I fried my MTester

[vlad777]

I was mesuring some capacitors, and forgot to discharge them...
Now MTester shows bogus readings, and when nothing is connected shows:  N-E-MOS.
Does anyone have experience with this, a way to fix it, what should I check?
Many thanks.

[tom66]

The circuit is very simple and the microcontroller is directly exposed to the test leads.  Most likely the microcontroller is fried and needs to be replaced.  I damaged my old 3D printer controller board in a similar manner, shorting the bed heater thermistor to +24V.  Whilst the microcontroller "worked" afterwards, all temperature sensor channels read minimum temperature and the controller was effectively dead unable to regulate any of the heater channels.  Replacing the MCU wasn't too hard for that, but the cost of an MTester probably means it's not worth doing.

[vlad777]

Even if I were to replace the uC, I don't have the firmware.
I assume that the firmware in this one is locked.

[CJay]

Think it's highly likely to be using the open source firmware used in hundreds of these type of tester.

[vlad777]

If you have something particular in mind , can you please share a link , github?

[rteodor]

There is quite an active thread on these component testers. Firmware version v1.51m was just released:
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg5228742/#msg5228742

If you decide to get a new one then consider a variant with MCU on a DIP socket like GM328A.

[CJay]

There is quite an active thread on these component testers. Firmware version v1.51m was just released:
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg5228742/#msg5228742

If you decide to get a new one then consider a variant with MCU on a DIP socket like GM328A.

Beat me to it, yes, I think a large percentage of the cheap component testers are based on this firmware

[vlad777]

I found out that pin 24 is damaged. (it is measuring 166ohms to ground when no vcc)
I lifted that pin, so it is now floating
I think I could disable this pin in disassembled hex file, that I found on this forum (my chip is locked).
  https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg5228742/#msg5228742
  https://www.eevblog.com/forum/testgear/lcr-t4-mtester-v2-07-lcr-meter-black-block-issue/
I could change every DDRxn io instruction if I disassemble and reassemble hex file.
So my hope is to recover some functionality like measuring capacitors.

My questions are:
How do I disassemble the hex because gcc objdump -d  doesn't work?
Do I leave the pin floating or attach a resistor to ground, or something else?
How do I reassemble the file? (gcc as )

(Also how do I convert bin to hex because, one out of two files on this forum, is bin?)