JX3P pitch bender not working

[otto]

The pitch bender doesn't work. I've opened it up and nothing obvious is wrong, unplugged and re-plugged the connector (LFO button is also connected here and works fine). I'm contemplating re-soldering the connections but beyond that I don't know. I read something about the ability to turn the midi to bender off through a button combination but I would assume that only applied to external midi control over the bender.

The bender appears to control the pot magnetically, something I'm not very familair with...

[rhino]

first thing that comes to mind is IC4; a 14051 MUX. next would be IC3; a dual-op amp.

DMM pin 1 of IC4 on the button board while moving the bender... should go from 0v (center) to +5v (either way)

Then scope pin 3 of IC4... should be a pulse-train with one segment rising and falling with the bender notion.

next, scope pin 8 of IC 5 (the op-amp follower) and look for the same type pule there.

[otto]

Thanks for the info. I'll check it out.

[otto]

Ok, I'm not getting anything on pin 1 of IC 4. Will this work:
http://www.mouser.com/ProductDetail/ON- ... ZEi3zmeJIo

[rhino]

if you get no voltage change on pin 1 og IC 4, the pot might be dead....broken wiper??? it's possible but unlikely that the IC input would short tight to ground.

check the pot: + on one side, -on the other, ground in the center,
DMM pin 6 of IC 3. if voltage goes from - to + wiuth bender motion, then start by changing IC 3.

[otto]

ok, it appears the pot is working and pin 6 of IC3 does go - to + with bender motion so the likely culprit is IC3?
Thanks again for your help.

[rhino]

all right.
pin 7 of IC 3 should not smoothly follow the bender, but should 'jump' to -15 or +15.
pin 1 of IC 3 should vary with the bender. if not, replace IC 3
if it DOES, try (again) pin 13 of IC 4. if nothing there, check D 41

as last resort, replace IC 4. The one you posted about is the same internaly, but you need a DIP plastic package.

[tupinamba]

Hi !
Digging up this thread because I'm also trying to fix a non-working bender...

Here is as it goes :
Nothing changes when bending up. But when bending down a few millimeters, it abruptly bends down a lot, then stays this way until bender is down.

I've checked the pot : it seems OK (0 ohm when down, around 82 kohms when up, around 41 kohms when at rest).

I replaced IC3 (4558), IC4 (4051),TR11 (2SK30A) and D41, but problem isn't solved.

On IC3 pin 7, where I should get -15v when pitch bend is down and +15v when pitch bend is up (and I guess around 0v when in its middle position), I get -12v at rest, still -12v when up, and abruptly +14v when moving the pitch bend stick a few millimeters down, and then voltage doesn't change (accordingly to the sound)

IC4 pin 1 stays around 0v when moving bender up or down.

IC4 pin 3 looks like this :

Bender at rest :


Bender up or down :


IC5 pin 8 looks like this :

Bender at rest :


Bender up or down :


If I get it right, the problem is that I should have 0v on IC3 pin 7 when bender is at rest, and -15v or +15v when moving the bender. So the fact that it abruptly goes to +14v seems normal... but it should do so from 0v, not from -12v...

Any clues from the experts?...

Thanks in advance !

[tupinamba]

UP... Anyone ?...

[Montoya]

UP... Anyone ?...

I’m refreshing this thread because I have the same issue, identical symptoms except it’s evident when bending up (instead of when bending down like Tupinamba’s )

After reading the text it seems the obvious chips have been swapped, I would have suspected the cmos chip (4051) as well. I suppose if the cmos chip was blown, and the replacement cmos chip wasn’t handled with care (static discharge is usually what destroys these chips) maybe the 4051 is the issue?

Were you able to sort this out?

Thanks in advance

[synth80s]

UP... Anyone ?...

Did you ever figure out the problem? I have the exact same issue and have also replaced IC3 and IC4.

[MusicGearMD]

FWIW I just fixed a JX-3P with the same symptom (pitch abruptly changes at the midpoint, but no bend) and it was caused by a failure of the LM311 voltage comparator (IC20) on the main board.