i bought this soldering station from the USA and it is 110 V. I need it to be 220 V. Is this possible without external tools?
There are 3 Trimpots: V1 VR1 VR2
This is the inside of the station:
First check the specs of the unit using its manual. Many devices (such as phone chargers) accept a large range of voltages so that they may be used all over the world, this station may be the same.
Alternatively, you could find a step down converter that will convert the 220 VAC to 110/120 VAC (something like this: https://www.amazon.ca/Voltage-Converter-220-240-110/dp/B001ES8YY6). Just want to note that simply using an adapter would not be enough because the source voltage would still be 220 VAC.
The power appears to be derived from a switching power supply based on a Power Integrations TOP253.
If the power supply has been designed for 80-265VAC operation, it will probably work as-is (except for the plug). It could have been designed as a doubler feeding the supply, but it does not appear to be so designed.
So, refer to the manual and markings on the unit for the recommended voltage range. If you are outside of that, the effort to make it compatible internally would not be worth it.
My impression is that it probably does not have valid safety agency approvals for Western countries- looks like a somewhat shoddy Asian product.
The controller looks as if it's an SMPS convertor. The input looks to have a simple bridge rectifier and 2 supply caps. The input voltage limitations could probably be gauged by looking at the voltage rating of those caps.
It has a transformer, and given the size the unit may be switching in the kHz range.
Unless the unit is marked to accept 110-240V as a range it is unlikely you will find any way to alter the input voltage range based on the pots in it.