If you look at that thread I posted from xboxhacker Blackaddr has a very good explanation of the part of the JTAG that if it did do damage, WHAT it would damage:
QUOTE
Even if the JTAG wires did cause damage, it would damage the GPU JTAG port, which would prevent XBR from booting, but would not cause any other permanent damage since the JTAG port on the GPU is not used for normal operation with the original NAND.
So anyone saying their video is getting messed up, or RROD'ing sometime after JTAG, its probably coincidental.
The JTAG circuit and what it relies on is not tied to these other areas people are reporting failures in.
QUOTE(SlickWilly440 @ Mar 25 2010, 05:54 PM)

In case cold solder points cause a failure, it is just a temporary failure right (in case of cold Jtag'ed points)? I'm asking b/c the two solder joints on the wires the connect to the diodes on my 360 are so cold that they are jagged.
Others have told me to leave the joints along, perhaps I should get a second opinion.
Cold solder joint on a JTAG would just cause the JTAG to not work 100% of the time possibly. (Occasional the unit would not boot on power on, or you would get more ring of light weirdness) If you have a Jasper and you are not experiencing this I would not worry about it. If you do and are having this problem, re-solder the connections and see. It won't break anything having cold joints on the JTAG.
If you have a Zephyr, you are going to have trouble sometimes, there are confirmed issues with the Zephyr's on power on, randomly.