Currently Being ModeratedAug 14, 2012 3:22 PM (in response to RainmanRam)Re: Spank models not coming on.
The knob is a potentiometer and the circuit reads the resistance value to determine which model to select.
In the old Variax 500/700 there was a knob calibration procedure, but that was taken out of the 300s and 600s. I don't know of a knob calibration procedure for the JTV.
Here's a couple of things you can try.
First, rotate the selector knob it's full range of movement about a dozen times. What this does is it will clean away any muck (usually caused by condensation and dust) out of the pot that might be giving an incorect resistance value. Give that a go first because this is a simple solution that often works.
Second is a tip that came from 1oldguitarman and it involves making sure the middle position of the pot corresponds with the middle position on the selector knob. Personally, I don't think this will help you because if this is the problem you'd be more likely to have an incorrect reading on Custom 1 and Model T as well as Spank, but if the above doesn't help and you're technically minded, this might help you. The instructions relate to the original Variax and I have no idea how the knob is seated on the pot in the JTV, so while the aim of the procedure is sound, the actual procedure may be quite different on the JTV. Anyway, here's how to "Split the Difference" on the selector pot.
PLEASE NOTE: The following procedure will only work if the selector knob has be calibrated around the centre position of the pot, if it hasn't then the following procedure will make the problem worse. This procedure was designed to improve the calibration process and assumes that you can actually calibrate the knob after completing the procedure.
"SPLIT THE DIFFERENCE": the model select potentiometer has more travel than the physical detent knob allows. You can observe this by turning the selector to CUSTOM 1 (fully counter-clockwise), then very carefully removing the knob entirely from the stem of the pot while not allowing any pot rotation. The pot can probably turn further CCW. If not, place the Model Select back onto the stem, turn fully CW to CUSTOM 2 and pull the knob off. You'll observe extra travel. UNTIL I ROUGHLY SPLIT THE "EXTRA" ROTATION DISTANCE BETWEEN CUSTOM 1 (fully counterclockwise) AND CUSTOM 2 (fully clockwise), the calibration procedure failed repeatedly for both of my VAXes. The procedure resulted, sometimes, in different model selections being missed, but always a model selection would be ignored/missed.
To SPLIT THE DIFFERENCE:
- Turn Model Select to CUSTOM 1
- Carefully pull (remove) the knob from of the stem of the potentiometer
- Turn the pot fully CCW
- Place the Model Select knob back onto the stem, making sure it's indicating CUSTOM 1
- Turn the knob fully CW to CUSTOM 2
- Again, carefully remove the knob from the stem, causing no stem rotation
- Note how much extra travel the stem can turn to fully CW (you can place a post-it note or piece of tape at the base of the pot and mark the 2 positions, but I simply eye-balled it and got good results)
- Now, turn the pot CCW, HALFWAY back to its original spot (where it was when you removed the knob at CUSTOM 2 in Step 6)
- Carefully place the Model Select knob back onto the stem, making sure you don't rotate the stem any and it shows CUSTOM 2
Let us know how it goes for you.
Currently Being ModeratedAug 15, 2012 8:52 AM (in response to Crusty_Old_Rocker)Re: Spank models not coming on.
It was indeed a dirty selector knob. I rotated it dozens of times and didn't get it fixed so I took the battery out and sprayed it with some contact cleaner and rotated it a couple dozen more times and it still wasn't fixed so I started on the calibration proceedure even though I agree with you that it wasn't likely the culprit since custom1 and T-model would likely have problems as well.
To my surprise, the knob does not act like a pot and will continuously turn in either direction without ever stopping so I'm assuming it is digital in some way. Nevertheless, rotating it enough times in one direction seemed to do the trick and I now have all my models back.
Currently Being ModeratedAug 15, 2012 3:09 PM (in response to RainmanRam)Re: Spank models not coming on.
Ah, thanks for that feedback. That's enlightening.
Often any misreading by encoders on the Line 6 gear can be attributed to a dirty pot. It doesn't take much to send a wrong resistance value to the processors.
Music gear that's used in an air conditioned environment and then moved to a warmer, humid environment (out in the truck after the show) can introduce some condensation inside and that can be the start of the problem.
I'm glad the information based on the original Variax was helpful.