Hi Greg,
Welcome to the forum. The internal reference defaults to off at power up according to the datasheet. I will go ahead and get a hold of the ADS7828EVM and confirm this on the bench, this may take a couple of days.
Is the scope shot above taken right after power up? How often does this behavior occur and under what conditions? If possible, can you please post an schematic of the circuit, including the external 5V reference and all the devices connected to the REFIO pin?
Thank you and Best Regards,
Luis
