$20 LCR ESR Transistor checker project

[elecdonia]

Right now from my experience, it seems the best option is to get the self build kit, that way you can be sure of getting a component tester you can easily self repair, mod and upgrade the firmware.

I recently purchased one of these kits. It is a "through-hole" PC board  using a DIP package ATmega328P mounted in a socket.

It had just one significant issue: The 680 ohm and 470k ohm "probe resistors" supplied with the kit were out of spec.

Specifically one 680 ohm resistor measured 691 ohms compared to the other two (675 and 676 ohms). The error is 1.6%
Unfortunately this prevented my tester from entering the "self-test" mode. It failed to detect that the probes had been shorted to start the self-test.

Re-reading this topic revealed these frequent instructions from the experts:

     "make sure your 680 ohm and 470k resistors are well-matched within 0.1%."

For a "quick fix" I put a 33k resistor in parallel with the out-of-spec 691 ohm resistor. The result is 677 ohms.
This immediately permitted "self-test" to operate.
My tester now works perfectly.

I do recommend these kits for people who are comfortable soldering "through-hole" PC boards.
There is no chance of getting a "fake" DIP package ATmega328P because nobody but Atmel/Microchip makes them.
Also having the MCU in a socket makes firmware upgrades and experimentation quick and easy.
And it is feasible to replace those crummy original resistors with ultra-high precision resistors.

[Messtechniker]

Moreover, if you kill the MCU with a charged capacitor,
you can in this case simply replace the MCU. 

[GraemeG]

Right now from my experience, it seems the best option is to get the self build kit, that way you can be sure of getting a component tester you can easily self repair, mod and upgrade the firmware.

Alex did your kit come with the clear plastic case or does this need to be ordered separately?

[alex_D]

My kit didn't come with case, I ordered it later. There are 2 types of plastic clear case, I got the angled one with space for the 9v battery underneath.
It's worth mounting the ZIF socket in a regular DIL socket since it raises a bit so you can operate the handle better.

I flipped around the 2 bottom terminals underneath so I could easily get at the protection diode if I ever need to swap it out.
I tested out all the resistors before I assembled the kit and found 4 were the wrong value and couldn't be used, not a big deal as I had the missing values
in my spares box.

I mounted the power connector for the battery underneath so making the wire routing easier. I also got a spare Atmega so I could program it on
a breadboard. The kit is worth it just for the PCB and the MCU alone.

[Pukker]

@ GraemeG.

Yes that case works fine.
I have made an modification to acces the SMD Pad
and easier to move the handle of the Zif-socket.
See post 2673

[GraemeG]

Thanks Alex and Pukker. I hadn't seen the angled case before and I like the idea of a built in 9V battery.

I also think I would modify the case as you did Pukker although I don't do much SMD work. Perhaps lifting the ZIF socket with a normal DIL socket is a simpler option although I would prefer soldered connections. Has anyone had problems with the ZIF or the MCU being mounted in sockets? The contact resistance should be low but I wonder if it could affect any of the measurements.

[madires]

I'd recommend to use precision sockets. Cheap ones tend to cause connection problems after a while, especially when the ZIF is a bit wiggly (no tight fit allows movement of the ZIF).

[davidut5]

Got new tester lcr-tc1, first measurement capacitor in zener diode kaa probes got some charge then moved to 1-2, tester got damaged.
Bought new mega328PB, 328p not available, read about pin 3 and 6, pin 6 not connected and pin 3 connected to ch340n pin 7.
5v ok when mega328 removed, but when in place after pushing start it gets very hot in short time and have to remove the battery to stop. No software on yet, but getting hot i think is not software related. Cut the circuit to pin 3 still getting hot. Resistance on 6v8 diode is 400k.
And about firmware, was looking for original, nothing fancy just need it to work. Managed to repair another lcr t4, replacing the mega328p, using avrdudes but for this did not find original firmware to download, just modified.
I am confused, board gives power only on pins 18(gnd) and 19(vcc), but datasheet say pins 3 and 4! I think the chip has wrong markings on it, probably on purpose. there is also no oscillator on board. What kind of chip this could be? Atmega3208 maybe?
In the picture not 100% but the one on the right is from tc1 and the left from t4.
Thank you.

