$20 LCR ESR Transistor checker project

[elecdonia]

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.

Have you performed the “self-adjustment” procedure?
Do this by shorting test socket pins 1, 2, 3. The metallic strip of 3 crimp pins supplied with these LCR-Txx units can be used for this. Take care to place it so that it shorts pins labeled 1-2-3. Then press the button. It should display “self test.” After 10-30 seconds it should display “isolate probes.” Now pull out the short circuit and it should eventually display “test complete.”

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.

If your tester displays “unknown or damaged part” then it isn’t stuck in zener test mode.

It has a blue PCB with no transformer, uploaded a photo.

The unit in your photo is likely to be a clone using the LGT8F328P MCU.

Unfortunately the software is proprietary and cannot be upgraded. Eventually the open-source Transistor Tester software might get ported to the LGT8F328P MCU, but I’m not expecting this anytime soon. Note: The LGT8F328P claims to be an improved version of the Atmel ATmega328P. However it isn’t fully compatible at either the hardware (different pinout) or software level. This MCU is made by a Chinese semiconductor company named “LogicGreen.”

I have a similar unit with LGT8F328P MCU. It functions but has issues (inaccurate for some types of transistors). It does measure resistors, capacitors, and inductors reasonably well.

I discovered a way to identify units with LGT8F328P MCU: Press and hold down the button for 30 or more seconds. The display language should switch from English to Chinese. Wait till tester times out and powers off, then press and hold the button for another 30+ seconds to switch back to English.

[alex_D]

Yes I tried the self test and just got the “unknown or damaged part” message. After pressing Start testing across the 1,2,3 pins gives 0 volts. testing across K,A gives 25.4v. Do you know what voltage I should get across the 1,2,3 pins after pressing the start button?

Thinking that there could be a bad connection to the test pins somewhere, might try working my way back re-soldering the joints. other than this thinking the 6 pin V05 (D2) might need swapping.

Yes, if I press the Start button for around 30 seconds the language does change to Chinese.

[Feliciano]

If you have an oscilloscope at hand, you could try to see whether there are pulses on the 123 positions when you press the test button.
With a DMM you could double check the continuity of the traces.
If the MCU is damaged, there's nothing more to do.

[elecdonia]

Yes I tried the self test and just got the “unknown or damaged part” message. After pressing Start testing across the 1,2,3 pins gives 0 volts. testing across K,A gives 25.4v. Do you know what voltage I should get across the 1,2,3 pins after pressing the start button?

OK, I will post the voltages from my LCR-TC1 which contains the LGT8F328P MCU. Its PC board is similar to yours.

Thinking that there could be a bad connection to the test pins somewhere, might try working my way back re-soldering the joints.

My experience is that shorts from solder bridges occur more often than open circuits from dry joints. I recommend a close visual inspection with a strong magnifier, microscope, or close-up photos taken by smartphone.

…other than this thinking the 6 pin V05 (D2) might need swapping.

When V05 failed in another of my Transistor Testers (different model) the display was “CELL” for one of the pins. I don’t recall which pin or the exact voltage reported by the “CELL” display message. FYI, “CELL” normally gets displayed when the tester software detects that a battery has been connected to the test pins. In my case V05 failed when I accidentally connected a charged capacitor. Replacing V05 fixed my tester.

Yes, if I press the Start button for around 30 seconds the language does change to Chinese.

This confirms you have the version with LogicGreen LGT8F328P MCU.

[alex_D]

Put the scope on the 1,2,3 pins, after pressing start I get a short series of pulses at 5 volts, except between pins 2 and 3 where I get 0 volts.

With the battery disconnected did a continuity test between 2 and 3 and have a short in both directions, can't see any obvious short, so I'll
need to trace the tracks and maybe try to draw a schematic, need to get a pinout for the MCU. At least PCB seems to have a 10k series resistor for
the K pin.

The short could be under the ZIF or the 6 pinV05, or a damaged MCU, at least the infra red remote test works ok.  lol.

[zzika]

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
...

Could you please tell me which step-up IC (U7) it is?

The marking on the my chip is  HYEQG.

