[sdiy] edp wasp dead key group (cmos issues)

[Julian]

Hello, 

Im trying to fix an edp wasp.

The lowest c is fine, then c#, d, d#, and e are dead.  All other keys are fine.

This specific of 4 dead keys is fed into one half of a 4052 multiplexer, then to a 4016 switch, and then to a 4028 and onwards.  The other group of 4 keys also utilising the other halves of the same ics are working fine.

My problem is determining, with my multimeter, which ic to replace.  

Can anyone give me some pointers as to how to diagnose this.

Laurie's redrawn schematics are usefull:

http://www.elby-designs.com/wasp/keyboard.pdf

Cheers, Julian


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