Tether Nikon D70 to l iPad and use as viewfinder for the Nikon

No, you shouldn't. The D70 works as SLRs have worked for half a century, allowing you to compose your photos through the viewfinder. The ability to use a dSLR as a point-n-shoot camera, wobbling at the end of your arms, is a relatively recent development. Nikon introduced it into their lineup with the D3 and D300, released years after the D70.

You need the Camera Control Pro software from Nikon in order to use the D70s from the PC in tethered mode. You can download a free trial version of CCP from
http://support.nikontech.com/app/answers/detail/a_id/61

I have had "dark pictures" from each of my Nikon DSLR (D70, D80, D200, D300) cameras usually when taking pictures from a tripod and/or the self timer. Situations where you take your eye away from the viewfinder which allows stray light to enter thru the viewfinder and throw the auto exposure way off. Not sure if this is what is happening to you.

buy a Canon

Check here: NikonUSA

The error code "CHA" is telling you that the CF card you are using for storage is not compatible with the camera. You should consider trying a different card, perhaps a slightly older one that is not as fast.

I use a SanDisk Ultra II card, and that works fine for me.

That depends on the parts needed. What are you looking for?

You can try B+H photo for the every day parts (cards, viewfinders, etc.). Or if the parts are the internal and finer things, you'll have to go to Nikon repair specialists.

These lines are normal. See the last paragraph on page 8 of the D70 manual.

Make sure your memory card is OK. Take it out, put it back in or try another card. Be sure battery is charged. Should not see low battery sign in viewfinder or in top panel. Try a reset. There is a problem sort of related to what you describe where a firmware update may cure it. D70 Firmware Update 1.0.1 / 1.0.2 - Windows. One of the problems this firmware fixes is :"When images were captured in Continuous mode at an Image size setting of M and an Image quality setting of FINE, the memory card access lamp sometimes glowed continuously and the camera could not be turned off with the power switch. This problem has been corrected." This bit of advice comes from another Web forum, not my own discovery. Maybe this happened and ran down your battery, unbeknownst to you. Turn the camera off and power it from an electrical outlet. Update the firmware per instructions on the Nikon site. If this does not work or if your firmware is updated, call Nikon for further advice. You may need to have it serviced. This blinking light problem has been mentioned on PN and another forum. Nikon may be familiar with it already.

It's perfectly normal as described in the manual on the bottom of page 8.