[smg]

Delivered my T7 with a clone Mega328,
pcb similar to LCR-TC1(2) from the file TableClonesEN.pdf by indman@EEVblog
https://yadi.sk/d/yW8xa5NJgUo5z

[madires]

I am confused, board gives power only on pins 18(gnd) and 19(vcc), but datasheet say pins 3 and 4! I think the chip has wrong markings on it, probably on purpose. there is also no oscillator on board.

Most likely the MCU the clone came with is an APT32F172K8T6 with fake ATmega marking. Sadly we see more and more of those.

[davidut5]

Very disappointing, the mega328 was almost 1/4 the price of the tc1 tester and now not getting it to work any time soon!
I get it there is no firmware available for it yet, or the chip not available to buy!
Clone tester with a clone chip from a clone! 
Hope the mega328pb is still ok, to keep for the t4, just in case another charged cap comes around!

[Aldo22]

What kind of chip this could be? Atmega3208 maybe?

I have exactly the same circuit board and mine has a APT32F172K8T6 on it.
So I guess yours is a APT32F172K8T6 too.

[alex_D]

I'd recommend to use precision sockets. Cheap ones tend to cause connection problems after a while, especially when the ZIF is a bit wiggly (no tight fit allows movement of the ZIF).

This is what the Hiland M644 uses, pity you can't get a through-hole kit or PCB for this M644 layout  ;-)

[MrSqueaky]

Very disappointing, the mega328 was almost 1/4 the price of the tc1 tester and now not getting it to work any time soon!
I get it there is no firmware available for it yet, or the chip not available to buy!
Clone tester with a clone chip from a clone! 
Hope the mega328pb is still ok, to keep for the t4, just in case another charged cap comes around!

A 5V Arduino Pro Mini glued on to the nice big ground plane and lots of enamelled jumper wires and it'll be good as new 

There seems to be a ~US$5 price difference between the LCR-TC1 and LCR-TC2 on Aliexpress. I'm guessing that covers the price of a real Atmel chip

[elecdonia]

There seems to be a ~US$5 price difference between the LCR-TC1 and LCR-TC2 on Aliexpress. I'm guessing that covers the price of a real Atmel chip

BINGO! Spot-on!  

[Thelmos]

I just received a LCR-TC2 from China...

I didn't like the first test, short-circuiting the three pins didn't launch the calibration, it directly measures the short-circuit resistance, from what I've read in this thread this may be because the resistors are out of spec (https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4726172/#msg4726172).

The manual doesn't even mention how to do the calibration.

I have also done the test that @elecdonia mentioned in https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4692413/#msg4692413, results: 12.68V 

Seeing the board, my fears have come true...

[MrSqueaky]

I just received a LCR-TC2 from China...

Looks like cost cutting has finally caught up to the LCR-TC2 (PCB labelled T7-PLUS V2.0) or it a knock off. What markings are on the MCU? It is not a ATMega324 (pin count wrong) and not a ATMega328P (power pins don't match). Some sort of clone chip.

The circuit for the zener diode voltage appears OK (U7, R18, R19, L2, D4, C15). R20 should limit the current. The voltage between D4 and R20 should be around 27V

The 6V8 TVS diode has been omitted. Smaller crystal. Configurable power-off time is back. There appears to be a little push button (?) in the bottom left labelled "OFF" for manual shutoff? Strange

[elecdonia]

I just received a LCR-TC2 from China...  I didn't like the first test, short-circuiting the three pins didn't launch the calibration, it directly measures the short-circuit resistance, from what I've read in this thread this may be because the resistors are out of spec Seeing the board, my fears have come true...

