H i Guys
I'm hoping someone can point me in the right direction with diagnosing a fault on a guitar pedal. The pedal is working as far as I can tell, but, the output is barely audible. I have measured some voltages on the board which are correct, i.e. the supply voltage to the chips etc, however I have noticed that the negative supply to the op amps are not right. When the pedal is plugged in and powered up both negative and positive supplies to the chip are there, but the negative supply is showing a positive voltage. when I then connect the input jack I don't get any voltage on the negative pin of all the op amps. Can someone please take a look at the schematic and tell if this seems correct. I have checked the datasheet for the op amp and it says it can be run as low as +-2v and up to +-7v, I am reading 8.7v on the power pins off a 9v power supply. I don't know if these readings are anything to do with the issue of the output been barely audible.
So my questions are as follows:
1. Where in the circuit is the negative supply being generated?
2. Does the issue of it being barely audible suggest an input amplification stage or an output stage? and could you point my in the direction of where this is likely to be in the circuit. I'm guessing its an op amp issue, but could be transistor problem.
Also the schematic has labeled the op amps as 1/2M5218AL, but my pedal is using NJM14558L and NJM4558LD. Maybe they updated them at some point.
Any help would be greatly appreciated.
Thanks
I'm hoping someone can point me in the right direction with diagnosing a fault on a guitar pedal. The pedal is working as far as I can tell, but, the output is barely audible. I have measured some voltages on the board which are correct, i.e. the supply voltage to the chips etc, however I have noticed that the negative supply to the op amps are not right. When the pedal is plugged in and powered up both negative and positive supplies to the chip are there, but the negative supply is showing a positive voltage. when I then connect the input jack I don't get any voltage on the negative pin of all the op amps. Can someone please take a look at the schematic and tell if this seems correct. I have checked the datasheet for the op amp and it says it can be run as low as +-2v and up to +-7v, I am reading 8.7v on the power pins off a 9v power supply. I don't know if these readings are anything to do with the issue of the output been barely audible.
So my questions are as follows:
1. Where in the circuit is the negative supply being generated?
2. Does the issue of it being barely audible suggest an input amplification stage or an output stage? and could you point my in the direction of where this is likely to be in the circuit. I'm guessing its an op amp issue, but could be transistor problem.
Also the schematic has labeled the op amps as 1/2M5218AL, but my pedal is using NJM14558L and NJM4558LD. Maybe they updated them at some point.
Any help would be greatly appreciated.
Thanks
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