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

[Harry Bissell Jr]

Well Julian, personally I'd kick your
@ss and tell you to get a scope.  :^P

Not being a cruel man (well the x-wives might
not agree...) my best suggestion would be to drop the
keyboard clock speed way down by making the timing cap
(temporarily) much larger. Then maybe the meter could
pick it up.

A logic probe could also be used. You could make one
from some CMOS inverter package and a LED, I'm sure
there are designs out there on the internet.

Look to see that the 4028 IS addressing the chips
correctly.

Look carefully at pins 9, 10 of the 4052.  A bent
under
pin , bad solder joint might cause this ofr sure.

H^) harry

--- Julian <julian at 22host24.com> wrote:

> 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
> 
> 
>