Reviving the Yamaha DX7s, part 1

Yamaha DX7s

I wish I had been taking pictures of this whole process. In case you haven’t been following along, I have a Yamaha DX7s which, since it’s “inception” in the late 80’s, has seen many owners and a lot of disregard. Two keys were broken, along with the pitch wheel being “wobbly” and the battery needing to be replaced (considering the amount of leaked acid on the battery, I’d guess for several years). Since I know the value of the DX7 (a really impressive partial list of users can be found here) I took it upon myself to “revive” this one.

For those not familiar, the DX7 is a digital Polyphonic (but monotimbral) FM Synthesizer made by Yamaha starting in 1983, and (arguably) the highest-selling synthesizer ever made. This success is for very good reason: it has a lot of performance options, was one of the first keyboards to feature MIDI, and uses FM (instead of the Subtractive Synthesis used by most Analogue Synthesizers) to generate a huge variety of sounds from very “pure” sine waves to quite complex pads, percussive sounds, and textures (not to mention really sweet bass). A bit after the original DX7 came out, Yamaha made a number of HUGE improvements (added stereo outputs, bi-timbrality, improved MIDI, and more) and released the DX7 II. The problem was that the DX7 II was too expensive for most musicians, so they released a “slightly scaled down” mono version more designed to be used on stage, and called it the DX7s. This is where my synth falls…

So I found a “how to change the battery on a DX7” tutorial, and ordered my replacement battery from Yamaha. It came less than a week later, and I opened up my synth. Since the “s” model is a different revision than the “Mk I” DX7, I found that MOST of the actual “disconnect this wire next” parts of the instructions didn’t match up. On the other hand, there is enough useful information in the above referenced guide to get you started if you are patient, intelligent, and careful (well, two out of three ain’t bad..). I started by flipping over the unit and taking the bottom panel off. After that it’s pretty obvious which board is the “motherboard” (it’s the one that’s about 8″ by 5″ in the middle toward the left side, with ALL the wires connecting to it).

To remove the motherboard, I *carefully* disconnected the cables from around the edges first. It’s pretty clear where all the wires would connect back up, but some people would go as far as to mark them with tape or something. I am not one of those people, so I just disconnected them. Next I removed ALL the screws on the back (there are 3 around the MIDI jacks on the back and 2 more over by the audio jack). Make sure you find a safe container to keep your screws in, organized by where you took them from if possible – there are like a zillion screws in this thing, and it’s easy to forget where you got them if you just throw them all together. After all that is done, the motherboard is still attached by two “different” screws, accessible through holes in the motherboard itself toward its left side. Once that was done, I carefully lifted the board off and set it on a static bag while I worked on it.

The battery is pretty obvious here, but note that this battery is special and you can’t just buy one at Target or something. It

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has two little permanently attached legs, but it otherwise a normal CR2032 disc battery. Some people remove the whole thing and attach a battery holder and then put in a normal CR2032. Some people (somehow) leave the legs attached and pry out the battery itself, and then replace it with a normal CR2032. I ordered a new actual DX7 battery from Yamaha. To each his own, I guess.

Removing the old battery and soldering in the new one was really not that hard. Granted, if you haven’t done any fine soldering before, and/or don’t have all the necessary equipment to safely/properly do that, you should really let someone else do it, but it’s not that hard. After that fun, I put the keyboard back together and turned it on, and everything was A-OK…

…except that I had totally forgotten to fix the two broken keys (including ordering them from Yamaha!).

So I ordered the two new keys, and waited. Meanwhile, I took the synth back apart. To get to the actual keyboard assembly, you “simply” remove everything above it (with the synth flipped over, of course). This means the Motherboard, the Power Supply board, and the Key-contact assembly. Like I said, about a zillion screws. I wasn’t careful when I removed my keyboard assembly (I was lazy and didn’t remove all the cables) and broke the thin ground wire where it attached to the assembly itself on little solder tabs on the end. So this is a warning: REMOVE ALL THE WIRES FROM THE KEYBOARD ASSEMBLY. This will help you avoid a lot of unnecessary wear-and-tear on the “guts” of your keyboard. Thankfully, with more careful soldering, I was able to fix the ground wire (I think..).

While I was waiting for the keys to come, I took off ALL the other keys and cleaned out 20 years worth of grime from on, in, and around, the keyboard assembly. It was pretty nasty in there, but the exercise not only gave me something to do while I waited anxiously for the keys to arrive, but did help improve the action of the keyboard quite a bit. Finally yesterday the keys arrived, and I attached them (I really wish I had pictures here..the keys have a metal spring-bar thing under them that sort of pushes on a little slit in the casing underneath the assembly. You have to sort of line up the spring first and then push the key forward and down and it snaps in. If you have one in front of you you’ll see what I mean).

Once that was done, I took off the pitch wheel assembly, and found that the wheel simply needed to be “snapped” back on. I did that and adjusted the nut on it for the right tension feeling when moving the wheel, and then put it back on. Then I put the keyboard all back together and turned it on in my studio.

The keys felt really nice and springy again (and ALL of them worked right), but when the synth turned on it showed the normal

>> Yamaha DX7s <<

screen, followed by

Change battery!

I was rather confused/frustrated by this, but at that point, I had to go to bed.. maybe tonight I’ll pick up where I left off on that one and figure out what’s going on…

The saga continues in Part 2.

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