$20 LCR ESR Transistor checker project

[RoGeorge]

Maybe make that an option, not the default.

Such a warning will become annoying from day one.  Will also defeat the whole idea of this instrument.  This instrument stands out exactly because it needs zero training.  Connect something and whatever you throw at it, the instrument does the rest.

[dazz]

I vote for slapping the entire README in a "welcome" screen and force the user to scroll down the whole thing before getting a reading. 

[indman]

Maybe make that an option, not the default.

Don't take my post above too seriously. Pay attention to the emoticons.

[elecdonia]

elecdonia,I think you may back edit your post regarding ATmega324 and its support in k-firmware.

I am very eager to get LCR-TC2 containing either ATmega324 or ATmega644. So far I received one unit with LGT8F328P and another with APT32F172K8T6. So a week ago I ordered a third unit described by vendor as LCR-TC2.

Great news: I received the LCR-TC2 today. It contains ATmega324. I don’t have photos to post yet, but I did confirm the PC board looks exactly like the PC board in this post:
     https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4639780/#msg4639780

My plan is to replace the ATmega324 with ATmega644. However I think I will try out the -k and -m firmware for ATmega324 first, before upgrading the MCU.

[vever001]

Hi everyone,

I have a TC-1 model. Everytime I want to use my tester the battery is flat 
I'll probably make the recommended TC-1 mod from https://github.com/madires/Transistortester-Warehouse/blob/master/Hardware/TC1-Mod.kicad.tgz to prevent the battery getting drained.
But I would also like to change the tiny litium cell in it for 1 or 2 standard 18650 cells.
I will also probably design and 3D print a suitable case for it.

Now I see the lithium cell has a BMS.
If I go with a single 18650, can I reuse the existing BMS?
Can I safely wire two 18650 cells in parallel each having their own BMS?
If so what kind of BMS should I choose?
Do I really have to use BMSes in the first place or is it just for safety?

Thank you

[elecdonia]

Hi everyone, I have a TC-1 model. Everytime I want to use my tester the battery is flat 

There may be something in the hardware which stays on all the time even when display is off.

Please measure the current flow from the battery to the PC board for both the operating state (display on) and the sleep state (after display turns off) and post the results.

Also please post photos of the PC board.
Several different manufacturers are now producing LCR-TCx units. So far I have identified 3 totally different circuit designs:
   1) LCR-TC1 with APT32F172K8T6 MCU, 32-pin TQFP square package. This is same size package as ATmega328. But totally different pinout.
   2) LCR-TC1 with LGT8F328P MCU. Also 32-pin TQFP. Pinout is different than ATmega328, also different than APT32F172K8T6.
   3) LCR-TC2 with ATmega324 MCU, 44-pin TQFP package. I think older LCR-TC1 units (2021 and before) also contained ATmega324 MCU.

So far all of my LCR-TC1 (or -TC2) units hold a battery charge for several weeks or more. I will endeavor to measure their battery currents and post the results.

[vever001]

Wasn't the issue already identified by those who created the TC1-mod? Which is supposed to fix this exact issue I believe.
Right now I'm running the alternative firmware for the U4 chip https://github.com/atar-axis/tc1-u4

I have the version with ATmega324PA, so circuit design n°3 that you described.
I'll measure the current draw when I have some time.

[RoGeorge]

Everytime I want to use my tester the battery is flat

Mine has the same 9V alkaline battery since 2015.  The instrument is used rather rare, but the battery was connected all this time.  Battery is less than half now.  There is no mechanical switch.  The instrument goes to standby by itself, at a few seconds after each measurement. 

[masterdums]

Hello. Can you share the project in Proteus?

[Feliciano]

Hi everyone, I have a TC-1 model. Everytime I want to use my tester the battery is flat 

There may be something in the hardware which stays on all the time even when display is off.

If we're talking about an unmodified old version of the TC-1, that's a known issue. If you dig into the messages of june 2018 of this thread, you will find recommendations for replacing the U3 (or U4) that draws some idle current (with the screen off), replace it with a new power management circuit, and flash the m-firmware (don't forget to set the fuses too).

Or if you have one of the new non-Atmega versions, maybe you need to check the battery itself (and the new shipped batteries are tiny).

