Home › Forums › Quaverato Forum › Quaverato FAQ & Support › Quaverato works great… except the rate knob
- This topic has 10 replies, 2 voices, and was last updated 1 year, 5 months ago by brach.
Hello all. The Quaverato is my first ZDL build, but certainly not my first build. I’ve probably built 10 to 12 pedals over the last few years.
I finished my Quaverato build last night and powered everything up to test. It seems that everything works EXCEPT the RATE knob. The other 6 knobs work as do both the switches and all LEDs. If I tap in a tempo, the rate LED changes but nothing happens when I turn the rate knob. I checked the troubleshooting guide and I don’t see this issue listed. It was getting late, so I went to bed and figured I’d have a look tomorrow (today).
Today, I checked it again and sure enough… no response on the rate knob. I went into calibration mode… both sides check out. Metered all the voltage points (from the troubleshooting guide)… they all match. I took the pedal back apart and re-flowed the joints on the rate pot… no change. I put on my magnifying glasses and inspected all the joints… they all look good (I realize you can’t always see a cold joint but still). Everything else seems to work fine.
I know it’s frustrating to get done with a pedal and discover that one thing isn’t working right. Sorry for your frustration.
You said that the tap time is working, correct? If the tap footswitch is working correctly then the issue probably is on the analog side of things…meaning an issue with the voltage getting from the rate pot to the microcontroller. On the schematic you can see that the center lug of the rate pot (VR2) is going to pin 24 of the microcontroller. So test that with your continuity tester (with the pedal’s power off). Test it with the meter probe on pin 24 right as it exits the microcontroller’s body, not the solder joint because there could be an issue with socket. If that’s good then power the pedal on and measure the voltage on that pin as you rotate the rate knob. The DC voltage should scale from around 0 volts to around 5 volts as you rotate the knob. If you have trouble with these tests check the solder joints around pin 24 for shorts or opens. You can also test that the left and right rate pot pins are connected to ground and the 5V rail.
Do these tests and let me know what you find.
That’s correct Brach. The tap tempo works perfectly. Your reply sounds like great advice. Thank you for the insight. I’ll take the pedal apart and check these things tomorrow.
Brach, thank you again for the great troubleshooting advice. I was able to test the pedal today. Here’s what I found…
-Center pin of rate pot to pin 24 on IC is a good connection (metering at the IC itself)
-Rate pot has good 5V (4.98 to be exact) current on right (based on bottom view) lug
-Rate pot has solid ground on left lug
-Center lug of rate pot is metering 4.98V regardless of the position of the wiper (unless you turn it all the way counterclockwise and then it meters 0V)
Basically, the rate pot passes 0V when fully counterclockwise. As you turn it slightly clockwise, it jumps to 5V and stay there for the rest of the wipe.
It sounds to me like I may have a defective pot but I’d like to hear you’re opinion.
You possibly have a bad pot, but there’s also a good chance that the problem is something else, like the microcontroller is injecting 5V on the pot…you just don’t notice it until there is enough resistance on the pot to hold it above ground level.
Test the pot by measuring the resistance of the microcontroller’s pin 24 to ground, when the pedal power is off. It should scale from around 0 ohms to around 100k ohms as you turn it. If it’s is stuck at some high value for most of the rotation then the pot’s bad.
If the pot’s good then remove the microcontroller from it’s socket (very carefully, without bending it’s pins) and power up the pedal…then measure the voltage on pin 24 again as you rotate the rate pot. Test to see if the voltage is scaling as you rotate it. If this works, then the problem is with the microcontroller…or there’s somehow a short between pin 24 and 5V.
Let me know what you find.
I love the way you think Brach. Great suggestion and I have some more findings.
With the power off, I metered from pin 24 of the IC to ground and swept the rate knob. I found the values ranged from 0 Ω to 3.28 KΩ (that’s not a typo… I attached a pic – it’s a little difficult to see the small K in the lower left of the screen but it’s there). I also metered directly on the center lug of the rate pot to ground and I’m getting the same range – 0 Ω to 3.28 KΩ.
I stopped troubleshooting there and didn’t bother removing the IC. I believe this tells us the circuit is solid from the pot to the IC and the pot is probably our culprit but I’d love to hear your analysis as you seem to have a great understanding of this circuit. Again… thank you so much.
Thank you for making that check. You may very well be right about the pot…But i do think you need to take the microcontroller out and test it again without it in the circuit. What if the microcontroller has an internal short or partial short to ground?…you could get the same test result. Testing components in a circuit can be kind of tricky because you have to consider everything else that is attached to that circuit node. The microcontroller pins are supposed to be high impedance (over 1M) but it is possible for each pin’s internal resistor to become damaged. I’m sorry I mislead you in my previous directions, I forgot about this contingency. And sorry to have you keep working on this, but it’s important to get an accurate diagnosis.
Let me know what you find.
Again… great insight Brach and thank you for all your help.
I pulled the microcontroller with my IC puller (side note… all pins are nice and straight). Then I powered up the pedal and metered pin24 to ground while turning the rate knob.
When the rate knob is fully counterclockwise, I’m seeing 0.19V at the IC socket. Then as I turn the knob clockwise, I see small scaling increase until I hit about 1/8 travel. At that point, it jumps to 4.98V and remains there for the rest of the wipe. To clarify, I’m seeing 4.98V for about 7/8 of the pot’s sweep.
Good job! Now we can be (mostly) sure that your pot is not working correctly. Once you remove it, just double check the resistance (from the center lug to one of the side lugs) as you turn it. Technically, there still is a very small possibility that there is a short on the center lug from some other 5 volt point, but practically we have enough information to warrant you removing the pot from the board. Once you do this final test on the removed pot and find out that it’s bad, email us at info “at” zeppelindesignlabs “dot” com and give us your address and serial number so we can send you a new part.
Thanks again for the excellent suggestion Brach. I went to desolder the pot from the board and noticed something I hadn’t before. The manual has us tack the pots in place on the top and then solder them on the bottom. Well, the tack on the center pin of the rate pot had a “tail” coming off of it and it was dangerously close to R29. I think you can see where this is going… I got out the desoldering braid… slurped the excess solder up and guess what… the rate knob works perfectly.
Ugh. I guess the sloppy solder was close enough that it was involving R29 in the circuit and thus why the knob was metering so wonky. I’ve now re-tested everything with the meter (and with audio) and it seems like the pedal is working flawlessly. The only thing I haven’t tested yet is MIDI. I’ll do that later.
Anyway… I am so sorry… I don’t know how that happened but obviously I got sloppy on that one tack. FWIW, I double-checked all the rest of the pots and they’re all clean. I’m sorry for making you work so hard to diagnose my sloppy soldering. I am really embarrassed.
Regardless… I can’t tell you how much I appreciate your help even if it was my mistake all along.
Well that’s good news! There was a small chance of something like that happening, so good job finding it. I’m glad I was able to help you. It’s fun to practice my troubleshooting skills. And troubleshooting remotely helps keep my skills sharp!
Anyway, enjoy your Quaverato!