I own 2 fx-7400gii, but the problem is, that none of them works.
Both show only a blank screen with "OSUpdate" when booting, i DO NOT mean the bootcode os updater ("OS Error Please Update OS"), but i can still invoke it on both of them.
The OS on the first calc does not seem to be touched: When I press any key except F5, / (division), - or EXE, it boots to the main menu, in which I can navigate, but there has to be pressed one key all the time at least (I can change the key), if there is no key pressed, it returns to OSUpdate. Every key works, except the said ones, so I sadly can't reset the calc (I have to press F5 to do so). If I turn the calc off (The calc writes changes to the Flash memory when turned off, correct me if I am wrong) and on again, the main menu shows up (I dont have to press any key), but it is completely frozen at the point where I turned it off. I remember that the first time the Error occured whas when I shorted one of the points on the back with a pencil, so I thought there could be still a connection because of some graphite which is still there, so the pin is shorted the whole time, but it doesn't seem so (checked it with a multimeter). I also have a communication cable from 3-Pin to PC (I took an USB to 5V RS232 TTL cable and connected TX to RX, RX to TX and GND to GND, bought it from amazon and it works perfectly with FA-124 and fxRemote). The problem is, when I tried to dump a flash image, it seems to work (it reads the data and shows the speed, its around 5 kbps), but at the end of the process it says "Filesize of the written image NOT OK", and whenever I try to restore it, the process stucks at "FXCheckImage C:\...(the path)". I also thougt of getting the source code, cutting out the FXCheckImage command (i know a little C/C++/C#), and recompiling, but I cant find the source code of fxremote. Surprisingly dumping the flash seems to work with the "broken" calculator, but it leads to the same result (Filesize of the written Image NOT OK). By the way, the OS version is 02.02.0701.
The second calc also shows OSUpdate, but here I just cant access the main menu, there seems to be no other option than this OSUpdate seem, so I guess the OS is completely deleted here.
I would be very glad if someone here could send me a fx-7400gii OS dump or tell me how to dump it without getting that error. If I forgot something, please tell me, I can give you the information, and by the way I am german and my english is not that good, so sorry for it.