Yamaha DX7IIFD dead key octave

I bought a faulty DX7IIFD with hopes of repairing its problems. First on the list is a group of twelve keys that don’t play (middle C# up to C). The traces on the keyboard’s circuit board appear clean with no breaks. I have not disassembled the keyboard assembly itself to inspect contacts, etc. (Removing and replacing all the keys is a little daunting.

Any suggestions?

Additional problems are left channel only in headphone jack, volume slider doesn’t function in the low range, and the floppy drive transport doesn’t let disks “thunk” down and seat properly.

I would double check the key contact c.board, not only with a lighted high power lighted magnifier but electrically with a good quality meter,it doesn’t lie. A group of keys out like this is almost always a bad KCC board. think on it,theres not much else it could be other than a broken wire/pin thats connected to the KCCboard… Don;t trust your eyes,lol,trust the meter

@hawgford Thank you for the reply. It will be a couple of weeks until I can get to it, but I will take your advice and post a follow-up.

sounds like somebody has already been inside and perhaps didn’t reconnect everything from their investigative attempts. When you get to it, proceed as if someone didn’t put it back together properly so you don’t damage more things.

@hawgford Could you please provide more details on how to use the meter to check the keyboard circuit board? I’m assuming it involves checking for continuity, but I’m not sure how to go about it. Any info is appreciated.

Update on the dead key problem: The 61 keys are grouped into five “switch assemblies” (parts 8-2 and 8-3 on the DX7II parts list, page 5), which connect to the keyboard circuit board (part 8-1). There are four 12-key assemblies and one 13-key (the lowest C to C octave. Subsequent ones start at C#). Each one has two metal prongs (one at each end) that are through-hole soldered to the board. I was checking for continuity when I discovered that one of those prongs was detached. The solder joint still looked solid, but when I was attempting to reflow it, the prong fell away. Removing the switch assembly from the board, I discovered that corrosion had eaten right through the prong, cutting it in half. I soldered it back together, reinstalled the keyboard, and the dead keys were back! One flaw remains with the key nearest that prong (middle C#): the output is low. I suspect it’s due to corrosion in that area, which is difficult to remove without completely disassembling the switch assembly.