Boss TU-2 problem.

[BDuguay]

I realized today that most of my posts are requests for help in repairing pedals, and not so much about d.i.y-ing pedals. If this bothers anyone please let me know. I certainly appreciate all of the help I have received in the past and hope I haven't over stayed my welcome so to speak. I am learning a lot and rest assured, I will not ask the same question twice after I get the answer.
Now, I have this Boss TU-2 that works fine except that it does not mute the signal when engaged. The signal gets reduced a little but not completely muted as it should.
Fortunately, I have another properly functioning TU-2 that I can use for reference but I'd like to know where to start troubleshooting if anyone has any suggestions.
Thanks as always
B.

[EARNEST]

Did you drop it? Hit it? Check all the cables, connections, leads, clips etc.

[Processaurus]

Something is amiss with the FET switching that boss uses for all their pedals, though it may be a different arrangement than the others as it probably just uses a FET to shunt the signal to ground to mute it, after the input signal splits off through a buffer towards the normal and bypass jacks.  I imagine something like the mute on the NS-2 schematic, as boss reuses many of their circuit elements. Q5 in this schematic :
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/NS2small.jpg.html?g2_imageViewsIndex=1

I've never seen a TU-2 schematic, if you can find one, it would be much easier to diagnose.

[ayayay!]

Forgive me if I'm wrong, but isn't there a jack that allows you to keep the signal engaged while tuning?  I thought the TU-2 had that option.  Are you plugged into the wrong output jack? 

[BDuguay]

Forgive me if I'm wrong, but isn't there a jack that allows you to keep the signal engaged while tuning?  I thought the TU-2 had that option.  Are you plugged into the wrong output jack? 

I probably should have mentioned that, sorry. Yes, I'm aware of the functions of the 2 outputs. The bypass out works fine but the 'Output' out is the one to use for silent tuning and it's only partially muting the signal.
Thanks for the tip Processaurus, I own an NS-2 so I can examine it against the the Tuner to see if there is a resemblence in the topology. That should keep me busy.
I shall report my findings.....
Thanks again everyone!
B.

[earthtonesaudio]

Seems possible that only one side of the bypass is malfunctioning.  I'd say audio probe it to figure out which JFET switch is "stuck open."

[BDuguay]

I gots me one of them audio probes. I'm a little embarassed to admit  I'm not sure how to use it for troubleshooting like you've suggested
B.

[earthtonesaudio]

Follow the normal debugging procedures first (always).

Plus:
Verify the LED is working (pressing the footswitch switch causes the LED to change state).
Then measure the voltages on all 3 terminals of all the JFETs, when the effect is engaged, and when it's bypassed.

This info may be enough to determine the source of the problem, but if not, be prepared to:
Use the audio probe on all terminals of all JFETs, starting with the one closest (electrically) to the output that should be muting (but isn't).
Note the difference between bypassed and engaged.  One terminal of each JFET should become dramatically quiet in one position and pass sound normally in the other position.

[BDuguay]

Yup, the staus LED is functioning correctly.
Thanks again.
B.

[BDuguay]

It's working proper now, and I don't know how I fixed it.
I had another TU-2 that I used for comparison and found some discrepencies in voltage readings on some of the FET's. Some of the eletrolytics on the troubled TU-2 were all bent over and I suspect some of their leads were touching things should'nt cuz after straightening the problem was solved.
B.

[rockerbip]

Please drop a donation like I did !
http://www.synfo.nl/servicemanuals/Boss/TU-2_SERVICE_NOTES.pdf
Cheers

Marco