Solved! Weird USB cable behavior on external drives

[Jimminy]

I have some small 2.5" external hard drives 500GB and 1 TB in usb3 cases. The cases have a microB connector and a short (1 ft) cable ending with an A Male. They work perfectly connected to a usb 3 extension cable (3 or 4.5 ft) from my rear usb ports.

If I use a similar USB 2 extension cable (keeping the same short USB 3 cable as well), they won't work on either USB 3 or USB 2 ports. I thought USB was backward compatible and expected them to simply run at usb 2 speed. Instead, they just make a ticking sound. Tried several cables too.

They do work if I plug the short (1ft) cable directly into a usb 2 port and leave it dangling in the air.

Temporarily inserting a voltmeter shows the voltage close to 5V and current only .2 amps or less.

Oddly enough, I don't see this problem with an SSD with a usb3 adapter, which also uses a similar short USB 3 micro B to type A male. I must be missing something simple, but I can't figure it out.

 

[Insert_Nickname]

If I use a similar USB 2 extension cable (keeping the same short USB 3 cable as well), they won't work on either USB 3 or USB 2 ports. I thought USB was backward compatible and expected them to simply run at usb 2 speed. Instead, they just make a ticking sound. Tried several cables too.

I've had similar issues with certain drives.

Depending on drive/case/cable they might not be able to pull enough startup current via the USB2 cable. That'd certainly result in the clicking you're describing.

Most 2.5" HDD require a whole Ampere (1A/1000mA, though often less in practice) startup current, which are possible on some USB2 port/cable combinations, but not others. Remember, USB2 is limited to 5V/500mA as per the standard. If a drive needs more then that, it'll depend on how the USB2 port is fused. Most mainboards use 2A fuses for USB2 groups, but some do not. It's a bit easier with USB3, since it can supply 900mA, which is enough for pretty much all drives.

 

[Jimminy]

I've had similar issues with certain drives.

Depending on drive/case/cable they might not be able to pull enough startup current via the USB2 cable. That'd certainly result in the clicking you're describing.

Most 2.5" HDD require a whole Ampere (1A/1000mA, though often less in practice) startup current, which are possible on some USB2 port/cable combinations, but not others. Remember, USB2 is limited to 5V/500mA as per the standard. If a drive needs more then that, it'll depend on how the USB2 port is fused. Most mainboards use 2A fuses for USB2 groups, but some do not. It's a bit easier with USB3, since it can supply 900mA, which is enough for pretty much all drives.

But, it I pug the same drive (with USB2 cable attached) into a known working USB3 port, it still doesn't work.

I'm assuming power is on the same pins for both usb3 and usb2. It's been a while since I looked at the pinouts.

 

[Insert_Nickname]

But, it I pug the same drive (with USB2 cable attached) into a known working USB3 port, it still doesn't work.

Odd. Maybe a flaky connector? Some USB cables also have a bad habit of breaking just behind the plug where it's not really noticeable.

But I'm just guessing.

I'm assuming power is on the same pins for both usb3 and usb2. It's been a while since I looked at the pinouts.

Yup. The extra 5 pins in USB3 are only for data transfer.

 

[Jimminy]

Odd. Maybe a flaky connector? Some USB cables also have a bad habit of breaking just behind the plug where it's not really noticeable.

But I'm just guessing.



Yup. The extra 5 pins in USB3 are only for data transfer.

Thanks nickname, I think you just may be right. Tinkering around, I tried the same setup, but with a usb3 cable plugged into the same usb2 port and it worked fine.

There's something strange about these *&$@ cables. They are nice thick braided cables, appear well made, and were very little used, but I know appearance don't really count. Some electrical parameter is obviously the culprit.

Anyway, thanks for responding; It put me on the right track!