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How do you tell if an inductor is bad in a wah?


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I have a Crybaby that is around ten years old. It just quit working one day and I just never used it again. I was bored yesterday and pulled it apart and painted the case. While I had the board out I found that the 9v adapter plug had two broken solder joints. I fixed those and its still not working. When the switched is clicked on the sound is just gone. Could it be the switch or the inductor? I am planning on buying all of the parts to mod it and make it work again. Is there a way to test it with a multimeter?

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The inductor is just a coil of wire wound around a piece of ceramic. It's very unlikely that's where the problem is. I would check the moving parts first: the switch and the pot.

 

Yes, you can do a simple go/no go test with a mulitmeter, but it's probably best to remove the inductor from the board, because there's a resistor in parallel with it that will throw off the reading. But don't bother because either your switch is bad or you didn't make a good repair on the power jack.

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The inductor is just a coil of wire wound around a piece of ceramic. It's very unlikely that's where the problem is. I would check the moving parts first: the switch and the pot.


Yes, you can do a simple go/no go test with a mulitmeter, but it's probably best to remove the inductor from the board, because there's a resistor in parallel with it that will throw off the reading. But don't bother because either your switch is bad or you didn't make a good repair on the power jack.

 

Cool, thats what I needed. I am 95% sure its the switch. When I click it on the sound goes away almost completely and I can wiggle the switch around and hear it crackling. I want to mod the circuit board anyway so I am going to put a new DPDT switch in it and make it true bypass:thu: Would it be worth it to get a new inductor or should I just leave it stock?

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Would it be worth it to get a new inductor or should I just leave it stock?

 

I replace the stock TDK inductor in my early 80's crybaby with a red Fasel inductor. Not much difference to my ears, if anything the fasel sounded a little thinner. But at least a new inductor is fairly cheap ($18 mail order) and it's about the simplest mod you can do to a pedal. Your mileage may vary.

 

Read up about modding your crybaby for true bypass, the later models with the jacks soldered to the PC board require you to break a trace on the back of the board to make it true bypass.

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I replace the stock TDK inductor in my early 80's crybaby with a red Fasel inductor. Not much difference to my ears, if anything the fasel sounded a little thinner. But at least a new inductor is fairly cheap ($18 mail order) and it's about the simplest mod you can do to a pedal. Your mileage may vary.


Read up about modding your crybaby for true bypass, the later models with the jacks soldered to the PC board require you to break a trace on the back of the board to make it true bypass.

 

I read that as well. I'm not out much if I really screw something up LOL. Its been sitting around for years collecting dust. I figured If I wanted to try my hand at pedal modding that it would be a good place to start:cop: The case turned out pretty nice looking. I will get some pics up soon.

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I still cant figure out the problem with this thing:facepalm: I tested the switch and pto with a multimeter and they are working fine. When I tested the inductor I got a reading of 17.5 ohms and thats what it reads across the 33k resistor as well. Is that reading correct or do I have a problem?

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As said, you can't test the inductor in circuit or with a dc vom.

 

You need to inject a signal (AC) and trace it to loss.

 

I don't think an inductor coil is going to go bad unless it was underwater, plugged into a house outlet or hit with a hammer.

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When a wah inductor goes, it usually goes open as the result of dropping the wah. The inductor has a low DC resistance--normally under 75 ohms. The 33k resistor is in parallel with the inductor, so the in-circuit resistance measured across it should be lower than the inductor's resistance. If you measure a high resistance here (around 100 ohms) then the inductor is probably open. Since you're reading 17.5 ohms, your inductor is not open.

 

If I were you, I'd recheck your DC jack repair and then look for cold solder joints and broken solder joints or traces. Use your multimeter and check all connections to ground or power. Also, measure the transistor voltages and post them here.

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If we do the math, we can see that a 33K resistor needs to be in parallel with a 17.5 ohm resistance to yield a resistance of 17.5 ohms (actually about 12.495 ohms).

 

If you were out of circuit and assumed a 500mH inductor had a dc resistance of 75 ohms for instance, the reading would be around 74.83 ohms.

 

You can't do that test in circuit is my point.

 

Checking transistor voltages is a good idea if you can't do a signal trace. But it won't really reveal which component is bad. Just that something is bad.

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I don't think an inductor coil is going to go bad unless it was underwater, plugged into a house outlet or hit with a hammer.

 

I understand your point, and yes, an inductor cannot truly be tested in circuit, but one can check if the inductor has gone open which I've seen happen countless times due to wahs being dropped. That was my point in response to the OP and not in response to you. I've measured resistance on Dunlop inductors all over the board from the high teens to the mid seventies on the ohms scale, and so I said "normally under 75 ohms" and not "precisely 75 ohms." I'm sorry for trying to be helpful to the OP using the information provided. It is reasonable to assume from his line of questioning that he probably is unable to do a signal trace.

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I understand your point, and yes, an inductor cannot truly be tested in circuit, but one can check if the inductor has gone open which I've seen happen countless times due to wahs being dropped. That was my point in response to the OP and not in response to you. I've measured resistance on Dunlop inductors all over the board from the high teens to the mid seventies on the ohms scale, and so I said "normally under 75 ohms" and not "precisely 75 ohms." I'm sorry for trying to be helpful to the OP using the information provided. It is reasonable to assume from his line of questioning that he probably is unable to do a signal trace.

