“Yamaha DX21 MIDI Digital Programmable Polyphonic Synthesizer.
Comes in a 5 STAR flight / transport case which is in top condition (and the keyboard will be shipped in this) which must be worth at least £60.
I have tested all I could on this keyboard :
The screen works ok – there are some black bits at the top and bottom of it that I have tried to show in one picture.
But it does not affect the area where the text is displayed.
All the piano type keys are working properly
All of the green buttons work – i.e. they make whats shown on the screen and the sounds change.
The volume and balance sliders work, and so do the modulation and pitch wheels
The headphone output and A&B outputs are producing sound.
I have not (and cannot) test all the other sockets at the back of the keyboard.” Click here to search for synths on eBay
“YAMAHA DX-21 Vintage FM Synthesizer. Made in JAPAN-1984 Works Great With Box. ” 
” Yamaha DX21 MIDI Digital Programmable Polyphonic Synthesizer.
“Yamaha DX21 Keyboard Synthesizer. Condition is “Used”. Works perfectly! The keyboard is missing the second slider, but other than that, the keyboard turns on and plays perfectly. I love it but I’m just selling it because I need the cash.” 
” Previously owned NOT WORKING PROPERLY Yamaha DX21 Digital Programmable Algorithm Synthesizer
“Yamaha dx21 has a history of being a tank and has some awesome retro and sounds! Super Clean!! ” 
“Vintage Yamaha DX 21 4 Operator FM Synthesizer Keyboard Synth Polysynth . Condition is Used. ” 
“You are bidding on a previously owned and in working condition Yamaha DX21 FM Synthesis 8-Voice 61-Key Keyboard Synthesizer. This auction is for the synthesizer you see pictured. Nothing else included. It comes as pictured. Please take a moment to look at the pictures and assess the unit. It has some scuff and scratches from use. The pitch/mod wheels are both a little bent. They both work, they are just a little sideways. It has been tested and is in good working condition”
“Yamaha DX21 FM Synthesizer. It works but the problems are. 4 or 5 keys does not work. They feel great but no sound. The main edit button does not work. It turns on and you can play sounds except for the keys that do not work. That’s why it’s listed for parts or not working. Its my understanding it may only need a cleaning on the inside to get the keys and button trio work but I’m not 100 sure. ” 
“Seller Refurbished
“Yamaha DX21 Vintage FM Synthesizer . Condition is For parts or not working. Found in a house clearance, I don’t know much about these, vintage Tamiya is my thing. I have powered It up and it says check battery, so unable to test. Was found wrapped up well and In a dry place so I think that with a new battery and some attention could work again” 
“YAMAHA DX21 DIGITAL PROGRAMMABLE SYNTHESIZER KEYBOARD PIANO . Condition is Used. Been in my possession for 30 years. Has recently become temperamental with voices loading on power up and as of now they always eventually load. Also temperamental with individual tuning, not all voices load to A/440. All keys work and all factory voices load. New battery and battery holder. Sold as is.” 
“YAMAHA DX21 DX-21 FM Digital Synthesizer Vintage 80’s that powers on and has output, but two keys won’t spring back up and LCD has minor clouding as shown. Offered for parts/repair.” 
“Everything works and sounds awesome. ” 
“YAMAHA DX21 FM Synth Keyboard in overall very good condition. Please note, however, the left end piece had a top part slightly cracked and was glued back in place (see last photo.)” 
“Yamaha DX21 Vintage Synth keyboard. Condition is Used. ”
“Yamaha DX21 Synth for sale
“1980’s Yamaha DX21- 61 Keys Keyboard Synthesizer . Condition is Used. Shipped with USPS Priority Mail.
“…Yamaha DX21 Synthesizer Keyboard Ser#2766 Great Condition!
“Yamaha DX21 vintage synth
“Yamaha DX21 Synthesizer Keyboard. Condition is Used. Comes with a wood Case. Has a crack on one of the sides but still fully functional. Also if you’re into talkboxing i have the presets saved.”
“from estate, has been in storage a long time – powers comes on and display shows solid blocks across the top, no output, no functions work at all – unit being sold as is for parts or repair project ”
“Yamaha DX21 Vintage FM Synthesizer Synth . Condition is Used.
“Yamaha DX21 Vintage FM Synthesizer Synth . Condition is Used.
“Yamaha DX21 Keyboard Synthesizer With Foot Pedal And Mouth Controller. Condition is Used. Liquid crystal Display (pictured) not working correctly (a portion of the screen is black, but can read the middle). Missing a slide knob cover (pictured) comes with original factory programming cassette and keyboard to tape connection.”
“Perfect working condition. Incredible vintage sounds that you can’t find anywhere else.” 
” Yamaha DX21 digital synthesiser from the late 1980’s, in good working order.
“A Yamaha DX21 FM synth, perfect audio and everything 100% works. Only some very minor wear, other than that not a single thing wrong with this beautiful piece of equipment. Lightly used and well taken care of.
“Yamaha DX-21
“Yamaha DX21 Digital Programmable Algorithm Synthesizer for parts/repair. Has some keys that need to be replaced and needs a new power cord. Most of the features appear to work so with a few minor repairs and a clean up and this should be ready to go. I am not an expert on this synth but I did test the functions that I understood and it is producing sounds. I am available to answer more specific questions regarding this item so please ask to get a better understanding of condition if needed. ”
“There are rust in several places on the back side.
“Selling DX21 USED 100% FULLY WORKING
“This is a listing for a used Yamaha DX21 Digital Keyboard loaded with Talkbox Patches. It comes with nice Road Runner gig bag and attached power cord. There are no other software or CDs included. It is being sold as is in good condition. ”
“YAMAHA DX21 sold as is
“This keyboard powers on but no sound, see pictures for details as they are part of the description”