Yamaha DX-21 -1985    Weight = Lbs. Number mfg.= ? MRP=$795/?/$599

User Manual: Yamaha
Reset Proceedures: N/A
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: Keys 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. This is the cheap DX to have for the dynamic possibilities! Cool effects attainable by using the layer pan slider and it has a more succinct envelope control than the DX7 giving better attacks I've been told and seem to hear as well on mine. Definitely a lot of fun for the mon. :-) The typical VLSI chips that seldom see problems in this series so not much point going into actual circuitry descriptions here.

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! I had one laid aside for a long time that would randomly lock up. TURNS OUT you have to have screws in the back to close the ground circuit to things on the board. I fortunately finally had my unit open for battery replacement and found the discrepancy between the two. Trying to work on the unit with the board loose so I could easily pull it up to check things. lol. Anyway with the right two screws in it worked much better but eventually glitched and lost memory! Of course it is nice that you can restore factory banks from ROM on these! But anyway with all 4 screws in the back it seems to be stable again. yay. After making wood sides for the otherwise nice unit that was missing sides I hated to toss it.

While Yamaha normally does not keep parts around more than 5 years or so, I try to stock what I can. Out of dx knobs
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