Diodes on Yamaha Music keyboard query.

[geobee]

Hi all, just wondering if anyone would know the purpose of the string of diodes, think they would be the old 1N914, on the key circuit strip. The diodes are off the carbon track switching pads. Any ideas would be great.

[Moshly]

Look up N-Key rollover

[capt bullshot]

My guess:
The diodes are used to decouple the key switches for a multiplexed scanner. If they weren't there, pressing multiple keys at the same time would short out some of the scanning lines and the keyboard scanner wouldn't work. Using the diodes enables the scanner to detect any number of simultanously pressed keys.

[LateLesley]

It'll be part of the keyboard matrix.

There's an example halfway down this page - http://musicfromouterspace.com/analogsynth_new/OLDIESBUTGOODIES/CONTROLLERS/scanningmatrixkeyboard2.html

[geobee]

Many thanks to all, well explained. Looks like they are just performing a ''one way street'' from the keys.