Loose cable tale

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mathog
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Posts: 108
Joined: Thu Dec 15, 2016 5:22 pm
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Loose cable tale

Post by mathog » Sun Jan 24, 2021 4:18 am

Around six months ago our DVR died and was rebuilt with a new motherboard and power supply. The last month on two occasions it locked up briefly but on reboot there were no errors or warnings during the boot. Finally yesterday it did it a 3rd time and on that reboot there were all sorts of /dev/sdb errors. On closer inspection there were a ton of CRC errors, and that in turn suggested a loose cable. So this morning I took it apart, and lo and behold, the SATA cable for that disk was angled up something like 15-20 degrees where it plugged into the motherboard. I have been working on computers for a long long time and have never seen an internal connection do that on a 6 month time scale. As near as I can tell the coiled SATA cable had just enough spring in it to apply a tiny amount of force to the end of the cable, and over quite a long time it was enough to tilt the cable out. The disk end was in square. The motherboard end is now zip tied to a bit of the case about 2" up, so hopefully it won't do that again. Yes, I know there are latching SATA cables, but up to now I have never needed one. This machine wasn't seeing a significant amount of vibration or movement - it was just sitting on a shelf for that entire time.

Just to be thorough the long SMART test was run on both disks. They were both healthy, although the problem one now has a UDMA_CRC_Error_Count of 51.

mathog
Senior
Posts: 108
Joined: Thu Dec 15, 2016 5:22 pm
United States of America

Re: Loose cable tale

Post by mathog » Tue Jun 01, 2021 4:10 am

Even the zip ties did not stabilize that connection, the cable pulled up again. Both disk cables were replaced this weekend with latching SATA cables.

I think the root of this problem for non-latching cables is that they enter the compartment where the motherboard is through a small hole which is about 1.5 inches up and over from the SATA connectors, and the cable comes in exactly parallel to the bar in the middle of those SATA connectors. So with the sharp turn on the cable too much tension remains and it pulls up from the far end of the motherboard connector. There isn't space in the case to loop the cable around much to take the tension off. The previous motherboard had connectors further away from that hole and with the SATA "bar" perpendicular to their path, so the cables there bent more naturally and never pulled off. In the current motherboard the SATA connectors are very close to one corner and are turned the wrong way to work well in this case.

I sure hope the latching cables work and never have to come off because one of them has the latch release close to and facing a case partition. It will be tricky to unhook it if the need ever arises.

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