I think older LCR-TC1 units (2021 and before) also contained ATmega324 MCU.

Also the old versions of the T7. For more details, you can consult the Table of Clones.

[vever001]

Indeed, this was my understanding.
I plan to replace U4 with the TC-1 mod but I would also like to use 18650 batteries since the current battery is tiny.

My main questions was about the BMS and possibly wiring 2 18650 in parallel.

[indman]

My main questions was about the BMS and possibly wiring 2 18650 in parallel.

Why attach an 18650 and a BMS module if you can use a 2600mAh battery and forget about the power supply problem?
This battery fits perfectly in the TC-1 case.

[py-bb]

So I had one of these (a T7) but it just broke and now thinks everything's a zener diode. Any idea where one can get a "good" one - I love the feature set and speed - it was a great tool but yeah I'm annoyed now. Would appreciate any advice.

[Feliciano]

If the one you have has a protection IC, try removing it. Else, it looks you will have to find a replacement unit. The "good ones" are "old stock", so try thinking where to find that for your country.

[elecdonia]

So I had one of these (a T7) but it just broke and now thinks everything's a zener diode. Any idea where one can get a "good" one - I love the feature set and speed - it was a great tool but yeah I'm annoyed now. Would appreciate any advice.

Try this: Connect DC voltmeter to “A” and “K” zener test ports. Minus to “A,” plus to “K.” Then press LCR-T7 “START” button and observe voltmeter. It should read >25V. If <24V then there is a fault in the DC-DC converter circuit which steps up from the battery voltage to the expected 25-30V zener test voltage.

I believe the software checks this “A” to “K” voltage first. If >25V then it concludes “no zener is connected” and moves on to performing the standard transistor tester tests at ports 1,2,3. But if open-circuit voltage from “A” to “K” is <24V then it stays in zener test mode and won’t do anything else.

Also please test several zener diodes, for example 5V, 12V, 15V zeners. Are the results within +/- 1V of the zener’s rated voltage? Also while testing a zener diode: Does the zener get hot after few seconds? (It shouldn’t). If zener gets hot there is definitely a fault in the zener test hardware circuit.

I have three different LCR-x transistor testers with totally different internal circuit designs. Starting in 2022 some Chinese manufacturers substituted <$1 USD MCU chips for the traditional Atmel ATmega328, -324, or -644 MCU ( >$5 USD each and rising ). One of my LCR units with non-Atmel MCU developed the “zener gets hot” fault but otherwise still works OK otherwise.

My units have the following open-circuit voltages from K to A:
LCR-TC2 with  Atmel ATmega324 MCU:   25.4V
LCR-TC1         APT32F172K8T6 MCU:      30.2V
LCR-TC2         LGT8F328P MCU:             25.2V

Note: The Chinese manufacturers interchangeably label their models as LCR-T7, LCR-TC1, or LCR-TC2.The only way to identify “what is inside the plastic box” is from a photo of the PC board. However the vendors don’t provide photos of the PC boards. 

[py-bb]

So I had one of these (a T7) but it just broke and now thinks everything's a zener diode. Any idea where one can get a "good" one - I love the feature set and speed - it was a great tool but yeah I'm annoyed now. Would appreciate any advice.

Try this: Connect DC voltmeter to “A” and “K” zener test ports. Minus to “A,” plus to “K.” Then press LCR-T7 “START” button and observe voltmeter. It should read >25V. If <24V then there is a fault in the DC-DC converter circuit which steps up from the battery voltage to the expected 25-30V zener test voltage.

I believe the software checks this “A” to “K” voltage first. If >25V then it concludes “no zener is connected” and moves on to performing the standard transistor tester tests at ports 1,2,3. But if open-circuit voltage from “A” to “K” is <24V then it stays in zener test mode and won’t do anything else.

Also please test several zener diodes, for example 5V, 12V, 15V zeners. Are the results within +/- 1V of the zener’s rated voltage? Also while testing a zener diode: Does the zener get hot after few seconds? (It shouldn’t). If zener gets hot there is definitely a fault in the zener test hardware circuit.

