LCR-T7 Tester no longer switching ON - Page 1
Forum section: electronics / testgear

author: Satbeginner
author_rank: Regular Contributor
timestamp: August 02, 2018, 08:49:15 am
content: Hi all,I have one of these Chinese LCR T7 testers (the one with build in LiIon battery and ability to test Zener diodes up to 30V), but suddenly it will no longer switch on.Thinking of a bad contact, I opened it up, but it all seems in order, except....There is a 6-pin SMD component next to the small, yellow transformer that is very hot when I try to switch it on.I suppose this is the Step-Up thingy for the High(er) Voltage Zener test?As far as I can see it is marked as U5, being an AL718, but I cannot find any data on this thing?Question: Is there a schema / diagram available for this type of tester showing what type of chip this is?Thanks for any response,Un saludo,Leo

author: Satbeginner
author_rank: Regular Contributor
timestamp: August 02, 2018, 09:14:31 am
content: Hi all,on a Russian site I ust found a possible substitute:http://monitor.net.ru/forum/dc-dc-stepup-info-629278.htmlThey suggest the ALxxx indicates it is a SD6271:https://datasheetspdf.com/pdf-file/1098029/SHOUDING/SD6271/1At least it has the ALxxx markings, and it is a Switch mode Step-Up chip.I will now see if the connections make some sense, like Vin, Enable, Switch-out, feedback, etc.Although the datasheet says it goes to 24V out only, maybe in the T7 they used the transformer to get a higher Zener test voltage than that?To be continued,Leo

author: indman
author_rank: Super Contributor
timestamp: August 02, 2018, 03:10:06 pm
content: Read this subject from the very beginning, it will help you to find malfunction.The schematic LCR-TC1 and LCR-TC7 coincide, except for some details.https://www.eevblog.com/forum/testgear/tc1-lcr-meter-transistor-tester-fix/msg1622248/#msg1622248

author: ahmad_hodrob
author_rank: Newbie
timestamp: August 12, 2018, 12:22:22 pm
content: dear Sir,kindly note that I have T7 transistor tester that suddenly stopped working ( no display) upon checking i found that C11 is shorted I replaced it with a 10uf capacitor, know the device is working but it doesn't go to calibration mode even when I connect a 3 short wires to it,even more it reads the short wires as a resistors with a value of about 11 M ohm.please I need an advice and if anybody can help me with the software of the unit.Ahmad_hadrab

author: Satbeginner
author_rank: Regular Contributor
timestamp: September 15, 2018, 11:05:56 am
content: Quote from: indman on August 02, 2018, 03:10:06 pmHi,sorry for my (very!!) late response, but I was waiting for the Switching IC (Type ALxxx) from China.Today they finally arrived, but, after replacing it, it still would not switch on.Long story short, one of the C11 / C12 capacitors developed a short, the remaining one measured around 5n6, so I removed both and replaced them with a 15nF capacitor.It's back working again.Thanks for the tip about the schematics, I don't understand why I did not found this before....Un saludo,Leo

author: madires
author_rank: Super Contributor
timestamp: September 15, 2018, 01:45:43 pm
content: 15nF isn't suitable. A low-ESR electrolytic about 10µF or 22µF and 100V (>=63V) would be much better. It's the filter cap for the 50V DC used for checking Zener diodes. The original MLCCs are borderline because of the maximum voltage rating available for that package size (4.7µF) and the DC bias capacitance derating (known MLCC issue).

author: nitesurfer
author_rank: Newbie
timestamp: July 15, 2019, 09:12:13 am
content: Hello , just new to this forum, just wanted to thank you for the information on T7 LRC repair, Had one unit From a chinese supplier, the unit named TC1 but found that the printed board same as the picture you posted as T7, the unit just suddenly not powering on, through your post got the C10 smd capacitor and tested open line (OL) on the multitester, got it working with replacement of a 10nf smd capacitor, many thanks though the cost of the tester is not much, time of order of the tester on my location will take almost 45 days.

author: Robertr
author_rank: Newbie
timestamp: January 26, 2020, 06:56:49 am
content: I tried to measure a 9 volt battery with a T7, now it won't turn on. (smile don't do that). I've checked all the diodes, resistors and capacitors already mentioned. Anyone have any suggestion of what I likely popped? Please and thank you in advance.I feel bloody stupid over this and stubbornly want to fix it.

author: madires
author_rank: Super Contributor
timestamp: January 26, 2020, 02:39:59 pm
content: Did you measure the battery via the standard test pins 1-3 or the test pins for the Zener check A & K?

author: Matt@TYGA
author_rank: Newbie
timestamp: June 06, 2022, 06:47:20 pm
content: Hi guysJust bought a T7 tester. But it won't calibrate. Short pins 1,2 & 3 with the cheesy thing supplied and it just shows a restance of around 0.25 ohms. Can anything be done?

author: madires
author_rank: Super Contributor
timestamp: June 07, 2022, 09:26:24 am
content: You could try to wiggle the short-circuit-thing to get a better contact or try a short wire instead.

author: Hruki
author_rank: Newbie
timestamp: December 05, 2024, 12:29:08 pm
content: Hi Guys,I have this new generation T7 tester, no longer turns onI'm trying to investigate which component went wrong.Do we have any schematic for this type? I attach two photos.Thanks in advance!Ruki

author: madires
author_rank: Super Contributor
timestamp: December 05, 2024, 12:44:27 pm
content: Your T7's MCU is an LGT8F328, not an ATmega. If you need to replace the MCU you won't get a firmware.

author: Hruki
author_rank: Newbie
timestamp: December 07, 2024, 08:04:25 pm
content: I hope the problem is not with the uC. I'd like to test the other components first, that's why I need the schematic diagram.

author: Harry_22
author_rank: Frequent Contributor
timestamp: December 09, 2024, 01:03:50 am
content: Check the power at MCU first.