 

I'm not trying to argue with you or discount your troubleshooting. My replies are based on your point, if he can't do this or that, the other is probably out of reach too. I doubt the transistor voltage values, even if given to us, are going to help him either though.

 

Just by reading your reply I can tell you are experienced and mean well. Again, I'm not arguing. I'm trying to reinforce that this is likely not something that he is going to learn to do, let alone pull off, from a conversation on the net, especially as you point out, he doesn't likely have the right tools.

 

We don't even have a model and schematic here. For all we know it's buffered and the buffer is bad, not the wah circuit.

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I'm not trying to argue with you or discount your troubleshooting. My replies are based on your point, if he can't do this or that, the other is probably out of reach too. I doubt the transistor voltage values, even if given to us, are going to help him either though.


Just by reading your reply I can tell you are experienced and mean well. Again, I'm not arguing. I'm trying to reinforce that this is likely not something that he is going to learn to do, let alone pull off, from a conversation on the net, especially as you point out, he doesn't likely have the right tools.


We don't even have a model and schematic here. For all we know it's buffered and the buffer is bad, not the wah circuit.

 

I apologize for misreading the tone of your words and reacting defensively.

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I apologize for misreading the tone of your words and reacting defensively.

 

That's the problem with writing rather then conversation. I'm sure if we were at a bench together we'd have fixed a bunch of stuff by now.

 

I truely want to help and if I had asked, I'd take your advice for sure. I didn't mean to be nit picky either.

 

I probably did come on too strong. My confidence level is rather high having fixed an 80's crybaby and a 1967 Vox Clyde McCoy Signature wah in the last couple of months. But I still have room to learn.

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Thanks guys! You guys are right, I dont know a ton about stuff, just enough to be dangerous:cop: LOL. Anyway, its a standard Crybaby that I am working with. I dont think I mentioned that. I removed the buffer circuit from the board as I am going to put in a 3PDT switch to make it true bypass and add an LED. I did continuity test for alot of the components and tested the value on the pot. when everything is plugged in I get signal just fine with the wah off. As soon as I turn it on the signal is either completely gone or very faint. I looked over the board pretty closely and didnt find any broken traces or solder joints. What else could I test on this thing?:lol:

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Well, the bypass is working, that's one good thing.

 

When you ripped out the buffer, did you use a specific schematic and procedure? Maybe you just missed a trace cut or needed jumper? Can you link to the procedure you chose to follow for the project?

 

Don't rush, you can get there. Just regroup. Using some test points as imbuedblue suggests, perhaps we can do some comparison tests on another known working circuit to see where you are. We just need to get equal circuits and we'll need a schematic to be sure we get that.

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Just to clarify, you have removed the input buffer but haven't replaced the switch with a DPDT to wire it for true bypass yet. Correct? If so, you have disconnected the input jack from the effect input. In the stock switching arrangement, the input jack is always connected to the effect input. If you look at the diagram you linked to, there is an extra green wire added from an empty pad to the new switch. This wire goes to the effect input and the DPDT switch connects it to either the input jack or ground.

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Just to clarify, you have removed the input buffer but haven't replaced the switch with a DPDT to wire it for true bypass yet. Correct? If so, you have disconnected the input jack from the effect input. In the stock switching arrangement, the input jack is always connected to the effect input. If you look at the diagram you linked to, there is an extra green wire added from an empty pad to the new switch. This wire goes to the effect input and the DPDT switch connects it to either the input jack or ground.

 

Thats correct. I removed the buffer but I havent added the switch yet. My components will be here today so I will get to work on it this weekend and see if I can figure it out. I only tested it in the stock configuration. I really think its the switch. I will find out for sure when I put the new one in. I will let you guys know! Here is a pic of the case that I painted...

wahpic.jpg

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Thats correct. I removed the buffer but I havent added the switch yet. My components will be here today so I will get to work on it this weekend and see if I can figure it out. I only tested it in the stock configuration. I really think its the switch. I will find out for sure when I put the new one in. I will let you guys know! Here is a pic of the case that I painted...

wahpic.jpg

 

Well, if you removed the buffer at the same time that you resoldered the DC jack, then you may have fixed the problem while creating a situation where you couldn't test the outcome. Like I said before, by removing the buffer you have disconnected the input jack from the effect input which means the wah will not work with the stock switching unless you add a jumper from the jack to the effect input.

 

Anyway, nice paint job!

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Well, if you removed the buffer at the same time that you resoldered the DC jack, then you may have fixed the problem while creating a situation where you couldn't test the outcome. Like I said before, by removing the buffer you have disconnected the input jack from the effect input which means the wah will not work with the stock switching unless you add a jumper from the jack to the effect input.


Anyway, nice paint job!

 

I actually tested it AFTER I resoldered the power jack with the buffer in its stock form. I didnt take the buffer out until I found that it still wasnt working. Does that make sense? I basically tested everything I could before removing anything from the board.

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