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Brach,
My pedal was working fine until I disconnected the power and then reconnected it. After reconnecting power, it was passing no sound. I usually have the pedal volume at 12:00. Curious, I turned the volume knob up. Just before I reached maximum volume, the pedal began outputting sound again. This was with the tremolo on. It was nice and loud and sounded normal again, but when I started to turn the volume back down, the sound cut out. So, it only outputs sound with the volume almost on full. When I hit the bypass switch, the volume drops and is then almost inaudible even on full. I’m thinking something might have gotten fried when I reconnected the power, but I need some help tracking down what that might be. Do you have any clues?
Thanks,
PeterBy the way. Every other function of the pedal still works fine. The volume control is the only issue.
ThanksI’m almost positive that nothing got fried.
Are you saying that it unusually quiet when the effect circuitry is being bypassed and basically off when the effect is engaged until you crank up the volume?
This is a very common occurrence when there is a bad solder joint in the circuit somewhere. Often times, with bad solder joints, the signal can’t quite get through until the volume is cranked up and the signal has enough power to push through the high resistance of the bad joint. Once it pushes through, it often works for a while (even at lower volumes) but eventually cuts out again. I suggest that you re-flow all the solder joints in the analog part of the circuit, but you might as well do the whole board while you are at it. If there is a bad joint one place, there are likely to be others. When i say “re-flow” what I mean is heating up the joint enough to melt the solder so you can touch the solder wire to it. Not to add more solder, but to add more flux, which is incased in the solder wire. The flux is the stuff that boils and smokes when the solder is heated. It helps the solder flow better and most importantly it seals the joint so oxygen can’t penetrate it and cause it to oxidize. Oxidized joints (aka cold solder joints) become brittle and easily crack.
This is why the physical shape of the solder joint is important…when the joint is jagged or has irregular blobs on it, the flux can’t flow properly around the joint to seal it (mostly due to capillary action). Properly shaped solder joints allow solder to easily flow and settle on the surface of the joint, which protects it from oxidation.Good luck.
-BrachThanks for the tips, Brach. I reflowed all the connections as you recommended. Still, no luck. I also checked all the voltages, and there were two weird readings. I’m only getting .42v at R28, and pin 5 of U2 is only reading 2.4v. Every other reading was normal. BTW, this isn’t the first issue I’ve had. In tracking down a previous issue, I very well could have overheated a component or two. I like to think I can solder decently, but I haven’t worked with printed boards much until this project. IMHO, the design of the pedal and the quality of the components is excellent. I loved the pedal when I had it working, but I’m starting to feel like my board is a lost cause because of all the abuse I’ve put it through. If I can’t track down the issue, would it be possible to get a fresh board and set of caps, resistors, etc.?
Thanks again,
PeterPeter,
At least one problem is with the silencing circuit, with R28. If that pin isn’t high (around 5v) then the output will be silenced. Please make sure the isp header pins aren’t shorted. Also make sure C18 isn’t shorted. See if you are getting 5V on one of the pins of R29, as the schematic indicates. If there are no shorts across any of those pins (checked with a multimeter continuity tester) then temporarily remove C17 to see if the shorting circuit is broken (heat up both pins at the same time while gently lifting it off; then use a solder sucker to clean out the holes). It is possible that the FET could have been damaged.
Don’t worry about the voltage discrepancy on the U2 pin for now.
Unfortunately, we’ve packed up all these circuit boards into kits, so we don’t have any available to sell by themselves. The good news is that circuit boards are very difficult to damage past the point of repair. If traces are broken, you can always run jumper wires in their place. If pads are lifted, you can always run components point to point or connect them with wires. There’s almost always a way to fix circuit boards…the schematic makes it pretty easy to see where everything goes.
Let me know what you find.
-BrachBrach,
R29 reads 5v on one end and 2.5v on the other. There is no continuity across C18. I pulled C17 like you said, and there is continuity across those points. Also, on the ISP, I’m reading continuity across all of those pins, but I’m not sure if I’m testing them the correct way. Should I just be testing all of those pins for continuity to ground? If that’s the case, then no, there are no shorts to ground on the ISP. Do you think that Q3 (J176) is damaged?
Thanks for your help with this.
PeterThat’s exactly what I would expect on R29. Good, there is no continuity across the pins of C18.
So once you pulled C17, did the pedal start working?
Are you testing for continuity with the power on or off?…because it should be off.
