I recently acquired a circa 1972 2500D series desk phone that I would love to make work with my Obi200. I get a dial tone when I hook up the phone. However, the dial tones for 1, 4, 7 don't seem to work correctly (they're very faint but don't break the dial tone). 3, 6, 9 sound fine. 2, 5, 8, 0 are somewhere in between.
I did some Googling and looked into the polarity issue, switching L1 and L2, but I received absolutely no dial tone then. Further, the phone isn't ringing when I call. I found a post elsewhere in this forum suggesting changing the ring voltage to 82VAC in expert settings, but the phone still didn't ring. I also tried to switch the pin position for the ringer inside the phone to no avail.
So far I haven't been able to make this phone work at all. I know I can use a more modern phone or get a cheap replica of the 2500 series phone on Amazon, but I really want to put this vintage phone to use! Has anyone had any luck getting their older 2500 series phone to work with the Obi200? I've included a photo of the phone and the wiring board inside.