Boss SP 303 Pad Repair

I bought a Boss SP 303, which was obviously used. It showed up, and it smells like either a musty arcade, or somebody’s basement. Clearly the SP has been in storage for a *long* time, and I’m not sure that the scent is going away. The description for the SP 303 was Very Good condition, but when it arrived some of the pads were shot. Most importantly, the record pad just wouldn’t work at all.

Here you can see that the SP 303 isn’t in awful condition, but it’s also not Very Good by my idea of Very Good. The rust you can see on the bottom leads me to believe that the SP 303 was kept someplace damp, and I may decide to sand blast and repaint the sides to repair it.

Here’s the other side…

Surprisingly the bottom has faired much better, possibly from the rubber feet keep it from getting banged around too much.

At any rate, you’re not here to see what the case looks like I suppose, and I figured this wasn’t the end of the world, and I should be able to repair the pads as long as the PCB traces were still in tact. The device looked pretty simple, and I couldn’t imagine the technology inside it was anything terribly sophisticated.

I wouldn’t try this at home unless you know what you are doing (ie powering it on without the case on), but below you can see I took it apart while trying to test things out, and you can see it is just two PSB boards, so yeah, it’s not too bad. My initial guess on why the pads were not working was because either the contacts on the PCB were oxidized or otherwise dirty, or the pads themselves had the conductive material worn off of them.

To just try out a few things, I moved the sheet around and positioned different pads over different parts that weren’t working. Notably, the B bank button, and record were not working. I took some rubbing alcohol to the circuit board, and I ended up getting a lot of graphite off of the contacts. Likely this was from the pads, but it’s also possible that the contacts are coated with a graphite paint or something. I’m not sure, and didn’t bother to find a service manual or anything that might describe it. So for what is coated on the PCB traces, your guess is as good as mine.

Taking the SP 303 Apart

Yeah here’s the picture of the bottom again. Before you can get the case off you’re going to need to take these 5 screws off. These five screws hold the top and bottom halves of the case together.

Here you should be able to find the two screws on the back, and these hold the lower PCB that has the brains of the SP 303 to the back of the bottom part of the case. So before you can proceed remove these two screws as well.

My SP 303 didn’t come with the SmartMedia face plate cover, so you might need to remove these two screws as well. As you can see, I just have an exposed SmartMedia card… *shrug*. The two screws are on the bottom of the SP 303… but just take a look for yourself.

Once you have the screws off, the SP 303 should open up pretty easily. Go slow as there are ribbon cables connecting the two PCBs together, but it should not come apart hard. From here you’ll be able to see the five screw holes/mount points from the bottom of the SP 303 PCB.

Once you have the two halves separated you’ll see that there are eight more screws you’ll need to remove. Hint: One of the screws is under the plastic plate. You’ll also want to make sure that you put that metal piece back on that is in the top left screw. I suspect that this is for grounding or something, but I didn’t spend much time figuring out what function it provided. Just make sure you put that metal tab and plastic shield back in place 😀

Once you’ve removed all the screws, you can now pull the SP 303 PCBs out of the top half of the case to expose your pads.

At this point, it’s probably a good idea to do whatever cleaning you were planning on doing. Scare off the dust bunnies, knock back any grease or beer. Whatever you find that shouldn’t be there can go. I’d suggest using rubbing alcohol for this cleaning process as it dries quickly and is less likely to cause you issues with conductivity or causing rust when you put the SP 303 back together.

Pad Repair

In my case, upon close inspection, I could see that the graphite or conductive material was broken and worn out on some of the pads. So I figured I’d give CaiKote 44 a try. It’s fairly expensive, but 1g of this silver/carbon based “paint” should last you a good while. I did find that the included swabs were a bit messy to work with even though I soldiered on. If I did this again, I’d probably choose to use some small paint brushes instead because the cotton became a bit painful to have to keep trimming so that it wasn’t getting the contact solution all over the place.

Even though only a few of the pads were non functional, I decided I would just apply the CaiKote 44 to all of them while I was inside so I would be less likely to have to come back again later to do this. The package says it dries in about 15 minutes, and gives some curing instructions with a bulb, but I figured I’d just let it dry out for the day.

In the above picture you can see that I got paint all over the place as well. Just to be save, I scrapped the excess paint off with my Swiss army knife. It flaked off very easily and I ended up with the paint being applied only to the pads. I then carefully powered on the SP 303 while it was still outside of the case, and tested the pads. A few of them were still behaving a bit off, or required a bit more force than I expected.

To fix this, for a couple of the PCB traces I just used a graphite pencil and drew on top to see if that would help. Below you can see for the Bank B pad (SW35) I just drew on top of it. I got a bit outside of the contact traces, but I did get a magnifying glass to make sure I didn’t short anything. I would save this as a last case solution, because honestly, these traces look like they should work.


Well I am now able to use the SP 303 as intended, and as far as I can tell, all of the buttons now work. So anything that comes out of it that sounds poor is likely my fault, and not the SP 303’s fault.

If I have any problems with the CaiKote 44 flaking off I’ll definitely make sure to update this post, but for the time being it has definitely been holding up.

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