I have a Boss BD-2 pedal that i got for free but it isn't working. I'm pretty new in circuit design so i was hoping someone might be able to help me out. At first i noticed two bad capacitors that were bulging pretty bad so i replaced those (C3 and C4 on the link), but that didnt fix the problem. Can anyone help me out? I can post pictures of the actual PCB if that helps. Thanks🙂
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/bossbd2.gif
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/bossbd2.gif
Your link doesn't work.
I don't know what the two caps do, but the most common cause of such issues in a repair shop is that someone plugged the wrong power adaptor into the pedal. On a Boss pedal that usually takes out a protective diode by the corner. But in general, look first for failed parts in the power supply. Things that would be harmed by reverse polarity in particular.
I don't know what the two caps do, but the most common cause of such issues in a repair shop is that someone plugged the wrong power adaptor into the pedal. On a Boss pedal that usually takes out a protective diode by the corner. But in general, look first for failed parts in the power supply. Things that would be harmed by reverse polarity in particular.
Sorry, this one should: The Free Information Society - Boss BD2 Electronic Circuit Schematic
If not its the first google image option if you search for the schematic.
Thanks for the reply. Could you give me any more info? Like which diode and what damage to look for. Thanks so much!
If not its the first google image option if you search for the schematic.
Thanks for the reply. Could you give me any more info? Like which diode and what damage to look for. Thanks so much!
Lower left in the schematic, that is where the power comes in. C3 and C4 blown up is consistent with bad power applied, probably reverse polarity or AC. Protective diode is D2 right next to C3. Is it shorted? If C4 blew up, there is a good chance Q2 is also bad.
I actually checked d2 before you replied after figuring out that is the polarity protection diode. (I believe so at least) It was blown. What do I need to replace that with? How would I check Q2? Also I figured I should mention that there's no sound output even when it's off. Does this mean that the AC damaged the audio side of things in the pedal? Thank you so much for responding to me.
The VERY first thing to do when debugging something like this is to check the voltes. See down at the bottom left of the schematic, there are some voltages given. Check that those are present and within say, 10% of the specified voltage. Nothing is going to work at all without power, so check it.
After that once you know there is good power on all the voltages then you put a signal into the input and trace it stage by stage. Check right at the input jack first and follow it to the output. At some place you will find no signal.
You WILL need some test equipment. No one can see electric signals in wire, a voltmeter that can measure AC and DC volts down to a few millivolts is about all you really need. A 'scope makes it easier but you don't need one. You will also need something to put a signal on the input. You could use a guitar but a constant sine wave make it easier.
Yep, good advice.
D2 is just a diode, I'd use a 1N4007 from my drawer.
Remove a shorted D2, and replace C3, C4, then Q2 has three legs, no two should be shorted together. check all three combinations.
Most meters today include a "diode test" function. it is also used for a rudimentary transistor test. Google up testing transistors with a meter.
Then try it and see if your voltages are close to the drawing. How about with a battery?
D2 is just a diode, I'd use a 1N4007 from my drawer.
Remove a shorted D2, and replace C3, C4, then Q2 has three legs, no two should be shorted together. check all three combinations.
Most meters today include a "diode test" function. it is also used for a rudimentary transistor test. Google up testing transistors with a meter.
Then try it and see if your voltages are close to the drawing. How about with a battery?
Thanks for helping me out Chris. I understand testing individual components like diodes and what not, but i'm a little confused on testing the voltes. Where exactly would I test for those voltages? Also, how do i trace the input signal? Sorry, I'm very new to all this and have a lot of work and reading up to do. Thank you guys so much again for the help.😀
Unless otherwise listed, voltage readings on a schematic are taken with respect to ground. So connect the black probe from your meter to ground in the pedal, and then probe the points in the circuit with the red probe.
Usually the case of a pedal is ground. I usually clip my wire onto the shell of a plug in one of the jacks as ground.
Having done that, do you get more or les 9vDC at the top of D2 and C3? And about 8v after the transistor? And so on.
Usually the case of a pedal is ground. I usually clip my wire onto the shell of a plug in one of the jacks as ground.
Having done that, do you get more or les 9vDC at the top of D2 and C3? And about 8v after the transistor? And so on.
Thanks Enzo!! I'll get to that tomorrow. Also, I don't have any 1N4007 diodes. I'm waiting on some to be delivered. I do have some 1N4005s though. Do I need to wait on the 1000V instead of 600? How could I tell? Would it be a bad idea to try it? I really can't thank you guys enough for all the help.
1N400x...anything is fine. This pedal works on 9v, I don't think the diodes come any lower than 50v. I said 1N4007 because I don't stock the lower voltages. A 1N4007 works anywhere the lower voltage ones work, but the lower voltage ones won't always work where the 1N4007 goes, y'see? Most any generic 1A diode.
It is just a diode. If proper polarity voltage is fed to the circuit, that diode does nothing, it sits there. If reverse polarity voltage is fed to the circuit, that diode shunts it off to ground. It usually gives its life in the process, but it also usually protects the pedal from much further damage. Not always, but...
It is just a diode. If proper polarity voltage is fed to the circuit, that diode does nothing, it sits there. If reverse polarity voltage is fed to the circuit, that diode shunts it off to ground. It usually gives its life in the process, but it also usually protects the pedal from much further damage. Not always, but...
Okay, upon closer inspection of D2 i found that it was a 1N4004, so i replaced that. I've replaced D2 C3 and C4. Do i need to remove Q2 from the circuit to test it?
