Products > Test Equipment
LCR-T7 Tester no longer switching ON
Satbeginner:
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
Satbeginner:
Hi all,
on a Russian site I ust found a possible substitute: http://monitor.net.ru/forum/dc-dc-stepup-info-629278.html
They suggest the ALxxx indicates it is a SD6271: https://datasheetspdf.com/pdf-file/1098029/SHOUDING/SD6271/1
At 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
indman:
Read this subject from the very beginning, it will help you to find malfunction. :D
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
ahmad_hodrob:
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
Satbeginner:
--- Quote from: indman on August 02, 2018, 03:10:06 pm ---Read this subject from the very beginning, it will help you to find malfunction. :D
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
--- End quote ---
Hi,
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.... :palm: :palm:
Un saludo,
Leo
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