Adventures in creating and destroying sounds
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  • Installing a New Battery in a Yamaha DX7

    Posted on September 26th, 2009 Bob 36 comments

    I recently had the chance to replace the battery in a Yamaha DX7 Synthesizer. The manual for the DX7 states that the battery should last for 3 to 5 years and it was well past that time. I first thought that I could just run down to Walgreens and pick up a “button” style battery and pop it in but after poking around on the Web, I found out that the DX7 uses a special kind of CR2032 battery with solder leads mounted on it. I found a suitable battery through Mouser (part number 614-CR2032FH-MFR). To replace the battery you basically have to take the whole synth apart, but Yamaha tries to make the procedure as painless as possible.

    I found some very helpful instructions through Dave Benson’s DX7 Page (also archived here) for replacing the battery. These instructions were spot-on!

    There were a couple of things I noticed while disassembling the synth.

    1. The connector labeled C6 on the main board is not connected to anything.
    2. The main board was a little difficult to remove from the chassis after all screws and connectors were out. There are two tabs that are used to mount keyboard. You have to angle the main board between these tabs and the back of the chassis to lift the board out. Be careful when doing this!
    3. To remove the old battery, I used a solder sucker to get rid of most of the old solder which makes it easier for the old battery to pry up and out.
    4. The battery evidently had been replaced before. There was a service sticker from some repair shop on the back of the unit. The trace between the battery’s positive lead and the next component (which is a diode) had been severed. I had to solder in a short jumper over the trace to fix it.

    Overall, replacing the battery was not a difficult task but somewhat time consuming. Have fun!

    You can click on the images below to get a larger image:

    Yamaha DX7 open with keyboard in place

    Yamaha DX7 open with keyboard in place

    Yamaha DX7 close-up of connector C6

    Yamaha DX7 close-up of connector C6

    Yamaha DX7 open with keyboard removed

    Yamaha DX7 open with keyboard removed

    Yamaha DX7 main board

    Yamaha DX7 main board

    Yamaha DX7 solder side of main board near battery

    Yamaha DX7 solder side of main board near battery

  • How neat are on-board pots?

    Posted on February 14th, 2009 Bob 1 comment

    onboardpots_508I build a lot of pedals. Probably my least favorite thing to do when assembling pedals is wiring potentiometers. I found a great way to cut down wire cutting, stripping and soldering time greatly by just using the right angle PCB mounted pots as opposed to ones with solder lugs. Of course, I’ve had to reconfigure PCBs to accept the new-fangled pots but the pay-off is well worth it!

    onboardpots_513To make mounting easier when using the PCB mounted pots, I got a small cardboard box and made a cut-out in it a little smaller than the circuit board. Then I taped on strips of cardboard right on the edges of where the circuit board will actually fit in… the height of the cardboard strips keep the pots pretty close to a right angle when soldering everything down.

    Since the pots are usually a bit mis-aligned when you start soldering, I typically solder one of the legs in place with just a small amount of solder while holding the pot in place with my fingers. I make sure that the pot’s leg is flush with the pads on the PCB and everything is close to being centered and straight. After the solder cools in a second or two, I remove my fingers. Now technically this would be considered a “bad” solder connection because I might have moved my hand while the solder was cooling. Not to worry. That’s why you need to use a minimal amount of solder here. Just enough to “tack” the pot to the PCB. I then go to the unsoldered leg on the opposite side and “properly” solder each of the legs… and then the last one with the presumably “bad” solder connection. Now all three of the legs should be soldered on there properly!

    Sometimes, the back of the pots hang over part of the circuit board with pads and traces. Just to make sure nothing shorts out on the back of those pots, I usually squeeze a bit of hot glue between the back of the pot and the PCB just to be safe. Just a little dab will do ya!

    onboardpots_342I also recently reconfigured a pedal to take PCB mounted pots with straight (i.e. not right angle) connectors. I’m still working on a more streamlined way to solder these, but so far it’s been pretty smooth sailing!

    The only thing left to tend to is to make sure that your enclosure has holes that match up almost exactly with the pots. Make sure to measure, double-check and measure again! I usually make the holes in the enclosure a little bit bigger than normal (but not too big, you don’t want the holes to be exposed under knobs!). It’s super nice not having to wire a bunch of pots!