External USB HDD keeps ejecting

[Aapjuh]

Hi,

I have a problem with one of my external hdd's which keeps ejecting between 1sec-5min randomly during data transfer/read and reconnects right after.

i did some testing but i'll explain the situation:
my front-hub has 2x usb-3.0 and 2x usb-regular
1st usb-3.0: everything is fine
2nd usb-3.0: random ejects
1st usb-regular: random ejects
2nd usb-regular: everything is fine

i ran chkdsk 2 times boot/windows everything was fine according to it.
now i figured it was something with the power so i tested my other hdd's on all slots aswell.
i have 4 external hdd's, the 1.5tb is the one causing trouble, the 2tb, 1tb, and 500gb are fine on all slots.

what could be the problem?

Thanks in advance,
Aapjuh

specifications:
Windows 7 Ultimate 64-bit
2x 8gb ram
asus z87-A
nvidia gtx770-2gb
720 Watt PSU

 

[LeonardKonrad]

When did you buy your PC, I mean how old is it?
I think,

2nd usb-3.0: random ejects
1st usb-regular: random ejects​

issue is with those ports. They may wear away.