SOLVED! $0 DIY Nikon D70 CHA/CHR Error Fix FREE*

Symptoms: 

You love your D70 but it keeps giving an error on the top screen, "CHA" and every once in a while you lose a picture.  The camera will say "This Card Cannot Be Used" with a known-good CF card, or when it does work, it will sometimes say "Zoom Cannot Be Used With This File" or it will fail to record an image.  Sometimes it even says the card has to be formatted - which deletes ALL your photographs!

This rarely happened, then it got worse and more-frequent.  The camera is no longer a beloved friend, it is become an enemy and not to be trusted.  Maybe you even (ugh!) resorted to using your phone's camera instead, because at least it reliably captures images, however low-quality they may be.

You have found that pressing harder on the CF card in the camera, or maybe a few insert/removes of the card will temporarily clear the error, sometimes for weeks!  Perhaps you have taken to leaving the card in-camera and using the much-slower USB interface on the camera instead when downloading files.

Solutions:  

For money: The CF slot in the camera is bad. It is about a $40 part if you can find it, and the repair requires disassembly of the camera.  Having a shop repair the camera might be more expensive than buying another, newer-model, used body.  But.  I have not seen the CHA error in months and I am happy to consider this fixed, "free."

Free: 
*Tools required: 

• Ability to do fine-pitch soldering by hand
• Helping Hands (with magnifying glass!) 
• Veeeery fine-tipped soldering iron 
• Very thin solder

Very carefully disassemble the D70 to the point where the CF slot subassembly/circuit board is completely free of the camera.  Use your helping hands to hold the board while you work.  Very quickly and gently reflow ALL the solder joints between the CF card reader slot pins and the circuit board.  Add just a tiny daub of solder to each joint.  Make this a very quick operation to avoid melting the plastic pin frame and make it a tiny bit of solder you dab on there to prevent bridging/shorting between adjacent pins.  Thoroughly clean all flux residues when you are done.  VERY CAREFULLY inspect your work for solder bridges, as you could kill the camera by doing this wrong.

The REAL root cause: These were machine-soldered with either the wrong sort or not enough solder, or they did it wrong>  The joints ended up "cold" from the factory.  Over time, with each insert/removal of your compact flash memory cards, the solder joints are stressed and eventually they break.  This is a problem of execution, not design, and Nikon would repair it under warranty when a warranty still existed on this camera.  These days, you will pay handsomely for them to repair it if they still will, but at least it will be returned VERY clean!

What is not the problem: Your new cards and your old cards are probably fine if they will work in your computer's card reader.  You DO NOT need to FORMAT your card and lose all your vacation photos!  An image-recovery software tool should be able to extract any images properly written on the card, even if the camera cannot read them!  The pins are not plated with too-thin gold plating, which eventually wore off.  Some people (me included!) found partial success coating the pins with dielectric grease because it lubricated the pins, putting less mechanical stress on the bad solder joints with each card insert/remove.  The phase of the moon is not incorrect. 

At least in my case this was a fairly straightforward repair of a problem common to poorly-made soldered electronics. 

MANY thanks to ifixit.com for their wonderful disassembly/repair instructions!