JTV-69 Volume Knob Behaving Strangely

[mdmayfield]

My JTV-69's volume knob has stopped being able to reach 0% or 100%, and it also takes extra time for the software to reflect the knob's actual position. If I hook it up to the computer with a MIDI monitor, I can see it happening.

This guitar is well out of warranty, but I'm comfortable fixing it myself having built several Variax 300 and 500 transplants. Should I just order one of these? http://www.fullcompass.com/prod/240928-Line-6-50-02-0321

Or has anyone seen this behavior before and know how to fix it?

Thanks,

Matt

[mdmayfield]

Here's a one-minute video demonstrating the strange behavior: https://youtu.be/lloyXGpVdFo

[mdmayfield]

So.... I took apart my JTV-69 and sprayed some compressed air on the volume pot's PCB. Now it's working fine.

 

I have no idea if the compressed air was what made a difference, or if there was some strange software thing going on, or what.

 

- It probably wasn't software, at least within the JTV, since I tried unplugging and replugging the VDI

- It consistently followed by blue JTV, and when I tried my sunburst one in the Helix it behaved properly, then switching back to the blue one, the blue one didn't work right again

- Other than taking it apart, nothing else changed besides powering down the Helix and turning it back on

 

So I have no clear explanation for why it didn't work, nor for why it works now. :-/ I will post any other updates to this thread, in case it helps someone in the future.

[davidb7170]

My 69S also does this. It seems to come & go. I can have the issue for weeks, then for a while, it works as it should, then back to the problem. It hasn't become a big issue for me, yet, though, as I have never been one to ride my volume pot on the guitar to change gain. I run it full up and only back it to "zero" during breaks, and if it isn't all the way down, I back my volume pedal on the Helix to zero.

It does it with my HD500 & 500X as well, so it isn't the pedal interaction, it's the guitar. When it's on model mode, it doesn't do it, only on mags for me. My 59 does not do it at all.

I changed out my 69S mags early on for the DiMarzio Paul Gilbert Injector set - noiseless, and love them, but didn't know if that was part of the issue - I am hoping not. I did the swap out in early 2013, and I've only noticed this in past couple of years. Do you have your original pups in, or have you swapped any out? I notice you said it's a 69, so you have the HSS setup? Mine is the 69S with SSS. I bought the 69 interface you mentioned above - reasonable price at full compass, compared to the wiring harnesses for the 59 and 89, btw. I tend to pick up spare parts when I run across them at reasonable prices... It has not become enough of an annoyance to me to dig into as of yet, but when it does, I have the parts to dig in. My initial attack, instead of replacing the whole wiring harness would be to just replace the volume pot assembly first. Everything else is functioning fine, so don't want to got through a total rewire if I don't need to.

It could be a few things, a dirty pot, resistance in a connection, a connector not fully seated, or in a worst case, interaction with the pickups' characteristics. I'm hoping yours still has the original pups, so I could possibly rule that factor out with my replacements.

I've been watching the forum here, and yours is the first mention I've seen that sounds like the same thing I'm having. Wonder what psarkissian would have to say about this - I'd be interested to hear if he's run into it before on units he's had to deal with....

Dave

[mdmayfield]

My 69S also does this. It seems to come & go. I can have the issue for weeks, then for a while, it works as it should, then back to the problem. It hasn't become a big issue for me, yet, though, as I have never been one to ride my volume pot on the guitar to change gain. I run it full up and only back it to "zero" during breaks, and if it isn't all the way down, I back my volume pedal on the Helix to zero.

It does it with my HD500 & 500X as well, so it isn't the pedal interaction, it's the guitar. When it's on model mode, it doesn't do it, only on mags for me. My 59 does not do it at all.

I changed out my 69S mags early on for the DiMarzio Paul Gilbert Injector set - noiseless, and love them, but didn't know if that was part of the issue - I am hoping not. I did the swap out in early 2013, and I've only noticed this in past couple of years. Do you have your original pups in, or have you swapped any out? I notice you said it's a 69, so you have the HSS setup? Mine is the 69S with SSS. I bought the 69 interface you mentioned above - reasonable price at full compass, compared to the wiring harnesses for the 59 and 89, btw. I tend to pick up spare parts when I run across them at reasonable prices... It has not become enough of an annoyance to me to dig into as of yet, but when it does, I have the parts to dig in. My initial attack, instead of replacing the whole wiring harness would be to just replace the volume pot assembly first. Everything else is functioning fine, so don't want to got through a total rewire if I don't need to.

It could be a few things, a dirty pot, resistance in a connection, a connector not fully seated, or in a worst case, interaction with the pickups' characteristics. I'm hoping yours still has the original pups, so I could possibly rule that factor out with my replacements.

I've been watching the forum here, and yours is the first mention I've seen that sounds like the same thing I'm having. Wonder what psarkissian would have to say about this - I'd be interested to hear if he's run into it before on units he's had to deal with....

Dave

 

Thank you for describing your similar issue!

 

- I only noticed this on the models; I didn't check the magnetic pickups

- Magnetic pickups are stock in my JTV-69 (HSS)

- This JTV had its wiring ("User Interface" as FC describes it) replaced a few years ago (under warranty) to fix a model knob switch issue

- The volume pot has lately become scratchy/noisy in the typical analog way when running mag pickups through 1/4" jack

- I haven't noticed any issues until yesterday with the models (I rarely use the magnetic pickups)

 

I'm not an EE, but I have a few thoughts:

 

- There must be some kind of "smoothing" with the way the modeling engine interprets the motion of the pots

- The symptoms (slowly "coasting" to a stop, not reaching the endpoints) seem like they must involve that smoothing

- i.e. Either the smoothing goes wrong somehow, or a scratchy pot's erratic voltage changes confuse it

- If part or all of the smoothing is done in the analog domain, it must involve a capacitor

--> I see there's a little tiny cap on the PCB for the volume pot

--> Maybe a fleck of metal debris was shorting it or something

 

Yes I would love to hear if psarkissian has experience with this issue... I bet someone with that kind of knowledge could say "Oh, that sounds like xyz is happening in such-and-such part of the process, so you probably just need to replace this."

[psarkissian]

mdmayfield,...

Might have been the compressed air, maybe was loose creating an

intermittent chassis ground underneath, or both.

 

Debris shorts, yeah I come across those every now and again, on a host

of products from a wide variety of companies.  It can happen.

 

http://line6.com/support/page/kb/_/general-faq/cleaning-pots-and-faders-r816 

 

... other possibility for future reference.

[klangmaler]

So, if you want try something, then use (oil free) compressed air.

Almost every rotary sliding potentiometer is an expendable part,

because it loses smallest amounts of the resistive element (material)...

Avoid using any fluid stuff at all costs.

[mdmayfield]

mdmayfield,...

Might have been the compressed air, maybe was loose creating an

intermittent chassis ground underneath, or both.

 

Debris shorts, yeah I come across those every now and again, on a host

of products from a wide variety of companies.  It can happen.

 

http://line6.com/support/page/kb/_/general-faq/cleaning-pots-and-faders-r816 

 

... other possibility for future reference.

 

 

Thank you for the insight!

[psarkissian]

No problem.