Before converting, generate a SHA-1 hash of the CHD. After converting to ISO, disable compression (rebuild an uncompressed CHD from the ISO) and compare hashes.
Here is an advanced that processes CHDs in parallel: convert chd to iso better
Then, after conversion, use a tool like Cygwin or Get-FileHash (PowerShell) to compare the ISO to the original source disc's known hash (if available from Redump.org). Before converting, generate a SHA-1 hash of the CHD
A: Never use online converters for ROMs/ISOs. They are slow, insecure, and often cap file sizes at 500MB. Always use local software. convert chd to iso better