Re: FireWire device burning

[Allan D. <al...@fa...>]

On 10/04/15 05:35, Ларионов Даниил wrote:
> Hello Stefan.
>
> You seem to know a lot about IEEE1394 hardware, not only software. Could you please tell me whether it is possible to burn a FireWire device by not connecting its housing to the host's?
> I have a ScanControl surface analyzer from MicroEpsilon. It is essentially a DCAM camera with IEEE1394 interface.
> I soldered my own cable, because I needed a special one (not fracturing at extremely low temperatures etc.) Since the scanner has a separate power port, I soldered only 4 wires (TPA+, TPB+, TPA-, TPB-).
> I also connected the connector ground to the cable shield at only one end of the wire. I asked the manufacturer employee and he said that's ok.
> The scanner worked fine for a while, but then it just suddenly broke. I sent it back to the manufacturer and they sent me these photos:
>
> https://yadi.sk/d/nlIi62iXf9dEE
>
> and recommended to buy their own cable. I did that, and it seems that the only difference between my cable and theirs (besides the absence of power wires) was that the shield was connected to the connectors at both ends.
> Did you have similar cases in your experience?
> Thanks in advance.
>

Contrary to the advice you got, the earth/shield coonection to both ends 
is critically important - without it the device at each end can float to 
large relative voltages, well beyond the Common Mode voltage range of 
the input electronics.  You are lucky it only killed the analyzer.  If 
both devices have explicit, and common, ground connections then only one 
end need be shielded, and not having either end connected may also work 
fine.  Most plug-pack power sources have floating outputs.