Yamaha DX-27(S)/DX-100 -1986    Weight = Lbs. Number mfg.= ? MRP=$795/?/$599

User Manual: Yamaha
Reset Proceedures: Test mode Note
Operating System code:
MIDI or other control protocol:
Software related Links: N/A
Patches or knob settings: Cool patch database!
Circuit Overview: below
Scematics/Service Manual:
Common Service Issues/Tips: below
Parts Sources: DX27Keys DX100Keys knobs semiconductors misc
Uncommon chips/modules used: Many
General Info Links: Vintage Synth Explorer

Circuit Overview:
     A digital synthesizer which utilizes special processing chips designed to support Yamaha's FM synthesis architecture. This one having 4 operators and 8 algorithms. The DX100 and 27 synths were further cheaped down in interface but the DX100 has made a big comeback and seems to be the thing to have now, probably because it can be strapped on. And Yesss I know people have gotten a lot of mileage out of that bass sound..but...was it mileage that took them somewhere or mileage that led them around the same scene over and over? :-) I personally have more affection for analog stuff but... for it's day Yamaha did a remarkable job at bringing some very useable sounds out of this whole series of course. Ok well anyway...circuit description..umm..it's a digital synthesizer. Nothing to see here folks...let's move it along. OEM impossible to find parts but fortunately fairly unlikely to fail as with most Yamaha digital stuff.

Service Tips:
     I've found most of these units to be fairly rock solid circuitry wise. Abused units sometimes have solder problems. I've fixed the few I've had in by just going over suspected areas of the circuit boards soldering questionable joints! If anyone needs serious work on these I do have diagrams but...I seriously can't imagine anyone needing..serious work on these since they come up cheap. I fixed a DX100 up recently. Banged up but still came to life after a little solder work and straightening out the mod wheel frame etc. Contacts are very difficult to find now. The contact strip...I'm attempting to use the contact repair kit and we'll see how it goes. Be nice to have all the keys working.

While Yamaha normally does not keep parts around more than 5 years or so, I stock what I can. All out of dx knobs.
Contact Sound Doctorin'

Test Mode Notes

Here is a bit from the manual in case you need to reset one of these machines. From my note to sdiy:

The manual says:

When the test program is executed, the voices in the internal RAM area and voice number in the 96 voice number bank area will be erased. Please be sure to save the voices in the 24 internal RAM area on to a cassette and write down the voice names of the voice numbers in the 96 voice number bank area before executing the program. Also the programmed message that is momentarily displayed when the power switch is turned on will be erased, therefore write it down.

------- Hehe. Gotta love early MIDI synths here and there. Anyway it runs you through all the test programs and you need midi in and out connected to proceed there and amp with 10dB gain between cassette in and out jacks and Breath controller hooked up and footswitch. To enter the mode you press 1 and 2 voice select switches while powering on Then it gives you a prompt and you press +1 to proceed but also you can split the tests up by booting instead with 1 and 3 OR 1 and 4 instead of 1 and 2 held down. 1 and 3 will execute only the first 5 tests and the 1 and 4 option will do the remaining ones instead of the first 5 tests. (6 through 9). The moment it enters the test mode all RAM stuff will be returned to factory settings I guess. SO maybe that's the ticket if you don't have any data to save. Otherwise looks like a lot of work.-Bob