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TC1 lcr-meter transistor-tester fix
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gianb_diazm:
Hello again and thanks in advance,

Even though the boards are identical, mine has a real ATmega 328P, instead of that U1 chip on the picture I linked to. I didn't catch the difference until after indman pointed it out.
Also, I removed U7 and it's still showing Zener. I have removed before, out of desperation more than anything, L1, the R6 and R7 voltage divider, U6, D1, R16, D2, basically anything less than 2 traces away from the KAA probes. In all cases, it shows the Zener test and a random 3.4ish voltage.

I forgot to mention, whenever I short all the 123 probes, the tester goes into selftest mode no problem, so there might be some hope left for the device.
I wouldn't mind losing the Zener functionality as long as the rest of the tester works, as I mostly use it for MOSFETs and the like.
indman:

--- Quote from: gianb_diazm on March 29, 2023, 08:20:29 pm ---Even though the boards are identical, mine has a real ATmega 328P, instead of that U1 chip on the picture I linked to. I didn't catch the difference until after indman pointed it out.

--- End quote ---
Unfortunately, you are mistaken. If you have the same board as I showed in the photo below, then this is not a real ATMEL, but a Chinese fake. In fact, the APT32F172 processor is installed, it’s just a fake marking on the case. This has already been proven 100% and many buyers of similar clones have already successfully won the dispute and returned the wasted money. This Chinese controller is damaged on your board with 99.9% certainty, so return to life this clone is unrealistic. :(
gianb_diazm:
Yes, it's exactly that board, down to the markings on all the chips. A very convincing forgery!

Well, such is life. I guess I'll have to replace the microcontroller then.  :-BROKE

It's a real shame that these MCUs are not reprogrammable, because I could've reused the chip for a digital pins-only project.

Thanks a lot for the help and the patience!  ;D
elecdonia:

--- Quote from: indman on March 30, 2023, 05:35:05 am ---
--- Quote from: gianb_diazm on March 29, 2023, 08:20:29 pm ---Even though the boards are identical, mine has a real ATmega 328P
--- End quote ---
Unfortunately, you are mistaken. If you have the same board as I showed in the photo below, then this is not a real ATMEL, but a Chinese fake. In fact, the APT32F172 processor is installed, it’s just a fake marking on it
--- End quote ---
Two dead give-aways for identifying LCR-Txx units with APT32F172 MCU:
     1)  MCU has 32 pins
     2)  There is no crystal anywhere on the PC board

Other details often found in LCR-Txx units with APT32F172MCU:
          -  A pair of LMV358 dual op-amps at locations U9, U10 (I'm still in the process of learning exactly why these opamps are used)
          -  D2 cathode connected directly to test socket "K" pin for zener diode test. This circuit is guaranteed to fail. Before using the zener test feature the trace between D2 and pin "K" must be cut and a series resistor installed. 2.2k ohms worked well for me.
This is important! DO NOT test zeners before making this series resistor modification!
elecdonia:
Perhaps someone with PC board layout talent will design a small adaptor PC board for replacing the APT32F172 with either ATmega328P or ATmega324?
Although the pinouts are considerably different this still might be feasible.
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