I have a Genie garage door opener Model 409 that I'm sure is ancient, but in good working order. The remote is not. I have purchased a replacement and set the dip switches accordingly, but no luck opening the door. Advice (via long distance phone call with brother) was that the frequncy of the new opener may not be the same. Any idea how I can figure the frequency? I do not have an owner's manual and (surprisingly) am not finding much help on the internet.

Or, any other ideas of what may be wrong?