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I have a Camxtool v3.5 CNC controller (similar to this, although this is v3.4) that has an unmarked IC that I haven't been able to identify:

Unmarked IC

The IC is connected between pin PB3 of the ATmega328P (used as a PWM output) and a photocoupler (EL357N). The output of the photocoupler then connects to a N-channel MOSFET used to control the speed of the CNC spindle.

I also found an schematic (which I guess is not official) that shows how everything is connected, but does not identify the IC:

Schematic

The schematic shows a NOT gate to negate the PWM signal before the photocoupler. Does anyone know this specific IC?

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    \$\begingroup\$ looks like there is a sticker on top of the IC \$\endgroup\$
    – jsotola
    Commented Apr 26 at 22:07
  • \$\begingroup\$ I double checked and it is not a sticker. \$\endgroup\$
    – puq_87
    Commented Apr 27 at 1:12
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    \$\begingroup\$ The markings may have been intentionally removed to hinder reverse engineering. \$\endgroup\$
    – Math Keeps Me Busy
    Commented Apr 27 at 1:57
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    \$\begingroup\$ There's various dirt all over the PCB so in case you are trying to repair it, start with isopropyl and clean it. And if it's metallic dust/dust with metal particles, then anything can happen. \$\endgroup\$
    – Lundin
    Commented Apr 29 at 11:36

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On my board the marking is not completely deleted. With some effort I read STC 15F104W, it appears to be a little microcontroller.

Here is a link to a datasheet for the STC15F101 serie which include the STC15F104 too.

It is a microcontroller based on 1T architecture 80C51 CPU.

This is a copy of the pinning from the datasheet, which matches the used pins: enter image description here

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    \$\begingroup\$ Welcome to SE/EE! Please take the tour to learn more about this site, and you might want to read some of the help center. -- Your answer seems to identify the IC correctly. Would you mind to edit it to extend it with a bit more information, like a link to a data sheet and pinning details? \$\endgroup\$
    – the busybee
    Commented Sep 3 at 5:29

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