Strange problem with BOSS FBM1 Pedal?.

saltyseadog

New Member!
Jan 14, 2023
5
UK
I use a Boss FBM1 effects pedal as I like the distortion. The pedal works fine, the knobs all turn and do what they are supposed to do. I use the proper Boss 9v power supply on it. With this pedal connected when I use the volume controls on either my Strat or ES335 I get that scratchy dirty pot sound but only when rotating the knobs. Now I can hear you thinking it's dirty volume pots on the guitars but no, as if take the FBM1 out and plug either guitar straight into the amp the knobs are perfectly quiet with no scratchy sound at all. I also have a delay, a tremelo, a chorus and a Vox Wah pedal on my board and there is no scratchy sound problem when I use them. The problem certainly seems to be in the FBM1. Does anybody here have any idea what would cause this and if so. how do I fix it?.
 

keys88

Strat-Talker
Apr 4, 2014
336
Columbus, OH
People smarter than me will be more helpful. But just out of curiosity, does it make the crackling sound with the pedal off? Or is it only when the pedal is on? Have you taken a look inside the pedal to see if the jacks are loose or if anything looks out of place? Also, sometimes pedal noise can be a result of a bad power source. Have you tried using a regular 9v battery just to see if there's something wrong with your power supply?
 

saltyseadog

New Member!
Jan 14, 2023
5
UK
Thanks for the reply, the crackling sound happens with it both on and off and the power supply is okay. After reading your post though I opened the pedal today and can see that either a resistor or capacitor named L1 on the board is blown. I have tried to search and download a schematic for the FBM1 without success, I did find a post saying that you can't get a schematic for it due to it being COSM technology. Thought I would try and contact Boss UK but the pedal is out of production and all I can get is the owners manual which I already have. Anyone have any idea of what the L1 would be?.
 

keys88

Strat-Talker
Apr 4, 2014
336
Columbus, OH
Shoot, I forgot those are COSM pedals. I've done some modding and I've built a couple StewMac pedal kits, but if I had a digital modeling pedal that wasn't working right I would probably just send it to the manufacturer for repair. It's not like modding/repairing an analog pedal. Do you have any pics of the blown part? Does it look like a standard resistor or capacitor, or is it some micro electronic part?
 


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