I have acquired an MB1 that has a very loud hum associated with the Mic 1 input. Changing the Mic gain changes the level of the mic audio but the hum level stays the same. I have been told that the previous owner attempted to use a tube-based microphone preamp to "boost the input" and this caused the hum to appear.
In tracing the cable from the front panel Mic connectors I found the attached resistor, R39_MCU, is burned through. I do not assume this is the full extent of the damage but the resistor is burned to the point were I can neither measure its value nor read it under the microscope. I have the tools and skills to replace this resistor but I need the value.
Can anyone help with this? Even a close up picture of an undamaged board would help a lot.
Warren Allgyer - WA8TOD
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