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Sebastian,
I’m sorry about this late reply. The last 2 days were very busy and hectic around here.
Thanks for answering my previous questions. I’m going to assume that your LDR pair is matched (because we matched them when we assembled your kit) so the issue has to be that the LED is not getting bright enough to cause the LDR to lower it’s resistance to a reasonable value.-Check everything in the circuit between the microcontroller pwm output and the LED. They are: Q1, VR8, and R8.
-Check to make sure the solder joints on these components are good and there are no shorts between any of their solder pads.
-Check to make sure all these components are correct values.
-Make sure R8 is getting 5V on the correct pin (as shown in the trouble shooting guide) and compare the voltage of the other pin on R8 to the same pin on R7.
-Test to make sure the trim pot is working by measuring it’s resistance….from the middle pin to the one of the side pins. Then turn the trim pot about 10 or 12 full turns and re-measure the same pins.
-You should also compare the optocoupler LED voltage (as in the trouble shooting guide…the yellow pads in the voltage chart)…both of them should be around 1.8V.Look into all that stuff and let me know what you find.
Good luck!
-BrachMike,
Sorry about the tuner trouble.
Was the tuner output working on your previous pedal board setup?
Do you have the expression mod installed on your VPM-1?
-BrachSebastian,
Pin 5 of U2 is fine with that voltage.
I think you may be mistaken by the role of VR8…notice the schematic. VR8 limits the voltage of the LED on the high side optocoupler, while TP1/TP2 are connected to the high side LDR. So this makes me wonder if the solder jumpers are already soldered when you are making this measurement. If so, unsolder them and re-calibrate the trimpots. Let me know if this was or wasn’t the issue…it’s important for me to rule this out when deciding what we should do next.
-BrachJefferson,
This is almost certainly related to bad connections (ie solder joints) within the circuit. The fact that it is behaving differently even though nothing external has changed indicates to me that something internal has changed…like some connections are intermittent. Please make sure the paper insulation has not been punctured and nothing is shorting to the back of the pots. I suggest reflowing the solder joints (all of them) to ensure that they are all working properly. If you haven’t soldered many projects yet, make sure your iron is getting hot enough and you are using the proper amount of solder on each joint…it’s easy for joints to be bad if there isn’t enough solder on them.
Good luck!
-BrachThat’s my fault! I’m so sorry, I told you the wrong pin to solder the wire to….it supposed to be pin 4, not 3. I’m so sorry! I was going from memory yesterday when I told you the wrong pin, but after reviewing the schematic I realize that pin 3 is the bypass pin.
The good news is that you don’t need to solder to pin 4 on the microcontroller, if you don’t want to…there is a little via (a little hole through the board) right below R16 (10K resistor) that you can solder the wire to. That may be easier than soldering to the IC pin, but maybe not, now that you have some practice doing that. If you are wondering which via it is, it should be connected to pin 4…just use your continuity tester on your meter to test it.
Good luck and sorry for the bad information yesterday.
-BrachYes, there is always a way to bypass pads by running jumper wires. If the square pad is damaged then run a jumper from one of the switch lugs (either one is fine) to any of the ground pads around the board.
If the round pad is damaged then run a jumper from the other switch lug to pin 3 of the microcontroller. Just tack the wire to the top of the pin close to the body of the IC. Remember to tin the wire and pin first. And only use just enough solder that you need, it’s easy to over do it and bridge the IC pins together. Otherwise, you can always remove the board from the chassis and attach the jumper to pin 3 on the solder side of the board.
Good luck!
-BrachThanks for the thoughts, Dirk.
It will probably be a little while before we decide about creating a new line of mods for the bigger pedals. I may end up creating a tutorial on how to mod the bigger version with our current mod. Like i said, the mod works really well when it’s installed, it’s just a little annoying to install.
Anyway, thanks for the comments.
-BrachRiff Man J,
That’s a very interesting problem to have. To me, it seems like the pot may have some dead or dirty spots on the carbon track that’s bringing the voltage down to 0 volts at those points. You can check this with your voltmeter. Test the voltage of the center pin of the pot when the wiper is on those dead spots. The center pin should have a continuous voltage from 0v to 5v as you sweep the pot from one side to the other. If the voltage drops to 0v on those spots then the pot needs to be cleaned or replaced. If the voltage is continuous all the way across the sweep of the pot then the problem has to be software related.
Let me know what you find.
-BrachChris,
If you don’t feel confident running the jumper wire then it is probably wise to get help from someone local to you. If you have any friends that have done any electronics soldering, I would ask them. Otherwise you can take it to an electronics repair shop and they should be able to fix it.
Good luck!
-BrachI’m sorry you are having this trouble.
Are you saying the LED on the optocoupler is not working?
Were you able to test the LED with your meter, as described in section iv of Appendix A?
-BrachThank you for the photo. You can still make it work.
The main problem I see in the photo is that the copper trace from one pad of the opto1 to TP1 is ripped off. You need to install the optocoupler again and then run a jumper wire from that pin of the optocoupler to the hole of TP1. Don’t try to solder to that pad of the optocoupler because it has been damaged and probably won’t accept solder or pass an electrical connection. You need to use a tiny wire for this jumper…something you would find inside of a USB cable or DVI video cable or something like that. See Appendix C in the troubleshooting guide for more about how to run a jumper wire.
Once the optocoupler and jumper wire are installed, work through Appendix A of the troubleshooting guide. This will help you decide what is wrong with the “high” side. If you don’t understand any of the steps, let me know and i’ll try to walk you through it. These problems usually are caused by bad solder joints. So please re-solder any of the joints that are around that area…especially: Q1, R14, VR8, and R8.
Good luck!
-BrachAt what step did you get stopped? Were you able to make it to step 4?
Were you able to calibrate the high trim pot before you soldered the jumpers?Chris,
Thanks for the kind words about the Quaverato.
To give the Quaverato “deeper” depth you can increase both tone trim pots the same number of turns to get their individual signals louder (turn them clockwise). Just make sure you increase the same number of turns on each pot to keep the same hi-to-low ratio. You may have to turn down the gain trim pot to make up for the increased volume.
Another thing you can do is to make sure there is no light getting into the optocouplers. Make sure there are no tiny holes in heat shrink (from the soldering iron shrinking the tube), especially on the LED side. I often use opaque black hot glue to cover the ends to ensure no light gets in.
Also, make sure you keep the harmonic mix knob at 12:00…make sure your knob is attached to the proper location on the pot otherwise what you think is 12:00 might not be.
Generally, the slower the LFO, the more pronounced the phasing effect will be. This is because the LDRs have a finite time it takes them to go back up to a high resistance after the LED has turned off. Slower LFO rates give the LDRs time to fully recover to their “off” resistance.
I hope this helps.
Good luck!
-Brach
