Yamaha DX21 power supply repairs

Vudu · Joined: Jun 14, 2005 Posts: 9 Location: Denver, CO

Hi,
Anyone know where to get schematics for repairing keyboards? The Yamaha DX21 in particular. Free would be best.

The internal switching power supply is squealing and the keyboard is not working, although the LCD screen does show something on power-up. The power supply pops out nicely, so if I knew what voltage should be coming out of the various pins I could probably fix it.

Thanks, Vudu
http://www.inthachamber.com

elektro80 · Posted: Wed Jun 15, 2005 12:30 am Post subject:

Give us some time. I am sure we will come up with something.

elektro80 · Posted: Wed Jun 15, 2005 2:00 am Post subject:

There is not one single source for synth schematics.
As for the DX 21 I just made a call to the Yamaha distributor here in Norway, and the service manual is still available. You might want to call Yamaha´s canadian office in order to get the proper part number.

The DX 21 seems to have some components that tend to die. You might find dead DX 21s with working PSUs. These would be really cheap at the moment. Isn´t there a synth repair shop in the Vancouver area you could call about this? Some of the Yamaha product´s from this period did have PSUs with an attitude, so if you are looking for a replacement you should really get the part number or specs.

I have a DX 21 myself. I just might open it up and measure the PSU voltages, but I won´t get time for that yet. friday? sunday? I have been planning to open it up anyway.

Some synths, like the Yamaha DX series, can be hard to repair. It might be cheaper to simply get another unit secondhand.

Doesn´t this one have a fuse? You have checked that one?

elektro80 · Posted: Wed Jun 15, 2005 2:05 am Post subject:

Vudu · Joined: Jun 14, 2005 Posts: 9 Location: Denver, CO

Hi,
Thanks for your attention. The squealing is coming from one of the power supply components, quite possibly the second little transformer, but there are a few other components around it that may be capable of squealing when they aren't happy?

Will see if I can get a hold of Yamaha Canada today.

Yes there are audio repair shops around but I'm strapped for cash right now...

deknow · Posted: Wed Jun 15, 2005 9:22 am Post subject:

most of these power supplies are farily straightforward.

there are likely 3 dc voltages that come out of the thing...+5 (for digital), and + and - 12 (possibly 15, but probably 12). some of the headers on the board (either in the ps or in input to another board) might be marked on the board....there may be multiple instances of some of these on differant wires.

the caps are always suspect, and should be replaced first. always keep the same voltage rating on the caps, but for the main filter caps (there may be only one in this supply...either a big pair, or a big single cap), but you can safely double the capacitence (uf's)...this often takes some ripple out of the dc current, and may make things quieter.

disconnect the ps from the rest of the synth, and test the outputs...if you see +5, -12 and something else, you can bet the something else should be +12. the transformer could also be shot, as could other components. diodes and resistors are cheap, voltage regulators less so (but less than a service manual). personally, i'd start with the caps, and test things from there. if you post a photo of the board, i (or someone else) might have more suggestions. a scope can help, as can a true analog meter (you can see the needle wiggle in a way that is imposible on most digital meters).

deknow

mosc · Posted: Wed Jun 15, 2005 11:24 am Post subject:

Be careful of caps that make any kind of noises - they can explode. Sometimes electrolytics are installed backwards. They can work apparently normally for years and then they start to make noises and explode. Sometimes they skip the noise making phase. The explosions can be quite harmful to musicians and other living things.

elektro80 · Posted: Thu Jun 16, 2005 2:52 am Post subject:

Hey Vudu, that Front & Center - Westcoast Women in Rhyme, Vol. 1 sounds really good. You did that one?

Vudu · Joined: Jun 14, 2005 Posts: 9 Location: Denver, CO

Yes, and thanks! The Front & Center compilation is all my music and production, recorded in my studio - as are all the other CDs on the website http://www.inthachamber.com

Vudu · Joined: Jun 14, 2005 Posts: 9 Location: Denver, CO

Here's some pics of the power supply circuit board, there are no obviously burnt out components. The noise is coming from around the transformer labelled "TYA018".

Voltmeter says:
CN1&2: +5V
CN3&4: gnd
CN5: 0
CN6: -15V
CN7: +15V

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