Working on an old CR1604, some noisy channels in the XLR10 expander. All semi-conductors measured good. Swapped IC's with good channels, no change, swapped transistors, no change. Swapped protection diodes and problem solved.
Just wondering if anyone has any tricks for locating such problems. Couldn't see the noise with the scope until the output of the IC. I tried freeze spray but everything is so close together I couldn't be sure I wasn't freezing everything.
Is this a common fault? What would be a likely cause or was it probably a bad batch of diodes? The bad channels were all close together, 12-16. Was thinking maybe phantom power related but wondering why the diodes would get noisy rather than pop.
Just wondering if anyone has any tricks for locating such problems. Couldn't see the noise with the scope until the output of the IC. I tried freeze spray but everything is so close together I couldn't be sure I wasn't freezing everything.
Is this a common fault? What would be a likely cause or was it probably a bad batch of diodes? The bad channels were all close together, 12-16. Was thinking maybe phantom power related but wondering why the diodes would get noisy rather than pop.
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