I think your electrolysis technique is a bit flawed. Why would you wrap the boards with aluminum foil? That will just get eaten by the HCl. Motherboards also contain alot more than just gold, (lead, ruthenium, platinum, copper, zinc, palladium, tin, etc) all of which will readily dissolve in HCl, and the amount of gold in each board is negligible- you probably paid more for the quantity of HCl.
I take it you are trying out the Wholwill process of purification? It only works if Gold is the only soluable metal salt in the mix. Ideally, your gold should be deposited directly on the cathode, and shouldn't not precipitate out. The money bet is on the yellow precipitate being a mix of Aluminum Chloride and Iron Chloride and God-knows-what-else Chloride you pulled off that board.
There are a few guides online as to how to extract metals from boards that are easier and cheaper. Here's one that shows what components contain what metals, so you can take out just what you need and not bother with 95% useless bulk. http://www.goldnscrap.com/index.php?option=com_content&view=article&id=49:recovering-gold-and-precious-metals-from-circuit-boards&catid=34:scrap-circuit-boards&Itemid=27
Good luck and have fun!