Let's Get Technical > Troubleshooting Problems

MB-1 no output

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peoriashows:
I mentioned this to MarshallJMP over an email, but thought I'd bring it here in case anyone else needed help troubleshooting. One of my MB-1 bass preamps is not outputting sound. Input jack seems okay. When I hook a signal generator up to it, I can see a signal out on the Direct out pins, but nothing on the 1/4" output jacks (full, high, nor low) I'm wondering if the problem is starting back at the HP input on sheet 3 of the schematic. What is the K402? Is that the connector for the volume pot? I tested the pot and get continuity. Any suggestions or where to go from there? Thanks.

peoriashows:
Sheet 3

rnolan:
Do you get anything on the Loop sends ?  Also clean the Loop return jacks, they are serial loops and will break the signal chain before the output (they are switching jacks which can fail due to gunk/corrosion).  IIRC the direct out is just a split off the input jack, so before the gain, eq, etc.  The signal at the Loop sends (and they should always have signal) is after the gain and eq, so if you have signal there, then the issue is later in the signal path.

MarshallJMP:
Do you have a scope?

peoriashows:

--- Quote from: MarshallJMP on July 25, 2018, 07:38:27 AM ---Do you have a scope?

--- End quote ---

Yes, I have a scope I'm getting a good signal on many of the input components. I'll check the Loop sends tonight when I get home.  Thanks. That didn't even occur to me. Would they still effect the output signal if they're not turned on with the patch I'm testing with?

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