Key Questions to Ask When Ordering 25 Pin Connector

Spring cleaning, and I'm trying to get power supplies for all my devices with missing power supplies. They're all the typical barrel power connector, and I'm having a dickens of a time trying to figure out the pin/hole diameter.

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I ordered the power supplies I needed based on outside diameter (e.g., 5.5mm in my example below) and was surprised to discover that while the jack fit, the center pin did NOT. How do I prevent this from happening in the future? Do they even make calipers that can get into the hole to measure the pin diameter?

Radio Shack has their little keyring behind the counter with every known tip size, but all they can get from that is which stock number fits on their universal wall wart. Personally, I think that these types of "universal" kits are the worst thing to happen to electronics in, like, FOREVER. Too many parts to misplace and the tip-to-cable connector is almost always proprietary.

If I try to pump them for information about what the outer and inner diameters are, they want to know if I'm happy with my current cellular provider. As you may surmise, I'm not a big fan of trusting my local Radio Shack for electronics guidance.

So...that leaves me with a bunch of power supplies that don't fit their devices, and me a little peeved that I have to deal with RMAs, return shipping, etc., especially when I really don't have a clue how to figure out what to order. That also begs the question about how to ensure that I buy the right jack when designing something that NEEDS wall wart power.

Where do I even start? Anyone have any ideas on how to finding the correct barrel & pin diameters when I don't have specs on the jack? Is it really trial and error? or is there some measurement device that's available to help?

UPDATE: I found it! I knew I had something that looked like that somewhere.

It appears to be the same part as pictured in the manual: each 3.5mm jack is in the same place, and the motherboard header is the same.

Comparison of the bracket side of the part I found against the manual:

Comparison of the motherboard side, showing the key and pin 1 are in the same position

Top-down view

Bracket side, including cable

Motherboard side, including cable

Motherboard connector

With the soldered wires into the external connectors exposed

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Close-up of 3.5mm jack solder points

Close-up of one side of the game port solder points

Close-up of the other side of the game port solder points

Edit: Added photo comparing motherboard side to the provided manual

I thought I had something in my parts bin that looked like the bracket mentioned in the manual, but couldn't find it.

I couldn't find any photos of the part online, either, but it may look something like these:

This is a pretty common 15-pin Game/Joystick/MIDI port used on many motherboards from around that time

Single bracket with separate 25-pin parallel port and 9-pin serial port

Those kinds are the most common, with wires connecting headers on the motherboard to a simple port screwed into a bracket. There are no electronics have any kind in those examples.

However, it's also possible to have a circuit board connected to the bracket, instead of the wires going straight to the port, like this:

There isn't any "logic" on this board (i.e. no microchips), but it has some supporting components to (I'm guessing) help with keeping the signal clean, or provide protection to the motherboard electronics.

Anyway, if you do go the route of testing the pinouts, I'd guess the audio pins are the ones closer to the "Sound Pro" chip, simply because there are 15 pins at the "top" (relative to the orientation of the image in the manual) of the header including the key pin, and the joystick port uses 15 pins. This is purely a guess, but should be reasonably easy to verify (or at least rule out) with a multimeter by seeing if the +5V is available on pin 1 the pin next to the key (16). If that's the case, then depending on whether pin 2 or 14 is also +5V would say the orientation of the joystick pins (assuming the motherboard manufacturer wired it the easy/typical way which is not always the case).

You can see a typical 15-pin joystick header pinout here: https://www.frontx.com/pro/p_030.html

If that works, then you've narrowed down the pins to test to the 10 "below" the key. I'd also guess each of the 3.5mm jacks use three wires, each with L/R/Gnd, so maybe try to find which of those 10 pins have continuity with ground, and that might give some hints to where the left/right signal wires are for each. I'd only tap the probes very briefly on each pin if doing a continuity test, since technically the multimeter sends some power down a probe to see if it (and how much) returns on the other. But I don't think any damage would come from doing that kind of test, since they're connected to something directly exposed to the outside and are typically better-protected than headers designed for use completely within the chassis.

Anyway, sorry, it's not the answer you were looking for, and you may have thought about all these things already, but that's where I would start if I had that board.

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