I converted an old broken payphone to a regular phone
It's an Intellicall 3003 chassis in a Tidel-3 housing; not exactly desirable as far as payphones go, and it's been dead as a doornail for as long as I've owned it (2008). Even if I were to fix whatever is wrong with the chassis, it would be pointless to do so, because programming software for it is made out of pure, 100%, grade A Unobtanium. Plus I already have a fully functional payphone; a Western Electric 1C, which is the original (they invented the iconic single-slot payphone design in the mid 1960s that companies like Protel, Nortel, Elcotel, GTE, and Intellicall copied starting in the 1980s).
I've wanted to convert it to a regular phone ever since I got it in 2008, but I never knew the pinout of its Touch-Tone keypad, and technical information about Intellicall payphones is just as hard to find as programming software.
So yesterday I decided to sit down with a continuity meter and figure it out. Surprisingly, it didn't take very long, and once I had the 7 pins (out of 20) for the keypad matrix identified, I wired them to the tone-generating PCB of a keypad from a typical 2500-type desk phone, which I in turn wired to an ITT 427-type network, also from a 2500. At that point it was a working phone that I could dial from the payphone's keypad:
https://i.imgur.com/Etke4aK.jpeg
https://i.imgur.com/xByBYL3.jpeg
However, it was still using the 2500's hookswitch assembly, and I needed to wire it to use the payphone's hookswitch. The problem was that a 2500 uses 3 switches at the same time (one to open or close L1, one to open or close L2, and one to open or close the receiver shunt) and the payphone's hookswitch only has one SPST microswitch.
I decided to put the payphone's hookswitch only on L1, which is all that's necessary for functionality (switching L2 is redundant, and the receiver shunt switch just minimizes the pop you hear when you pick up the handset). That worked, but it worked backwards, i.e., when you hung up you got a dial tone, and when you picked up it hung up. Fortunately, the microswitch could be wired as normally-open or normally-closed, so that was an easy fix.
Then I needed to figure out the pins that connected to the built-in "ringer." It would have been easy if I could have seen the other side of the payphone keypad's PCB, but there was no way to do that without breaking the melted-over plastic posts that held it in place. Trial and error was the only way, but it only took about 5 minutes to find the right 2 pins, so now its "ringer" (more like a "chirper") works too.
The only thing left to do is permanently mount the tone-generating PCB and network into the payphone's upper housing. I'm still thinking about the best way to do that.
Edit: I forgot to include a picture of the whole payphone. It weighs about 50 pounds:
https://i.imgur.com/QHVQ5I8.png