How to connect a GSV-2 with RS232 to a USB adapter?

the assignment of the 6-pin terminal strip for the RS232 connection is this:

Many device versions have a 5-pin terminal a-E, some older ones only have 3-pin, the allocation to the RS232 lines A-B-C is the same for these too. Only these 3 lines are to be wired, leave out the other 6 of the 9-pin Sub-D connection.
The designations RX and TX are given from the point of view of the GSV-2, i.e. it transmits at TX and receives at RX.

If the USB adapter has an RS232 connector with pins, which is very likely, you don't need a zero-mode exchanger ("gender changer" or similar), but you simply assign it as follows:
Pin 2 to C
Pin 3 to B
Pin 5 to A

If the USB adapter has a socket (which is very rare), this is probably a null modem connection, then you have to swap RX and TX.

If that doesn't work, I ask you to consider whether it could be that your GSV-2 was previously reconfigured by someone and the communication bit rate, i.e. the baud rate, was changed. This is sometimes done in order to be able to set higher measurement data frequencies. A configuration jumper must be set to change the baud rate in the device.
It is therefore easiest (as soon as you know that the connections are wired correctly) to try out the baud rate in the GSVmulti program. GSVmulti first suggests the standard baud rate of 38400 bits/s, you can then select higher ones as a test, e.g. 57600 or 115200 etc., here "bits/s" in the middle:

In rare cases, the baud rate is also reduced, e.g. with very long connection cables or when old devices are connected that can only use slower baud rates.