Hi
I want to replace the multi-turn pot on the circuit board with a volume resistor for easier control of the output voltage, but when I do so, the IC starts heating and the output voltage is almost the same as the input voltage, and when I solder the original pot back in place it starts working again, what is the issue here and how do I solve it?

 

Maybe there is no connection between the output and IC pin 5. Check the resistance between the wires of the replacement control before fitting it.

 

Explain what you mean by a “volume resistor.”

 

Is your 'volume resistor' also 10k Ohms ?
How long are the wires from that control to the board ?

 

Hi,.
One possibility is that the PCB is double-sided, and not PTH for the components, and the TS is just soldering to one track side.
E

 

A “volume” resistor usually has a log taper.
Use a pot with linear taper.

 

It seems likely that the TS has not measured the value of the resistor. And it is even more likely that the actual connection is not quite like the original circuit.
In addition, this is a switch-mode supply and probably lead dress matters quite a bit.