4051 mux failure? MC-505

Pulling out your hair? Don't know what to do or where to go? Ask in here.
Forum rules
READ: VSE Board-Wide Rules and Guidelines

If your Help request has been solved, please edit your first post in order to select the Image Topic Icon to let others know your topic has been solved.
Post Reply
User avatar
Synthetech
Junior Member
Junior Member
Posts: 185
Joined: Sun Oct 07, 2012 4:28 pm

4051 mux failure? MC-505

Post by Synthetech » Sun Jul 06, 2014 12:06 am

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.

User avatar
Synthetech
Junior Member
Junior Member
Posts: 185
Joined: Sun Oct 07, 2012 4:28 pm

Re: 4051 mux failure? MC-505

Post by Synthetech » Sun Jul 06, 2014 1:32 am

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.

Image


This is the suspected 4051 IC

Image

Borsek
Newbie
Newbie
Posts: 1
Joined: Sun Sep 04, 2016 1:28 am

Re: 4051 mux failure? MC-505

Post by Borsek » Sun Sep 04, 2016 1:34 am

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!!!

Post Reply