Problems with old Midi Matrix switcher (LDR's?)

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Daroka

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Hi,
I have an old Mesa Midi-Matrix switcher (not to be confused with the new product with the same name).
For those of you familiar with the switcher it has 6 loops for effects and 4 amp loops that can be turned on or off.
The in/out jacks for the amp loops are labeled S7, S8, S9 & S10. Recently I noticed that S8 has stopped working. I have
four preamps connected and no matter which amp I connect to S8 I can barely hear the signal. I have opened up
the switcher and cleaned the jacks and electronics, but still barely any sound. Since I can hear a faint sound, I assume the
audio path isn't broken.

I noticed that each amp loop has an LDR/optocoupler and know that these components have caused problems
in other Mesa products. For example failing LDR's are often the reason for a significant volume drop between various
modes on the TriAxis. Thus I assume that this might also be the case with my switcher.

Has anyone had a similar problems with the Midi Matrix or have any suggestions on what might cause the problem?
I have tried to find more information online about the exact function of LDR's and their use in Mesa products. I assume
they have something to do with the volume/signal strength? I haven't had the chance to measure the component, but will
try to do it this weekend.

Any thoughts, comments or suggestions are appreciated.
Thanks!
 
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