Katie, I just heard from the man who repairs the Ilford 500, he is ok for me to give you his email. His name is Desmond Wilson. He will be able to help you, if you canot fix it by swaping around. I'll PM his email, so that bots don't harvest it from the forum.
Indeed, you should switch out each component at a time, until you find the faulty one. Glad you have spares, I should think of that.