Products > Test Equipment
TC1 lcr-meter transistor-tester fix
madires:
I don't know the specific current draw for that model, but usually it's about 15mA on average for the 5V rail.
mtcaus:
TC1 will very likely break down after continuous tests in a short period of time because it always generate high voltage for zener diode test every time. The components along that path simply cannot take it. Your unit is the newer design, but it's basically the same. Instead of one transformer with two outputs, your design simply uses two sets of inductors and step-up converters. By looking at the photo, you have a burnt resistor R24 circled in green. You should also check all the components circled in red. I saw your circuit online somewhere before. Just search around and you can find out the value for your R24.
masster:
@mtcaus
Very good catch on R24. It would help to know its value.
I can't explain myself why the resistor R24 failed. "High voltage" is not 6000 Volts or so, maybe 30 Volts at most, and R24 should be in the kiloohms range. Moreover, I didn't insert any part in the K pin (cathode for Zenner diodes)
I have checked the components marked in red. They are all OK. With a thermal camera, when I press the TEST button, the 78L05 regulator and the 4 capacitors (2 on the input side and 2 on the output side) glow like fire...
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indman:
masster,a malfunction in these clones with certain skills in repair and understanding of the principle of their work is found in a couple of minutes. :) The schematic diagram of your clone will roughly correspond to the scheme on the LCR-T7H, only the numbering of the elements will be different. R24 will correspond to R13 on my circuit and will be 10Kohm.
If you have a heated 7805, then there is a high current consumption.We need to determine the cause.Remove the 7805 from the circuit and check its serviceability separately using an external power supply. Also, temporarily remove the U2 diode assembly(SRV05) and the 6V8A suppressor from the circuit. Then check with the multimeter whether there is a low resistance at the output of the 7805 (3.5 ohms)?
Per Hansson:
--- Quote from: mtcaus on August 10, 2022, 09:32:42 pm ---By looking at the photo, you have a burnt resistor R24 circled in green. You should also check all the components circled in red. I saw your circuit online somewhere before. Just search around and you can find out the value for your R24.
--- End quote ---
Isn't it just installed with the bottom side facing up?
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