I tested Q2. With red on the first lead (moving left to right) and black on the second, it measured 1.2 V. Same with the Black on the third. When I put black and red on 2 and 3 (in any order) it measures .1 V, but there is nothing when black is on 1 and red is on 2 or 3. I'm not an electronics genius, but I believe that lead 1 is the base and 2 and 3 are the collector and emitter. Since there is current between the two opposite diodes, there must be a short somewhere, so i probably should replace it, correct?
If this transistor is the common shape - round plastic with one flat side - it is what we call a TO92. The schematic calls for a 2SCxxxx that I cannot quite read. But that is enough to tell me it is NPN, and that it is an Asian number. Asian TO92 transistors have this pinout (leg arrangement): Looking at the flat side (where the number is printed) with legs pointing down, the leads are left to right, emitter, collector, base.
The symbol on the schematic has the legs numbered. If we consider 1-2-3 as left to right, the symbol agrees with my description. SO on the drawing, the emitter is to the right, the collector to the left, and the base is on the bottom.
You are testing the transistor with your meter diode function, which is good, but we also must consider the circuit it is in. SO while you got only 0.1v between 2 and 3 (which is collector and base), there is also that 2.2k resistor connected between the pins. SO you could flip your meter to resistance and see if you get about 2200 ohms.
But here is what I think I'd do. I'd plug a battery into the pedal, and a plug into the input jack to turn the thing on, then measure voltage to ground at C3 and at C5. Or if you prefer, at pins 2 and 3 of Q2, which is the same thing. Do you get about 9v at C3? And about a volt less at C5?
The whole circuit runs on that 8v at C5. The 9v is used only for the LED and the switching.
The symbol on the schematic has the legs numbered. If we consider 1-2-3 as left to right, the symbol agrees with my description. SO on the drawing, the emitter is to the right, the collector to the left, and the base is on the bottom.
You are testing the transistor with your meter diode function, which is good, but we also must consider the circuit it is in. SO while you got only 0.1v between 2 and 3 (which is collector and base), there is also that 2.2k resistor connected between the pins. SO you could flip your meter to resistance and see if you get about 2200 ohms.
But here is what I think I'd do. I'd plug a battery into the pedal, and a plug into the input jack to turn the thing on, then measure voltage to ground at C3 and at C5. Or if you prefer, at pins 2 and 3 of Q2, which is the same thing. Do you get about 9v at C3? And about a volt less at C5?
The whole circuit runs on that 8v at C5. The 9v is used only for the LED and the switching.
I'm not getting any power. I tried a 9v battery and a 9v power supply (with the correct polarity). I made sure and had the input and outputs both plugged in. Tested the top of of D2, C3, C5, Q2, etc... and get nothing. What am I looking at now?
I'm also not sure if I'm testing these correctly. I have my multimeter set to Voltage, I have my red lead at the point that im testing, and the black lead on the casing. How do I know for sure what the ground is? The symbol is a chassis ground but im not sure if im doing it correctly.
The top of D2 comes right from the power source. Where are you grounding your meter? I use the shell of the input plug myself.
The negative end of the battery is grounded by the input jack, leaving the positive end to go through the adaptor jack to D2. Using an adaptor, the negative side of it - the center - is also grounded by the input jack, and the positive through the power jack to D2.
If you get no voltage in the circuit, and assuming the battery and adaptor are good. then you have a missing connection or faulty power jack. Track it down. With no power or battery, plug something into the input. Now measure resistance from the ground to the negative terminal of the battery snap. Remember, negative on a 9v battery is the large terminal, so the negative on the snap is the small one. Is there a good ground path from that snap terminal? If not, look for wire broken off the jack or a sprung contact in the jack.
If that works, then stick a battery in it and follow DC voltage. Ground the meter to the shell of the input jack, and with the red probe go tight to the + terminal of the battery. Is there +9v from there to ground? The red wire from the battery snap should be +9, and should solder to TP1 on the board. 9v there? Now look at the three terminals on the power jack, is 9v on one of them? Is 9v on the other one? At this point we should see +9 on the two power jack terminals that do not go to the center pin.
And look closely at the solder on the power jack, it could be cracked.
The negative end of the battery is grounded by the input jack, leaving the positive end to go through the adaptor jack to D2. Using an adaptor, the negative side of it - the center - is also grounded by the input jack, and the positive through the power jack to D2.
If you get no voltage in the circuit, and assuming the battery and adaptor are good. then you have a missing connection or faulty power jack. Track it down. With no power or battery, plug something into the input. Now measure resistance from the ground to the negative terminal of the battery snap. Remember, negative on a 9v battery is the large terminal, so the negative on the snap is the small one. Is there a good ground path from that snap terminal? If not, look for wire broken off the jack or a sprung contact in the jack.
If that works, then stick a battery in it and follow DC voltage. Ground the meter to the shell of the input jack, and with the red probe go tight to the + terminal of the battery. Is there +9v from there to ground? The red wire from the battery snap should be +9, and should solder to TP1 on the board. 9v there? Now look at the three terminals on the power jack, is 9v on one of them? Is 9v on the other one? At this point we should see +9 on the two power jack terminals that do not go to the center pin.
And look closely at the solder on the power jack, it could be cracked.
What do you mean by the shell of the input jack? I just used the small lead on the input jack that is connected to the black wire connected to the battery.. will that work? Because i get about 9.2 v from the top of D2 to that.
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