If it is true that you are getting continuity across the pins of C17 after it is removed then that is a problem. You must have a solder short across those pins. Please fix it or re-test it for continuity. They should not be connected.
If you are getting continuity between any 2 pins of the ISP header then there are solder shorts across them or something else in that circuit. See the schematic for more details. You must be doing at least one thing wrong because one of the ISP pins should be connected to ground. Please re-test these pins.
The main question is did the pedal start working when you pulled C17? If not, check for continuity across those cap pins…fix it if they are shorted. If it did start working after you pulled the cap, then the fet is probably bad or the ISP header has a short across 2 of it’s pins.
-BrachSo, I finally got back to this. I checked the ISP correctly this time, and there are no shorts between the pins. I pulled C17 and checked that again and there isn’t a short there either. With C17 pulled (and the pads with it #%&@!), the pedal has no output at all. I checked all the cable connections and made sure the volume pot was turned up, but there’s no sound. Voltages still read like before, with .45v on R28. I can read a schematic only basically. I know what all the components are and what they are there to do, but I don’t fully grasp how they all interact together. So, my uneducated belief is that the low voltage on R28 could mean that there is a problem with Q3. It might have an internal short, or something. Could this be true? Would you recommend replacing Q3? I cannot find any problems anywhere else in the silencing circuit.
Anyway, I really do appreciate all your help so far.
Thanks,
PeterOr, wait. With C17 pulled, isn’t the circuit with Q3 totally removed from the loop? So, in that case, could it be a problem with the relay? I’m just shooting in the dark.
That’s correct about C17 being in the same circuit as Q3. So if there are no shorts across the pins of C17 then Q3 is not the main problem. It is still not behaving correctly because of your voltage measurements, but that’s not the thing causing no signal to pass through the board because C17 is removed.
You are right, it could be the relay. Go through steps 5-7 on the troubleshooting guide (assuming it passes all the steps up to that point). If that doesn’t help you may consider following the steps in appendix A to see if the LEDs in the optocouplers are working correctly.
-BrachGoing through step 5 of the TG: There is NO continuity between input/output tips with bypass led OFF. With led ON, there is continuity between input tip and R1. There is NO continuity between output tip and vol. pot center lug. The relay clicks whenever bypass switch is pressed. R28 reads .45v. Everything is installed correctly and solder joints all look good. The pedal worked well for many months until this recent issue. It was never dropped or handled roughly. I’m just assuming it’s a component failure, but finding which one is certainly a challenge!
I hope this info helps.
Thanks againBrach,
BTW, I’m in S. Korea right now, so I’m typing this while it’s late at night (or early in the morning) there in Chicago. Regardless, thanks for your prompt replies.
PeterWow! You are quite a distance away from me right now. The internet has made the world such a small place.
Something might be wrong with your continuity testing. You said you were not getting continuity between the input and output jack tips when the bypass switch is off (which means signal will pass through your pedal when the LED is off)…but in your first post you implied that you were getting signal through the pedal when the bypass switch was pressed (when the LED is turned off), and then when the bypass LED is turned on, the signal drops in volume, unless I read into your post the completely wrong way.
Anyway, this makes me have a hard time trusting that your continuity tests are accurate. Could you please let me know if you are getting signal through your pedal when the bypass LED is off?
-BrachSorry, Brach. I didn’t clarify that in my post from a couple days ago. When I tested the pedal after removing C17, it no longer produced any sound at all. The symptoms that I described in my first post have totally changed. There is zero output from the pedal now in either bypass or normal mode. That explains the lack of tip to tip continuity in bypass. That also makes me assume the relay is the problem. But if that’s the case, do you think it was also causing the original issue?
Thanks,
PeterBTW, my good meter is broken, so I’m testing for continuity with my cheap old Radio Shack meter that doesn’t have a dedicated continuity test setting. So, I’m testing using the lowest Ohm setting. I need to get a new meter…
Are you making these tests while the pedal power is off or on?
In your re-flowing the solder joints something must have changed…most likely something was shorted. Make sure that the pins of C17 aren’t shorted. You may just want to try it out with a guitar to see if signal isn’t making it’s way through while the effect circuitry is bypassed.
It seems like there may be several different issues that are causing these problems (or possibly inconsistent/intermittent test results). In cases like this we need to eliminate each potential issue in hierarchical order. The issue at the top of the list is your meter. You probably should wait until you get a trustworthy meter that can give you good results before you continue. I’ve used a few old radio shack meters before and from my experience they aren’t very reliable.
-Brach