Your LCR-TC2 is likely to contain the LGT8F328P MCU chip. This is a Chinese “?clone?” of the Atmel ATmega328P MCU. However the pinout is different. Also the architecture is sufficiently different enough to require a rewrite of the existing TransistorTester firmware. Check out these other posts for more info:

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4316005/?topicseen#msg4316005

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4606612/?topicseen#msg4606612

As for the failure of your tester to enter the “self test” you should measure the resistance of the three 680 ohm resistors which connect from the MCU to test terminals 1, 2, and 3. These 3 resistors must be matched to each other within 0.1%. I fixed a similar issue by adding a parallel resistor to one of the 680 ohm resistors which was above its proper value by +1.8%

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4726172/?topicseen#msg4726172

[elecdonia]

Delivered my T7 with a clone Mega328, pcb similar to LCR-TC1(2) from the file TableClonesEN.pdf by indman@EEVblog
https://yadi.sk/d/yW8xa5NJgUo5z

The MCU chip in your LCR-T7 is the LGT8F328P made by a Chinese company known as “Logic Green.” It is somewhat similar to the Atmel ATmega328P, but it certainly isn’t a direct replacement. First of all the pinout is different. More important, its architecture and software are considerably different. Furthermore it doesn’t support the Atmel “ICSP” (aka “ISP”) programming interface.

Here are some related EEVBlog topics discussing the LGT8F328P:

https://www.eevblog.com/forum/microcontrollers/arduino-pro-mini-two-copies-have-different-sleep-currents/msg3184622/#msg3184622

https://www.eevblog.com/forum/projects/anyone-here-interested-in-the-logic-green-avrs-lgt8f328p/msg2717650/#msg2717650

https://www.eevblog.com/forum/microcontrollers/lgt8f328p-clone-of-atmega328-with-lots-of-extras-anybody-use-them/

[elecdonia]

Very disappointing, the mega328 was almost 1/4 the price of the tc1 tester and now not getting it to work any time soon!  I get it there is no firmware available for it yet, or the chip not available to buy!
Clone tester with a clone chip from a clone! 

Hope the mega328pb is still ok, to keep for the t4, just in case another charged cap comes around!

At least the manufacturer of this particular Transistor Tester was ethical enough to keep the original APT32F172K8T6 label on the MCU chip.

A couple of months ago I received a Transistor Tester where the APT32F172K8T6 device had been deliberately re-labeled as Atmel ATmega328P.   

[elecdonia]

Let's say we received a new Chinese T7 clone, a TQFP32 MCU without any marks @16MHz. Is there any way to make an educated guess on what knock-off it can be, LGT8F328P or other?

If there is a crystal mounted on the PC board next to the MCU chip:   Then MCU is Lucky Green LGT8F328P

If there is no crystal on the PC board:   Then MCU is APT32F172K8T6. Evidently this MCU has internal clock oscillator

Note: During the past several months I have seen and tested several recently manufactured  “LCR-x” Transistor testers.
None of these units with the MCU chip in a 32-pin TQFP package contain the Atmel ATmega328P MCU.
However, some of these 32-pin MCU chips did have realistic looking (counterfeit) ATMega328P  labels laser engraved on them.

I recently bought one LCR-x unit with a real ATmega324 in a 44-pin TQFP package. It cost about $9 USD more than the units containing imitation 32-pin MCU chips. To the best of my knowledge none of the low-cost Chinese MCU chips come in 44-pin packages (yet).  So if the MCU has 44-pins it is likely to be a real Atmel ATmega324.

[davidut5]

Yes, i guess 328p does not support infrared and maybe zenner test. That's why they use the 44 pin 324, but now they made their own ic. This was the cheapest lcr-1 tester i can get in my country, probably the other ones had the 324 atmel. Did not think it would be different.

[madires]

You can have the IR receiver/decoder (via the three probes) and the Zener check (usually PC3) with an ATmega328 without any problem.

[alex_D]

If  I had a custom PCB made using AY-AT design but altered the board substituting the ATMega328 with a ATmega1284p package, it should just work right?
assuming I compile the the firmware for the ATmega1284p and I would have 4 times the flash?

[madires]

Yep! But you could make some small changes to improve the display performance:
- move the rotary encoder to dedicated pins
- go for hardware SPI for the display