That is unfortunate. It's the fourth unit that I know of that exhibits that same behavior.
The only parameter that could cause problems would be:
On Kunkin: Multi-machine online mode: Offline/Slave/Host -> Use Offline
The tests you made were thorough enough to me.
Nevertheless, two tests can be made:
During the connection process the software asks Kunkin KP184 for the content of the memory address 0x001 which holds the equipment model number (0x0730 = 1840), Kunkin response should be immediate, the software will wait for 5 seconds. This response is not being received, your logs should show the COM port is being closed after 5 seconds.
Loopback test (tests the PC serial adapter):
Please first debug if the 2 USB serial adapters are working properly. Check your USB to Serial Adapter operation with a loopback connection. Please shunt pins 2 and 3 on your DB9 serial port side and connect your adapter only to your PC USB port. Install some terminal software (Ex: CoolTerm) on Windows 10 (Hyperterminal is no longer part of Windows), run the program, configure to 9600,N81 no flow control, turn off echo, connect, press some test keys and check if you receive the characters back to the screen. This will prove to you that your adapter and drivers are at least working.
Once this works you should try the connection with Kunkin KP184.
Don't forget the DB9 serial cable (null modem cable) should cross pins 2 and 3 like this:
2 TXD -> 3 RXD
3 RXD -> 2 TXD
5 GND -> 5 GND
Baudrate: Start with a conservative 9600 to debug de serial connection, then you can use 115200 with a short cable for lower latency.
On Kunkin: Multi-machine online mode: Offline/Slave/Host -> Use Offline
In case anybody else is having trouble connecting using the recommended Digitus adapter plus null modem cable... Try plugging the adapter directly into the Kunkin without the cable.
I checked the pinout of the cable with meter and confirmed pins 2-3 were crossed and cable was not broken, and did loopback test described above, and everything seemed ok, I could see the activity on both RX and TX, but kunkin did not light up the LED or respond in software.
As soon as I connected adapter directly to kunkin without modem cable (adapter came with 12" usb M-F extension cable), I saw LED light up as i pressed keys in coolterm, and software was finally able to connect.
Since the cable didn't seem damaged should I assume its related to cable length (10ft) over likely ~30awg wire? Here is link for the cable I bought.
https://www.amazon.com/dp/B08T997CNS?ref=ppx_yo2ov_dt_b_product_details&th=1Feel kinda silly since I had the adapter and the kunkin already and waited a week for the cable to arrive to try.....
Kunkin is v7 board and 2303 firmware
-JP
edit:
LOL Just noticed manufacturer name for the cable on Amazon is "guangzhouditedianzikejiyouxiangongsi"
Why do I feel like I'm being trolled?