Optical Sensor installed in Qanba Q4 Fightstick

A hobby of mine is to use small arcade style controllers to play fighting games. I'm pretty decent. Anyways, I recently found that an optical sensor existed that could replace the microswitches in the joystick. The microswitches act as a mechanical sensor that detects movement on the joystick (up, down, left, right, and the corner combinations). These are all well and good, but having a silent joystick that is slightly more precise is more my style. The only complication is that the special optical sensor required a power source and while I could have soldered something directly to the circuity inside my Qanba Q4, I wanted the option to switch between the optical sensors and the microswitches without having to solder and unsolder every time between the two.

So I designed a little pcb that would facilitate as a USB to power hub. The intention was to make the cord modular from the fightstick so instead of having an always connected power cable, the cable could be removed completely. Also, the power for the Qanba pcb and the optical sensor would connect to my pcb and could be disconnected when switching from optical to microswitches.

So this is the board. Super small, super simple. Sadly, I was not able to use it. Not because it didn't work, but because I did not have the proper connectors to attach to the Qanba pcb. Dupont cables didn't work, molex didn't work, and the do-it-yourself wire connectors that are in the instrument room here at Purdue didn't work either.

I'm under the impression that the wire connectors that Qanba uses are special or at the very least not very common. While iteration ALPHA didn't work, I plan to go back with iteration BETA to hopefully use my design, but because I wanted to use the sensor last night I had to improvise.

I'm not sure if anyone knows the name for these particular connectors, but if you do please email me because I don't know what to search for.

Also because I was really annoyed that every photo of the Qanba Q4 pcb was taken by a potato, here is a better photo of it with no modifications and I've unhooked the microswitches along with the power connector from the USB cable.

Here is my improvised cable soldering. I was really hoping to avoid soldering so that I could keep it simple for others to implement, but c'est la vie.

It's kind of a bad photo, but the main points to take from it is that I'm pulling 5 volts (red) and ground (black) from the USB power cable. The other four colors are direction inputs for the Qanba pcb.

So here is the final connection scheme. I recycled the Sanwa microswitch cable that was already being used with my JLF stick (the joystick itself) for the directional inputs, and the important part is that you can see that the power and ground connectors are soldered to the USB power cable.

Everything worked out a lot better than expected after I already gave up on finding a proper connector at 11:30 pm. Minimal soldering and the optical sensor works very well. I don't expect there to be any questions, but if you're looking at this in the future four years from the date of this post or something like that, feel free to send me an email. I'll probably respond unless the internet stops being a thing in the future.

HP 3310A Disassembled and Potentiometer Repair

I originally wasn't going to make a post about fixing a potentiometer on the HP 3310A function generator because I thought it should have been relatively easy to replace/repair a simple potentiometer and wouldn't really have a lot more content to add to what I already did. Holy Packard was I so wrong. More like semi-wrong. Repairing the potentiometer was relatively easy as expected, but all the disassembling to get to it so I could even work on it was just incredible. I know in the last post I said the same thing, but friggin' kudos to HP for making a solid box of interlocking, military grade spec parts that is just an incredible pain to take apart. A majority of the photos that I took were not initially for a blog post, but rather documenting how to get this contraption back together once I realized that this was going to be a lot more extensive than unscrewing a few parts.

In the last post about the 3310A, I kind of went over a little of the first bit on how to start taking this thing apart so this is sort of going to pick up from there in the breakdown process.

The potentiometer that is used to vary the amplitude of the function generator was really erratic every time it was adjusted which suggested that the wiper contact was all gunked up with all sorts of gross just from use over time. So the initial idea here was to just replace it, but first I had get to it. Due to how the function generator was constructed, it was necessary to take it almost completely apart.

This is the side panel that screws down each of the printed circuit boards to the box itself so that it's nice and secure. Naturally, each set of screws are different sizes and have specific placements so this photo was a lot more useful to me once I had to put it back together.




But what's this? It only takes off the metal frame, but at least now we can see the board that has the potentiometer on it.

Getting the board out itself was not necessarily professional, but once the metal side frame is removed you can flex the box to wiggle out the circuit board.

Here are more photos of the board in question once it had been wiggled free. There are two other circuit boards that interface with it, one of which needs to be removed completely to get our potentiometer free.

Now that I can get a good look at the potentiometer, I figured that it might be worth a shot to see if cleaning the wiper track might solve the issue... but this only became an option after finding that the instrument room did not have potentiometers with the proper physical dimensions.

So prying back the clamps on the dust cover plate revealed this was kind of a unique potentiometer. Rather than having a single contact tooth, this potentiometer had contact teeth so to speak. The photo shows a comparison of these two kinds of potentiometer contacts.

Anyways, just from many years of use the contact teeth made tracks in the resistive strip sort of causing an eroded mess of shavings. I am not certain, but I am under the impression that the resistive strip shavings were preventing a good electrical connection. Cleaning up the tracks with ethanol worked out nicely.

Before reassembling everything, it was suggested to me by Dave Azpell that a tiny hole should be drilled in the back of the dust cover. If the potentiometer started misbehaving again ethanol could be easily applied without having to take the whole thing apart again.

 

  Here it is mostly put back together with a little video showing the output of the function generator on an oscilloscope while I adjust the amplitude with the newly cleaned potentiometer. 

EDIT (9/17/2015): Someone emailed me about getting some scans from the service manual. So here are the two sets of scans I did. I did a very basic one that included the board layouts. The second one focused on the A1 board that has the triangle amplifier and +/-5V detector.

Here's the link to my Google Drive