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That does seem strange….double check to make sure you are really testing the correct pins.
Also, check for continuity between pin 23 and the center pin of the depth pot. If the center pin of the depth pot is changing, pin 23 should be changing too, unless that connection is broken somehow.
You also may want to use a ground point on the PCB…like the point where the grounding wire is soldered…just in case the ground lug isn’t making good connection with the chassis.
-BrachThere is a way to do that. It involves disassembling the pedal to get to the spring tension washers on the axle. From there, those washers just need to be re-bent to add more tension to the treadle. I’m actually working on a VPM-1 troubleshooting guide that will have instructions on how to do this…with pictures. But being that we are in pandemic mode currently, i don’t know when i’ll be able to get it done.
Just letting you know something is in the works.
-BrachRobert,
I’m glad to hear the installation went well and the VPM-1 works great for you.
Using a tablet is a great idea. Yes, I’m sure black and white prints are not as helpful….it’s also a lot of paper.
Thanks for the post.
Take care.
-BrachIs the voltage on pin 23 changing as you turn the depth knob? It should be connected to the center pin of the depth knob. Make sure your meter’s probe isn’t touching any other pins on the micro when you are testing pin 23.
-BrachNicholas,
Unfortunately, this sounds like the microcontroller may have been damaged. But when you measure the resistance between pin 4 on the micro and the round pad of “Tap sw”, you get 1.5 what? What units? What about when you measure the continuity between pin 4 of the micro and the square pad of the “tap sw”…are they connected?
-BrachGrady,
That doesn’t sound like the microcontroller to me. If it was the microcontroller, you’d have more problems…the other features wouldn’t be working properly….but i may be wrong. To me, it seems like a bad solder joint somewhere. Start by re-flowing the solder joints on the depth knob. But just for good measure check to see what voltage you get on the center pin of the depth pot (or pin 23 of the micro)…you should be getting from 0v to 5v as you turn it up (from counter clockwise). Also make sure the micro is seated in it’s socket very well.Thanks for the question.
We designed the chassis on the VPM-1 to fit on the VP Jr line of Ernie Ball pedals. Unfortunately it won’t easily screw into the bigger original line of Ernie Ball volume pedals…the hole spacing is a little off. It probably would be possible to drill a hole through the aluminum volume pedal chassis to accommodate the VPM-1 chassis, but it might be tricky because you’d have to drill through part of the “counter sink” (or chamfer) of the original hole.
I just tested the electronics on the the original EB that i have laying around and everything seems to work well. The magnet lines up nicely to the sensor board.
One thing that i noticed was that when i took the string off the pedal flopped around and didn’t stay in one set position. So i took the treadle/axle mechanism apart and noticed that i didn’t have the spring disc washers that the VP Jr pedals have to keep the treadle tight. I ordered some of these spring washers so hopefully that will fix the loose treadle. This is the only classic EB volume pedal that I took apart so i’m not sure if it’s normal for them to not have the spring washers…apparently it was for that production run.
So to answer your question, if we there’s enough interest in the VPM-1 for the classic EB volume pedal, we’ll look into starting a production run with a new chassis and face label (keeping the rest of the design the same). But we might have to offer these spring washers and instruction on how to mod that part of the pedal too.
-BrachAlright. I understand the frustration and needing to take a break. It can be very confusing working on the solder side of the board where nothing is labeled. But I do think we are close to figuring this thing out. When you are available to look at it again start by checking over the signal path from R15 to pin 3.
Take care.
-BrachOk good, that must be where the problem is. Test for continuity across switch 3 on S5 to see if the problem is with that component or if it is open somewhere else…i’m assuming only switch 3 is on currently. If the pins of switch 3 on S5 are not connected flip on switch 4 or 2 just to see if you can get signal through the LPF. You may have to re-adjust the low side trim pot.
EDIT…i just re-read your post and it seems like you tested across the switch already. If so, test from R15 to R21/22/23/24…it should be connected. Then measure the resistance across R22 to see if it is really 18K. Then test across the switch (switch 3 should be the only one connected, do it again for good measure). Then test to see if the other side of S5 (the opposite side from the resistors) is connected to pin 3 of U2. …just figuring out where in that signal path it’s not getting through. My guess is S5 because that’s the only component with moving parts.You can test if the LDR is working by unsoldering the jumpers (JP3 and JP4) and measuring the resistance across TP3 and TP4. Keep the depth knob off and the resistance should be relatively low (when the power is on). But you should have already done this when you calibrated the pedal, so I would guess that it’s still working.
When you measure the resistance between R15 (the pin of R15 closest to pin 1 of U2) and pin 3 on U2, what do you get (with the power off)?…I’m wondering if S5 is working properly.
Also, what DC voltages do you get on the pins of U2A, pins 1,2, and 3?The problem seems to be with your bias voltage (called V/2 in the schematic). Pin 10 is directly connected to V/2 and you measured that voltage to be 0V, it should be half of the power supply voltage (9V/2)…around 4.5V. You can see the bias network in the center of the page on the schematic…it’s a voltage divider consisting of R10 and R9, along with C15, C10, C11, and C16. Make sure the pins of C15 aren’t bridged. Also make sure none of the other pins are bridged to anything and everything is soldered correctly.
-BrachThat was quick.
So that tells us that the digital side of things is working properly, so we know the issue is with the analog circuit.
When you turn the gain trimpot up all the way (counter clockwise) do you notice the LFO noise getting louder? I’m just trying to see if that component/part of the circuit is working properly.
It would also be helpful to know the DC voltages of all 14 pins on the TL074, with the depth knob all the way down and no audio signal in the input jack.
By the way, do you hear the relay click when you press the bypass foot switch?
Thanks and good luck.
I probably won’t be able to respond more until tomorrow or monday.
-BrachOk, good.
Now check to see if the LEDs in each optocoupler are working by making a tiny incision on the heat shrink close to the LED’s leads….just a tiny cut, no bigger than 1mm long…just enough to see if the LED is working.
Let me know what you find.
-BrachI just have to ask…are the jumpers soldered properly? Sometimes people accidentally skip that step, or just solder them wrong.
Another thing i wanted to make sure of…are you able to tap out a rhythm on the tap foot switch? …Just to make sure the microcontroller is working properly.
The faint pulsing you hear is probably just the LFO leaking through to the audio or ground path. It’s normal when the volume is all the way up.
Let me know about the jumpers.
