I bought a RJ11 6P4C cable from a local store at $10 (i.e. around 1.3 USD), I've prepared to modify the pin layout cutting one end off, re-arranging the cables and by crimping another RJ11 there.
To my surprise, the cable has identical layout with the iOptron cable! Therefore, no hacking has to be done.
And on plugging in, everything work flawlessly, no more problem! Yeah! I saved a lot of money and a lot of trouble! Solar imaging could be resumed shortly.
The "GPS ON" sign on the LCD display disappeared, and the mount changed itself to EQ mode and cannot be changed back to alt-az mode. There will be an error message saying that the controller cannot communicate with the DEC motor.
Faulty hand controller cable.
Pictures are much better for the illustration. First of all, examine the original cable which looks like this. Check the color of the cables inside the jacks of both side. You will see that they are in the following sequence as shown. Both sides are identical in layout and by using a multimeter, you will know that there are just four parallel cables inside without any cross-over, we can it a straight cable technically.
The jack is just similar to those for telephone. However, some telephone system has cross over cables, that means, the pin layout of the jacks are not the same. We will need to find those which has two identical layout on both jacks.
Luckily, I found such a cable locally from a store at a very low price, less than 1/10th of the original one. Of course, it you cannot find such a cable, you can always hack one by yourself. Simply buy any telephone cable, cut one ends off, and buy a new RJ11 jack and re-arrange the pin layout with a crimpler tool.
After replacing the cable, my Cube works again flawlessly.