4051 mux failure? MC-505

[Synthetech]

I have a roland MC-505 that developed an issue where the Mixer Fader's for Parts 2 & 3 will not operate.

I can see all the others move the little GUI faders on the LCD screen, but 2/3 will not move at all when I move the actual sliding pot.
The suspected 4051 8 channel mux/demux'r services Mixer Faders 2,3,4,5,6,7, LFO 1 Depth and Portamento Time

Mixer Faders R & 1 are serviced from a different 4051 and work fine.


I suspect the 4051 has failed on channels 7 & 6 (what the Mixer Faders 2/3 are connected to), but thought I'd ask in here if anyone has seen a 74HC4051 fail partially like this?


There's about 3 or more 4051's inside the MC to mux the many pots on the control panel. All the others on the same data buss are working fine, just these two faders are inop.

[Synthetech]

if it helps any, I did confirm both pots are connected to the +5v and G each.
also, their wipers have clean connection to pins 2 & 4 on the 4051.

So all connections are good on the pots side to the IC.

Here's a pic of the board for reference.
Huge board.. it barely fits on my Panavise.




This is the suspected 4051 IC

[Borsek]

Hi!
I recently bought a roland mc 505 and i have the same problem with you, i have removed the potentiometwr 6 and 7 of part mixer and y turn on the 505 but im having the same problem, please if you fix that problem or anybody knows to fix it, do a reply on this post.
THANKS!!!