This is, I guess, power supply related, so posting it here...
I’ve learned recently that ICs can sometimes appear to work ok, even without a "power" connection – and written it up (with pictures and schematics) here: http://www.gooligum.com.au/blog-section/blogart13
This behavior will be well known to some as "parasitic power", and indeed it's a feature of "1-wire" devices, such as the famous DS18B20 temperature sensor, but it was quite a surprise to me to find a 16-pin ADC chip working with no obvious power supply, and perhaps it isn't well-known to everyone else, so sharing it here...