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Looking for circuit diagrams for yamaha dx21

All voltage rails ok. audio sections "live".......battery was dead.Thanks. Would love to get the circuits....Regards Terry

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Have you managed to locate a DX21 service manual yet?? What problem are you experiancing with the 21?? From your request notes you mention 'all audio sections are live', do you mean that you have no audio from the 21?? Most faults i have experienced with the 21 are, failure of the main OPP YM2164 fm chip and associated D/A convertor(YM3102). In some cases YM3102 is ok .When the YM2164 fails, DX21 will boot as normal but no sound whatsoever from the audio out's. YM2164 is the main tone generation ic. Also when YM2164 is replaced, if sounds are reloaded back into the memory areas from ROM and the display reads gibberish in certain memory areas then a ram or rams have failed also. The crunch, Don't expect to get a YM2164 and Associated components easily, these things are very rare. I have seen the YM2164 fetch £35!! Best way around this, if you are eager to repair the synth is to purchase a working YAMAHA FBO1 FM MODULE ,not a popiular module and sell for about £20 - £50 on ebay. You can rip the parts out of the unit and use them in the 21. Sell whats left on EBAY spares or repairs.
The damaged (i believe) is caused by failure in the powersuppy causing voltage rails to 'spike'. What is strange is the cpu stays in tact. Capaitor replacements can cure this problem. I have a complete circuit diagram i can scan and email to you for a small fee for my time if required . email me:- proteus4@blueyonder.co.uk

Posted on Mar 08, 2009

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