/diy/ - Do It Yourself

>>2571765
Ok it is an NE555. Chances are the circuit is like this:
There is an extra resistor and a zener diode, but R3 on your board looks to just be a 0Ω jumper, and ZD1 is probably just there to prevent overvoltage on the MOSFET gate.

If you just remove the potentiometer, then drive a PWM waveform to the middle pin (yellow wire) of the connector, and tie a ~4.7kΩ resistor from the CV pin to ground, you should get what you're after. For that resistor, it shouldn't be too hard to solder to since pin 5 is on the corner of the package (the one opposite the dot), and also is directly connected to what I assume to be C3 as written on your board (C2 on my circuit) so you could probably have a better time just soldering it across C3. Don't forget to tie the 0V of the arduino to the 0V of the PWM circuit also. Breaking/desoldering off the cap written as C4 on your board would be advised.
This is a hack that uses the NE555 just as a MOSFET gate driver. It does invert the PWM signal.

That SR20010LCT is probably just a diode IC package, for freewheeling. Can't find a datasheet, maybe the name is off slightly.