Where can I buy those step-up IC?

[GraemeG]

I don't know what chip U7 is but looking at your board D2 shows no sign of burning or heat. If you still measure 28-32V on the K-A pins with no component connected then U7 is still working and all you need to do is to cut the track between C14 and the K terminal and insert a 2K2 resistor. Once this change has been made this version of the tester seems to work well.

[zzika]

I don't know what chip U7 is but looking at your board D2 shows no sign of burning or heat. If you still measure 28-32V on the K-A pins with no component connected then U7 is still working and all you need to do is to cut the track between C14 and the K terminal and insert a 2K2 resistor. Once this change has been made this version of the tester seems to work well.

The voltage on the K-A pins is 4V - the voltage of the Ni-Mh battery.

I need to replace U7 but I can't find which circuit it is.

[indman]

zzika, it is advisable for you to read this topic carefully or use the search system for the necessary information on the forum. Information about the U7 chip has already been discussed in this topic:
U7 - this is SY7200A (marking HY6VE)

[zzika]

This topic has 328 pages. Before asking the question I tried reading the discussions to find an answer, but without success. The search system could not find a suitable post for me according to the parameters I had.

Thank you for your response. I already ordered the SY7200A so if anyone needs info I'll leave a message here if everything is working as it should.

[indman]

Before asking the question I tried reading the discussions to find an answer, but without success. The search system could not find a suitable post for me according to the parameters I had.

In the screenshots below, I show you that the search engine on this forum is working fine.

[RoGeorge]

LOL, thanks, I didn't know that button either. 
Was using Google with site:eevblog.com appended in the search terms.

[py-bb]

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?

Sorry for late reply, you're exactly right it's that bit. My diode was far more visibly cooked though it'd basically popped in half.

Any recommendations on getting a long and happy life out of the replacements? I apologise you clearly know a lot about the model and I regret treating mine as screwed (I used it for heatgun practice)

[elecdonia]

The short could be under the ZIF or the 6 pinV05, or a damaged MCU, at least the infra red remote test works ok.  lol.

Check very closely for solder bridges at all locations where the PC board foils for test socket terminals 2 and 3 connect to the MCU, to the V05 protection device, and to the group of 680R and 470K resistors. You will need a microscope or a strong magnifier. These pins 2 and 3 connect straight to 2 pins on the MCU which may be right next to each other. Even if you don’t find a visible solder bridge it is a good idea to reheat these IC pins after applying solder flux to them. The solder flux is the important part: Flux permits solder bridges to separate when the solder melts. If you find a big blob of solder anywhere then use desoldering wick to absorb the excess. I recently learned to add additional solder flux to the desoldering wick before using it. Even though the wick already contains flux, “everything works better with extra flux” when correcting solder bridges.

If there aren’t any solder bridges then I suggest removing the V05 protection IC as the next step. Although V05 is rated at 10A peak current it isn’t totally bulletproof. It is safe to operate the transistor tester with V05 removed as long as you are careful to discharge capacitors before testing them. If V05 is the culprit then get another one and replace it before using the tester heavily. I have a tester where V05 did fail. Everything worked again after removing the faulty V05. It sacrificed itself to save the MCU.

A short underneath or inside the ZIF test socket is unlikely but if nothing else clears the short between pins 2 and 3 then I recommend desoldering and removing the ZIF socket. There is a first time for every failure.

Here’s the most important thing: Your transistor tester has a direct short between ZIF pins 2 and 3. But this isn’t a short to ground or +5V is it(please confirm)? When an IC fails it will often have pins shorted to ground or VCC (+5V in this case). It isn’t likely for 2 pins of an IC to short to each other without also being shorted to ground or VCC.

Summary: If the only short in your unit is between pin 2 and pin 3 this means there are only a small number of causes for this fault.

[elecdonia]

Any recommendations on getting a long and happy life out of the replacements? I apologise you clearly know a lot about the model and I regret treating mine as screwed (I used it for heatgun practice)

Replace diode D2 and step-up IC U7. Add a 2K2 series resistor between the junction of D2/C14 and the K pin of the ZIF socket. This requires cutting the PC board foil between these two points. Doing this will make the zener testing circuit unbreakable.

