Fuse Change in HP33120A Function Generator

Simple post. Most of the function generators that we have here are fitted with a fuse holder that allows us to quickly swap out busted fuses. This one in particular however is not.

Changing the fuse in this one is about just as simple except you have to take it apart before you can change it out. I just thought it would be neat to show the guts of the function generator.

The photo below and to the left is just the new fuse in the sockets. It looks like a goofy looking resistor.

The photo to the right is measuring the resistance of the old busted fuse. It's measuring 6-ish Megaohms which doesn't make for a very good fuse.

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

Cuphones - Cup Headphones?

Today was kind of interesting for simple side projects. Mark Oscai, a student I work with and regular lab wrecker (just kidding), came in today with something that he had seen in class. I guess one of the ECE 311(Electric and Magnetic Field class) professor, Professor Melloch, did an interesting show and tell with copper wire, magnet, and cup. It would seem Professor Melloch makes a really simple speaker using these things to show how fields work, but I can't really say for sure because my experience with ECE 311 was super boring. Granted, I'm a physics minor and took a more interesting version of the class through the physics department (Phys 330). And by interesting I mean really, really hard. I still had to take ECE 311, but compared to the physics department equivalent it was a breeze.

Anyways, enough boring stuff, here are some of the photos of the materials that were used and just photos as Mark constructed the cup speakers.

As you might expect, the sound wasn't that great so I got the bright idea to add water inside the cup to see if it would dampen some of the noisiness out. The water kind of acted like a low pass filter in the sense that it did in fact dampen the noise, but it also dampened everything except for the muffled bass. It sounded as if you were sitting in the auditorium restroom during a concert. It was pretty interesting.

Here is Mark messing with his magnets and coils to make his speaker work. Mark however is kind of an interesting bird and even though he was able to recreate the speaker working, he still wanted to add some of that Oscai flair to it, which leads us to his revision two of the speaker... or rather... cup headphones.

And just in case you're skeptical of whether or not it works, I have a short video of the device working prior to Mark's... creative headphone revision :)

Sorry about all the background chatter. There were a lot of people really interested in this fun little project. Also, I am sorry once again for vertical videos. I'm not really the best photographer.

Instrument Room Side Projects

A couple of students I work with in the instrument room here at Purdue also have some side projects that they get involved with. Some are just looking for extra experience in soldering and others are just helping out friends.

First up is Travis Garza, I helped oversee his progress to make an FM wireless microphone because he wanted some extra soldering experience. What a go-getter sophomore. All I did was help him learn good soldering techniques, but he did all of this handiwork and I am proud of him even though we weren't able to get it to work.

Second up is Kyle Woodworth, I was not even involved for this project but managed to see his handiwork just as he finished so I only have a few photos at the tail end. One of his friends asked if he could do a fixer-upper for his Gamecube controllers. (I guess his friend is really involved with Super Smash Bros.) According to Kyle, which didn't take photos of his progress, this controller was 80% nasty and 20% super gross so I'm impressed with his cleaning and re-soldering. Allegedly, the capacitive coupling can be reduced thus increasing the response time for these controllers according to Todd Wild (my overseer, in Todd we trust).

 

Repairing HP 3310A Function Generator

It is not uncommon that lab TA's report that their lab equipment is broken in some way or another. Usually it's some trivial thing like they forgot to check if it's properly powered or didn't know how to check if the fuse is blown, but from time to time the equipment is in need of some serious maintenance.

So this was brought into the back and the TA just mentioned that he couldn't get it to work. This older model function generator are usually pretty solid and don't have fuses so if they're broken then they are super broken. After some initial tests just to double check if the TA was not using it correctly, it was found that there was no output for any of the waves.

After taking the thing apart, and I would just like to give kudos to HP for their work in designing their function generator in such a way that it was a huge pain to take apart. I mean this this is a rock solid piece of equipment and my guess is they really didn't want it to be taken apart unless it really had to because it was a mystery box of sliding parts to get this jigsaw box apart. Anyways, it is pretty common for the countless detaching and reattaching of cables to the output by students just naturally wears them down and in this particular case, breaks the connection so that new leads need to be soldered. To the right, there is my handiwork with a new resistor in place. The original connector that was attached was just destroyed so I had to fashion a new connector to the board as well. This actually solved part of the problem because I was able to get the function generator to output a square wave, but the Sine and Triangle wave parts were still flat lining.

Well that was the easy task, now I had to look for something a little more malicious as to why this thing wasn't working and you can see it in this picture to the left. Some old military grade tantalum capacitors leaked and corroded away at the copper trace. On the right you can see that the trace was just eaten away.

So the service manual was found, but wasn't really necessary in this particular case because it was fairly obvious what was the culprit for the bunk outputs. I thought it was kind of interesting though and figured I would show the photo of the schematic, C2 and C3 should be the caps that I needed to replace if I remember correctly.

The only thing that needed to be done to repair this would be to fly wire the two separated traces together and drop in some new tantalum capacitors. Not too tricky.

The above photo is the new wire soldered to connect the two traces, and to the right are the new two orange caps that were soldered in.

And would you know it, everything started working again. Successful repair job to keep this HP function generator up and going for at least another year before someone drops it or something.

Big thanks to Dave Azpell for keeping the service manual and giving me guidance on what to check for to get this guy up and running again.

Update About Myself

So I've been working with Purdue University in the instrumentation room. My job title is Analog Lab Manager. It sounds super fancy and it kind of is. I oversee all undergrad EE labs ranging from sophomore year to senior design for undergraduate engineers. I often fix scientific equipment from oscilloscopes to function generators. I also provide design guidance for seniors in senior design on how to accomplish projects.

As a disclaimer, my views do not necessarily reflect the views of my employer and if there should ever be any questions, please email me.

I do not really like talking about myself all that much and would rather let my engineering prowess speak for itself instead of using sparkly words and posturing to make myself appear superior to my engineering brothers and sisters that worked just as hard as I did.

I am an excellent team leader and work best in teams that prefer open communication to promote excellent brainstorming and design creation. When I get involved in a project I want to think that every team member wants to be involved and want to accomplish the task for themselves and not for a paycheck or grade. Because of this, I tend to expect a lot from team members, but truly I wish that each member on my team feels appreciated for their contributions.

I mostly wanted to post a little bit about where I work and what I do at Purdue University now, but got a little sidetracked with talking about myself a little more than I expected. My current goals now are just build projects for myself to showcase some of my skills, and work my way into the blessings of a professor that would take me on for graduate school.