| Products > Test Equipment |
| TC1 lcr-meter transistor-tester fix |
| << < (37/80) > >> |
| mtcaus:
Solved the no power up issue. When the button is pressed, there is no display and Step-up/Boost IC at U5 is so hot. It could burn your finger. The fault is the Schottky barrier diode at D2. The diode with marking code SS18 (1A, 80V) was tested fine both in-circuit and out-of-circuit. Replaced it with SR2100 (2A, 100V) and the unit is working again. Measured the peak voltage of 52V at the cathode side of SR2100 Schottky diode when the button is pressed. Since the voltage rating of 1206 SMD capacitor at C11 is only 50V. Eventually C11 will give up. I replaced it with an electrolytic capacitor Rubycon 4.7uF @50v. I couldn't find a higher rated voltage of capacitor. Ideally should be like 100v. However, when I tested the Rubycon withstand voltage, it could go up to 100v. No wonder Rubycon capacitors are good. Anyway, fixed the unit by replaced two components at D2 and C11. See photo fixed.jpg. From the transformer, when the button is pressed, there are two outputs, 9v (for powering the unit) and 37v(at least for Zener diode testing). See photo Bottom.jpg. Mine was like 2v on either path. Obviously there was a short somewhere. Through the process of elimination, I removed Schottky diode first. I got the 9V back. At first I thought ATMEGA324PA was the fault, but it was tested fine when applying 5V directly. See photo Top1.jpg and Top2.jpg. At first replaced D2 with SS24(2A, 40V) for testing. Obviously the voltage is not rated high enough. The diode was so hot and high pitch sound can be heard from the transformer when power up. Since I don't have any other SMD Schottky diode with a voltage rated that high. I used a through-hole Schottky diode SR2100 and there is enough space to install it. For the capacitor at C11, it will give up eventually if the peak voltage repeatedly go above the rated 50v 1206 SMD capacitor. This maybe the reason why people reported C11 shorted in the forum. My LCR-TC1 is from the original creator. The original has 3 Chinese characters (浩祺心) on the top of the circuit board. See photo Top1.jpg. The component layout may be slightly different than yours since there are so many clones out there. However, the general layout is the same. I have been troubleshooting this unit for a while. Replaced numerous Step-up/Boost IC ALxxx at U5 with different numbers. xxx are three numbers. The numbers do not matter if anyone who cares to know. Even bought STC15L104W chip at U4 and programmed it. By the way, I couldn't find the original U4 firmware. Luckily I didn't overwrite the original chip. Obviously none of them worked until I replaced Schottky diode at D2. The time and money spent may not justify, but the feeling of successfully fixed the unit is worth it. Hope this post will help someone out there. |
| masster:
I bought today my TC1. As many other users before me, I calibrated the tester then started to check parts. After maybe 8 parts measured, the tester turned off as usual by himself, but never came back on. It is dead. I didn't check any capacitor, only resistors, transistors, and a diode. I thought the battery is low, although the tester showed 3.85V. I charged it on USB and after 10 minutes the LED turned from red to green. Yet still no luck. The tester is dead. Full of confidence, I opened the case, hoping to change two capacitors and move on. But... surprise! Although on the outside, my TC1 looks identical to the rest of TC1's in this topic, on the inside there is another story. A totally different parts layout. See attached photo. I managed to read the codes on each IC and annotated the photo accordingly. So my question is: how should I diagnose for the fault? Anyone happens to have the schematic for this version? Many thanks in advance if you can help me. |
| masster:
Update: The output of 78L05 (VCC) is shorted (3.5 ohms). What is the best method to decide which component is shorted? Capacitors, input protections, IR receiver, MCU, ATMEGA itself. |
| TurboTom:
If you have a thermal imager, attach a current limited lab supply to the shorted supply line (set to maybe 100mA) and observe what component heats up. This is also possible without such gear: if you use a sprayer (the type used for misting flowers) filled with isopropanol or ethanol and spray the board with a very thin layer of the liquid, you can usually observe where it evaporates first. Good luck! |
| masster:
78L05 has a maximum output current of 100mA with proper heat dissipation. How much current draws the device on 5V when measuring? |
| Navigation |
| Message Index |
| Next page |
| Previous page |