I have three different LCR-x transistor testers with totally different internal circuit designs. Starting in 2022 some Chinese manufacturers substituted <$1 USD MCU chips for the traditional Atmel ATmega328, -324, or -644 MCU ( >$5 USD each and rising ). One of my LCR units with non-Atmel MCU developed the “zener gets hot” fault but otherwise still works OK otherwise.

My units have the following open-circuit voltages from K to A:
LCR-TC2 with  Atmel ATmega324 MCU:   25.4V
LCR-TC1         APT32F172K8T6 MCU:      30.2V
LCR-TC2         LGT8F328P MCU:             25.2V

Note: The Chinese manufacturers interchangeably label their models as LCR-T7, LCR-TC1, or LCR-TC2.The only way to identify “what is inside the plastic box” is from a photo of the PC board. However the vendors don’t provide photos of the PC boards.

While I appreciate the thought a diode sort of burned itself in two and it's next to some very unhealthy looking components, I accidentally scraped the diode off trying to clean it up a bit and see what it was and yeah it's bad...

No idea why this happened either, I've been treating it right!

[elecdonia]

While I appreciate the thought a diode sort of burned itself in two and it's next to some very unhealthy looking components, I accidentally scraped the diode off trying to clean it up a bit and see what it was and yeah it's bad...

No idea why this happened either, I've been treating it right!

I bet you have the same (very poorly designed) LCR-Txx model that I received a couple of months ago. Does the area where the PC board has bad (cooked) components look like the attached photo? And is the toasted diode labeled D2?

[GraemeG]

I have just received a "TC1" of this latest design elecdonia. Within a couple of days it failed while testing a few zeners and schottky diodes on the K-A terminals. After the failure it would always show a 4.1V zener across the K-A terminals and when I opened the box it was obvious that D2 was burned.

I was able to find a replacement SMD diode for D2 and it was soon working again but I noticed whenever I tested a zener diode both the zener and D2 would get very hot. Apparently there is nothing to limit the current through D2 and the tested device other than the ability of the DC-DC converter circuit to supply current!

I found a solution on another site (that I now can't find) that suggested cutting the track between C14 and the K terminal and inserting a 4K7 resistor. This limits the current to about 6-7mA even into a short circuit on K-A. This seems to work perfectly! Originally I tried a 10K resistor but the voltage drop was a bit too much and the tester identified it as a zener of about 27V. With the 4K7 resistor the open circuit K-A voltage is 29.7V and this is high enough that the detector assumes no zener is connected.

With an oscilloscope I also noticed that the test voltage was not very well filtered with about 1V peak-peak of 1kHz ripple. I added a 1uF 50V low ESR electrolytic from the K terminal to ground and this dramatically reduced the ripple but to be honest I'm not sure it changed the test results very much. I have tested several zeners now and there is no sign of over heating. The test results seem to be low by perhaps 0.3-0.6V but it's a bit difficult to be sure as there is some variation in diodes and the voltage does depend a little on the test current. In any case it is near enough to give a good/bad indication and if I open the box again some time I might tweak the voltage divider to give a slightly better result.

The bottom line is that every tester of this latest design is almost certain to fail when testing zeners, particularly low voltage zeners and or diodes.

[elecdonia]

I have just received a "TC1" of this latest design elecdonia. Within a couple of days it failed while testing a few zeners and schottky diodes on the K-A terminals. After the failure it would always show a 4.1V zener across the K-A terminals and when I opened the box it was obvious that D2 was burned.

This failure will occur sooner or later to every LCR-TXx unit having this PC board design where the 30V power source rail connects directly to the test socket K terminal.  This manufacturer really “went their own way” with both hardware and software. Unlike the original OSHW Transistor Tester zener test circuit, which has a “step-up switching voltage regulator” IC generating a steady 30V rail followed by a 10K series resistor, this manufacturer substituted a “step-up constant-current LED driver” IC. Their main mistake is they failed to place a proper series resistor >2K2 ohms between the 30V rail and pin K.

I was able to find a replacement SMD diode for D2 and it was soon working again but I noticed whenever I tested a zener diode both the zener and D2 would get very hot. Apparently there is nothing to limit the current through D2 and the tested device other than the ability of the DC-DC converter circuit to supply current!

