Sangamo type L movement

by Burt
(Kansas)

I have a Sangamo clock that I can't get the 1/2 hour strike adjusted properly. I have read that this is tricky if you don't have the right tools and know-how. It strikes once (one striker only, which is correct) but then it strikes the other hammer a few minutes later. Can anyone help me with this adjustment??

Thanks,
Burt
bmannell@embarqmail.com