It’s a pity the manufacturer neglected to include the 2K2 series resistor.

[elecdonia]

Put the scope on the 1,2,3 pins, after pressing start I get a short series of pulses at 5 volts, except between pins 2 and 3 where I get 0 volts.

Are pins 2 and 3 both shorted to ground?

[alex_D]

Sorry yes, pins 2 and 3 are shorted to ground, so likely no short under the ZIF.

I guess that likely means V05 is bad?

[Feliciano]

I guess that likely means V05 is bad?

Maybe. You can remove it and mesure again.

[elecdonia]

Sorry yes, pins 2 and 3 are shorted to ground, so likely no short under the ZIF. I guess that likely means V05 is bad?

It is very likely that V05 failed. Try removing it.

[alex_D]

Removed V05, but the short still exists, it must be a defective MCU, reached the end of the road with this clone box.
Anyway I've got a AY-AT kit on the way with loads more options, so no loss 

[Feliciano]

A final test you can do: cut a trace and measure the ports directly.

And you can save the protection IC for future use.

[elecdonia]

Removed V05, but the short still exists, it must be a defective MCU, reached the end of the road with this clone box. Anyway I've got a AY-AT kit on the way with loads more options, so no loss 

I recently bought an AY-AT kit. For years I’ve had a factory-built AY-AT. It has served me well. In fact it is getting a bit shabby from years of daily use.

Because these AY-AT kits are so cheap ($10-12 USD) I decided to get one. I’ve assembled my AY-AT kit and am beginning to test it.

In addition I fired up my MCU programming kit in order to try out different TransistorTester firmwares. My programming device is an Arduino UNO loaded with the standard “Arduino as ISP” sketch. I recently obtained a nifty programming shield for it which has a ZIF socket. Another cool item I just started using is the superb AVRDUDESS GUI front-end app for AVRDUDE. Wow! It makes programming chores much faster and easier!

At this time my two AY-AT units are still running their original Asian factory firmware. Both are a modified 1.12k. Each is slightly different. The older unit has fewer items in the user menu compared to my new AY-AT kit. Unfortunately the MCU flash is locked in my older unit so I won’t be able to directly compare flash contents. However the ATmega328P which came with my new AY-AT kit is unlocked. I’ve already grabbed the contents of its flash and EEPROM.

My next task is to get both of them to run the 1.13k firmware. I have a whole tube of brand-new ATmega328P. Both of my AY-AT units have a socket for the MCU, making it very easy to swap different firmwares.

[alex_D]

A final test you can do: cut a trace and measure the ports directly.

Yes I did cut the trace next to the MCU at pin 24, I can confirm 100% the short is at the MCU.

Is it worth swapping out the MCU for a real ATMega? probably not. would it work with this clone board?
then I would need to program the replacement with the open source firmware, I'll keep the box in case I try to give it a go. 

[alex_D]

Removed V05, but the short still exists, it must be a defective MCU, reached the end of the road with this clone box. Anyway I've got a AY-AT kit on the way with loads more options, so no loss 

I recently bought an AY-AT kit. For years I’ve had a factory-built AY-AT. It has served me well. In fact it is getting a bit shabby from years of daily use.

Because these AY-AT kits are so cheap ($10-12 USD) I decided to get one. I’ve assembled my AY-AT kit and am beginning to test it.

AY-AT kit looks like a good choice then. I noticed there are a few upgrades you can do like swapping out the crystal, and upgrading the voltage regulator.

[Feliciano]

Is it worth swapping out the MCU for a real ATMega? probably not. would it work with this clone board?
then I would need to program the replacement with the open source firmware, I'll keep the box in case I try to give it a go. 

As elecdonia recently mentioned, there are at least 3 kinds of alternate MCUs for this series of ctester. If you modify the pinout for a valid ATmega, you could swap the damaged MCU, but you would also need to replace the power controller MCU with a circuit previously described in this thread, and program the new ATmega with the m-firmware. Would it worth it? For me, if the options were throw it away, or rescue it for few pounds, I would proceed and later rejoice.