Here’s what happened: When a zener or a diode (forward-biased) is connected between K-A while the tester is in a powered up state, this damages the current sensing input pin of the step-up IC (U7 on PC board). Actually any electronic component with low resistance <1K ohms or a capacitor with low ESR could cause this failure. This pin on the step-up IC (U7) has a maximum input voltage of 4V. This IC pin is connected to the A terminal of the test socket. Worst case is placing a direct short between K and A while the LCR tester is powered up with the LCD screen turned on. There is a filter capacitor (C14) on the 30V rail (K on test socket). C14 carries a 30V charge. Making a short circuit from K-A dumps all the energy stored inside C14 straight into the current sensing pin of the step-up IC. Although the duration may be brief, 30V is a lot more than 4V. In many cases only the current sensing portion of U7 gets destroyed. The rest of U7 continues to operate, generating 30V without any current limiting. This allows the peak current up to 500mA  through K-A. This is why a zener under test can get extremely hot almost instantaneously.

I found a solution on another site (that I now can't find) that suggested cutting the track between C14 and the K terminal and inserting a 4K7 resistor.

I used a 2K2 series resistor in my unit. If the series resistance is larger the tester may report that a zener is being tested while the K-A pins are open-circuit. A value of 2K2 is sufficient to protect U7 from damage.

To conclude, the fix is:
1) Cut the PC board foil leading to pin K and then connect 2K2 resistor from junction of D2 and C14 to pin K,
2) Replace U7
3) Replace D2 if faulty or burned
4) Check that open circuit voltage from K to A is approximately 30V
5) Place a 1K resistor across K-A and confirm that tester identifies this as a 5 to 7V zener.

[GraemeG]

this manufacturer substituted a “step-up constant-current LED driver” IC.

Thanks for this, I had not checked out the DC-DC converter circuit and did not realise the design change they had made. It is likely that the current sensing input is damaged on my device but it is still generating about 31.5V on C14 so with a new D2 and the extra resistor before the K terminal I still have a working circuit 

A 1K resistor between K and A reads as a 5.2V zener but this is with the 4K7 resistor that I used instead of the 2K2 you recommend. If I have it open again some time I might change the resistor as I am not sure how close I am to the threshold where the code decides a zener is connected to the K-A terminals. The built in battery is currently 3.87V and the zener circuit with 4K7 resistor is producing 29.7V on open circuit K-A terminals but this may drop as the battery discharges. Time will tell!

[alex_D]

Just bought a tester marked Multi-function Tester - TC1 from ebay.
It is never able to test any component but it does boot up ok and the display is ok.

It doesn't recognise any components in the 1,2,3 sockets, it just displays "unknown or damaged part" after
pressing the start button.

I have tried a lot of other simple components and I get the same result.
If I put a diode in the (K, A) part of the socket it does recognise it as a zener, so it seems to be stuck in zener mode.

It has a blue PCB with no transformer, uploaded a photo. On the clones table it looks like a TC1(2), but can't find
a schematic anywhere. cant see any damage on the pcb.

I just got the tester for resistors, capacitors and transistors and I don't need the zener function which seems
to be problematic in any case.

Anyone know how to completely remove and disable the zener testing function?

[madires]

If your TC1 doesn't detect any component connected the standard test pins then it's obviously broken. Have you notified the seller and asked for a replacement? In case of a genuine ATmega you can try an OSHW firmware and run the selft-test to check the test pins. The OSHW firmware can also be customized, e.g. disabling the Zener check.

[Messtechniker]

I think its time to put out a strong warning
about fake transistor testers.
The good times are definitely over.

[indman]

In case of a genuine ATmega you can try an OSHW firmware and run the selft-test to check the test pins.

Madires, this is not a genuine ATmega.This clone variant is built on LGT8F328.I also advise the clone owner to contact the seller with a complaint about a faulty device.In addition, I see a lot of traces of flux on the board, which can negatively affect the quality of work.

[alex_D]

Thanks for the info. I have already got a refund from the seller and they let me keep the fake box, so I will play with it later.
I have ordered a DIY kit tester instead so hopefully I will have more luck with this.