a real 328.

Or as you said, you can build one yourself (with an 644 or 1284, for reacher fetures set), alone, or along with some other European readers.

[jdev99]

Just received this one, with original ATmega328P. They are still out there. 

https://www.aliexpress.com/item/1005005497252414.html?spm=a2g0o.order_list.order_list_main.5.52321802KA7hcS

[YouCanDoIt]

Currently it's not easy to find an original ATmega unit (I guess political and economic reasons). Therefore you can buy any and use it with it's original Chinese firmware (keep in mind the fancier the interface, the less functionality). Or you can keep looking for an original one, being able to flash the OSHW firmware discussed on this long thread, where you can select a set of the most important functions to your liking. Note: If you buy a DIP version, you have better chance of getting a real 328.

Many thanks for your help. I was originally planning to buy "M328Kit+TFT(AY-AT)" I saw on the chart since this one seemed to be the best one. Is right? Please accept my apologies for the stupid questions, but I am totally newbie about transistor testers. This model seems to be non DIP and therefore should be easier to find a genuine version, but what is the difference between DIP and non DIP versions?
There is still the problem that an ATMega328 can't run a full feature firmware and its low accuracy. Given the low price of the controller, I am wondering if I could just replace the bundled ATMega328 with an ATMega1284 and flash it with the related firmware.

Or as you said, you can build one yourself (with an 644 or 1284), alone, or along with some other readers.

Yes, this is the option that I'm currently evaluating, but it's getting harder than I thought due to the lack of sources. I thought to the Mega 4gsl because it has been mentioned here, but I should first try to understand how it really performs to see if it's worth all the efforts to build one.

I'm also unable to estimate costs. There are 150 components. By a quick (and dirty) look up it should be around 15-20$ for the board components, $5-15 for LCD+battery (depending from what can be adapted). It should remain the PCB and the case, but I have not been able to find these anywhere. The user pizzigri posted here what he spent to build one and I got totally shocked to see it was 140 € (euro). Hope it has been a typo.

If someone can post some documentation source I would really appreciate. The PCB photo shows a non existent link to https://www.mikrocontroller.net/svnbrowser/transistortester/ and I'm wondering if this is a dead project. The firmware is heavily customized and I have read somewhere it is private. I am concerned about updates given the fact that the official ones regularly published will not work for sure.

Just received this one, with original ATmega328P. They are still out there...

Many thanks for the link. It seems to be a version of the GM328A different from the ones showed in the comparison chart. Isn't "M328Kit+TFT(AY-AT)" a better choice?

[YouCanDoIt]

I forgot to mention that I have also considered smart tweezers given the fact that now prices are more accessible. For example I saw here in the forum DT71 and although I have read many good reviews on the web, the one posted here is not good at all:
https://www.eevblog.com/forum/blog/eevblog-1335-miniware-$70-dt71-lcr-tweezer-review
That topic was around 3 years ago, so may be they managed to improve the quality through firmware and/or hardware changes.
I suppose that in the meanwhile new models entered in the market, but I'm not an expert and I have not gone further.

What I would like to know is that, for such price range, smart tweezers could be a better replacement of any of the best testers discussed on this topic.

[Feliciano]

If you buy a DIP version, you have better chance of getting a real 328.

but what is the difference between DIP and non DIP versions?

(Besides one being rectangular and larger whereas the other square and smaller), as we have been discussing on this thread, it seems the knock-off MCUs are being manufactured on small square encapsulations (cheaper), so that's why some of us think if you look for a DIP28 ATmega328P-PU, and if the vendor photo it's accurate, you have chances of obtaining a read one (with 32KB of flash, of course).

There is still the problem that an ATMega328 can't run a full feature firmware and its low accuracy. Given the low price of the controller, I am wondering if I could just replace the bundled ATMega328 with an ATMega1284 and flash it with the related firmware.

If you have a real ATmega, you can evaluate what changes you could make. Or, if you have an LGT8F328P-based unit, and you have a real ATmega, you could adjust the pinout and make the replacement.

If someone can post some documentation source I would really appreciate. The PCB photo shows a non existent link to https://www.mikrocontroller.net/svnbrowser/transistortester/ and I'm wondering if this is a dead project. The firmware is heavily customized and I have read somewhere it is private. I am concerned about updates given the fact that the official ones regularly published will not work for sure.

kubi48, madires, and indman have posted documentation on different sites. madires has gathered many of that  (including an overview I composed) at github.

[rfink07]

Hi, first time posting here. Let me know if there is a better place to ask this.

I bought a variant of this product recently, mostly to measure transistor gain. I've measured several 2n3094 and 2n3096 components, and they all measure hFE ~ 370. If I'm reading the datasheets right, it shouldn't exceed 300 (and usually be much lower).
https://www.amazon.com/Mega328-Digital-Transistor-Resistance-Capacitance/dp/B07WT9VVZB#customerReviews

Am I missing something? I saw that there can be measurement errors for leaky parts (germanium), but haven't seen complaints about common Si parts.

[rsjsouza]

Assuming the transistors are legit, historically the hfe alone is a parameter that has a wide variability across manufacturers and even within the same manufacturer or the same batch. Also, it is highly dependent on the bias applied to the transistor.

I wouldn't rely much on it, unless you are talking variations of orders of magnitude...