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Converting an Intellicall payphone to a regular home phone

Started by MaximRecoil, March 23, 2024, 11:01:09 AM

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MaximRecoil

About a dozen years ago I made a thread here where I talked about wanting to do this, but I didn't know enough about how Touch-Tone keypads worked at the time to actually do it:

https://www.classicrotaryphones.com/forum/index.php?topic=7423

The payphone's chassis is an Intellicall 3003 (which has never worked at all for as long as I've owned it) and the housing is a Tidel-3. The keypad is stock and it doesn't have the tone-generating hardware built into it, so that stuff must be on the Intellicall chassis.

In order to convert it to a regular home phone using 2500 type components, I needed to know the pinout of the keypad and I needed tone-generating hardware.

I'm already familiar with the newer types of 2500 keypads that use a 16-pin tone-generating chip (e.g., TCM5087, S2559FS, UM9559E, and maybe others that work the same way as those three) in combination with a 3.58 MHz crystal so that's what I wanted to use. They are simple and I can easily fix anything that could ever go wrong with them, unlike the convoluted older designs (like the Western Electric type 35 keypad).

So I bought one of those newer types of 2500 keypads, an NOS one on eBay for $10 which uses a UM9559E chip in order to use its tone-generating PCB.

I used a continuity meter to figure out the pinout of the Intellicall's keypad (see attached picture number 3), and once I did that, all I needed to do was wire the 7 relevant pins on the Intellicall's keypad to the 7 through-holes on the 2500 keypad's tone-generating PCB (see attached picture number 4).

Attached pictures 1 and 2 show a complete phone wired together, using the Intellicall's keypad, the eBay 2500 keypad's tone-generating PCB, and an ITT 427 type network, and everything works perfectly.

To connect wires to the Intellicall keypad's header pins I used some front panel connectors (which already had wires attached to them) that are intended for use with a PC, since they are the same size and pitch as the front panel header pins on a PC's motherboard. I used a pair of 2-position ones for pins 1-4 (I couldn't find a 4-position one in my junk pile), and a 3-position one for pins 5-7.

The only thing I need to do now is come up with a way to mount the tone-generating PCB, the network, and the ringer in the payphone's upper housing. I'll probably screw in a wooden board below the keypad using the 4 screw holes that are already there, then screw the tone-generating PCB, the network, and the ringer to the wood. I'll need to make a little metal bracket with a hole and rubber grommet, and screw that to the wood, for the rear mounting stud on the C4-type ringer to slide into.

MaximRecoil

I don't have quite enough room to install a C4 type ringer in the upper housing, so for now I set out to find the two header pins on the keypad that go to the built-in Murata brand "ringer." I couldn't use a meter to find them because I can't access the other side of the keypad's PCB without breaking the melted-over plastic posts that hold it in place, so I used trial and error.

I was hoping they would be two pins that were side by side, otherwise it could have taken forever to find them. As luck would have it, they were side by side, and polarity doesn't seem to matter; it makes the same "ringing" sound either way.

5415551212


MaximRecoil

Quote from: 5415551212 on March 24, 2024, 10:00:48 PMVery cool project, thanks for sharing.

Thanks.

I made a bracket out of sheet metal to mount the tone-generating PCB and the network to. I attached the bracket to the upper housing with 4 machine screws that were already there, so I didn't have to make any modifications to the payphone. For that matter, I haven't made any actual modifications to the payphone at all, nor do I intend to, so this conversion is completely reversible.

I also ditched the annoying ITT network and replaced it with a Western Electric 425 network, which I like a lot better because it's potted and has nice screw terminals. The ITT network's tightly packed QD terminals are a pain when it comes to inserting and removing the spades, because other already-connected spades get in the way of your fingers. A lot of times I have to use tweezers.

A lot of the current wiring that I did is temporary. I ordered some 22-gauge wire (the biggest gauge you can use with typical phone spades and DuPont connectors) and when it arrives I'm going to replace all the wiring and connectors from the hookswitch, "ringer," and keypad-to-tone-generating-PCB. I like bigger gauge wires even when the amperage of the circuits isn't enough to require them, just for the sake of durability (less likely to break right at the connector when doing wiring). When I'm done the wiring will look neater too.