K40 Laser Power supply "Power Adjust" in.

[Detzi]

Hi there,
the supply of my K40 Laser crapped out so i wanted to take the opportunity and upgrade the electronics.

The original configuration uses a potentiometer connected between +5V and GND and the wiper is connected to the "IN" labeled pin on the PWR-Supply. Since the "Datasheet" of the supply states that also a PWM could control this input i did hook up a PWM-Out to this pin.

Now i could notice that this "IN" puts out 5V. Confused as i am i took the thing apart and here i am even more confused asking if someone can explain what is happening here: please have a look at "sch.png" in the attachements.

The Chip used is a TL494CN which error amplifiers are used and hooked up to this Input. It's Datashet shows no internal connection to "3" the output, nor can i find a connection elswere on the board made to "3". Which input could possibly be on "1" that this makes sense? I do have to miss a connection internally or externally right?

Thanks for having looked in here and thanks in advance for your help.

[texaspyro]

Did you connect your foot to the machine chassis?  Was your foot bare or wearing socks  and/or shoes?   

[radix]

Have a look at page 10 of the datasheet. http://www.ti.com/lit/ds/symlink/tl494.pdf
The amplifier outputs are connected to the PWM comparator.
As for pin 1, I would expect it to be connected to some kind of a feedback network. This would be compared to your reference input (the PWM or DC voltage).

[Detzi]

Just for the sake of completeness.
If someone ever wants to know more, have a look here:
https://www.digikey.com/schemeit/project/k40-lps-7S9UFV0201F0/

@radix:
Thank you! Somehow i did not notice your post untill now. If i had, it would have helped me a lot, and it is the solution!