Monday, October 28, 2013

potentiometer magic

Since using it with the Titan Ups, for about the fourth time now I've had to replace the tune knob on my Roland EP 7-II digital piano. The first time I did it I called around and got estimated to fix it for $100, plus parts. I looked a little further and found the part for $7 at a local shop and decided to try my hand at soldering it in myself. It's a a terrible design, and perhaps a terrible tuning potentiometer as well, as this part repeatedly breaks and makes my tuning go totally wonky and sound like crud.

Tomorrow I need to working to lay down some piano tracks for a recording the band did a while back, overdubs and perhaps re-dubs, or maybe just dubs, as it is a rocksteady reggae band. Tonight I spent about two hours opening the keyboard up and doing a total hack job soldering the new part in. This blog entry is a record to help me remember the steps in repairing it next time... and maybe help someone else.

 In the photo above you can see the tune knob and it's design where it sticks out from the back of the keyboard by quite a bit. This sucks. I drag this thing back and forth to practice and then about once a month to various bars around San Francisco. There is nothing to protect this knob from beating on the sides of my case and it eventually gets roughly tossed in the case in a frantic load-out off a stage somewhere and it destroys itself.

The idea that a keyboard needs a tuning knob is kind of ridiculous, but since it's there, it would be fine if the damn thing was flush with the back. But it's not, and when it breaks it tends to float down in tuning almost a full step. really, really annoying. We just played a show and I kept a guitar tuner on it to tweak between songs, and it fell out every song. So, here is how to replace the bastard:

First off, remove all the screws from the bottom of the keyboard. Keyboard will upside down, and you will have the foresight to put a towel under it to protect the keys. There are maybe 20 screws, and of these four are longer ones. I put pieces of gaffer's tape on the case to remember which holes take them. Also, two of these long screws don;t need to come out, but I forget which they are, I think the outer two. Sorry.. I took pics after almost put it together and thought blogging it might be useful. Put these in one bowl.

ramekins, good for baking flan and screw sorting
Look in at the main board (it's labelled as such) and remove the brass/ brass colored three screws holding the metal heat-sink holder frame on the board to the inside of the keyboard. Then also remove the screws holding it to the back of the keyboard housing. The two long screws are by the midi inputs and I believe there are three other, shorter ones. I put these screws all in a second bowl.

 Remove, GENTLY, the main board and set atop the back of the frame. I put a small blanket under it here. It will still be tethered to other parts inside via wiring. You don't need to undo this.

You can see the knob has two solder points on outer clips, and then three legs that are on inside. you can see the rather sloppy solder job I did last time. Keeps it obvious.

I touch these points with my solder iron until I am able to loosen the old pot and pull it out. I tried to melt out old solder to start with a clean board and holes, but don't have a good solder removal tool. The bulb thing I bought from Radio Shack is useless on a small spot like this.

Sweet salvation in the form of a new potentiometer. Ordered from Syntaur. I've also bought this in San Mateo from CAE Sound. This time they couldn't figure out a part number, so I paid for shipping from Texas.

 old / new

 Get the old one out, and hold the new one in and solder it to the board. Done. You may want to test that it works before you re-attach the 50 screws. I never do and it always fixes it, but then again I am awesome.... Writing this blog took longer than the whole project.
my set up, set up on my stove

If you're still curious, this video talks about cleaning potentiometers. I discovered it while repairing my stereo amp. Not only is this guy showing how to clean volume and tone pots, while sitting on a bed in a motel room, his accent is awesome. I love the way he says "potentiometer", it's nothing short of amazing :


  1. So when I saw the email link to your latest blog on "potentiometer", I thought it was going to be a link to the Halloween costume you told us about on the phone ----- shows you how clueless I am! But very proud of you for being able to do this!

  2. Do you have a part number for those?

  3. also, I cut the extending knob off with a cutting blade on a dremel and am happy to say it's been fine for past couple years. Can still turn with needle nose pliers if needed, but now it's not going to bash itself broken every 6 months.

  4. Could you send me a link where I can order the potentiometer? I couldn't find it on Ebay nor Amazon.

    1. I've been down to this shop in San Mateo (SF Bay Area): CAE Sound

      They might be able to help and ship you one. I haven't used the piano in a few years (quit the band I was lugging it around for) but did find the best fix to be using a dremel to cut off the knob that sticks out. you can still twist it around to tune with needle nose pliers but it won't stick out and get bumped anymore. I strongly recommend doing.. good luck!