If it is receiving midi signals and responding as it should then the opto is fine If you have an oscilloscope check for data pulses at pin 11 of IC22. If ok, check if you get an inverted set of pulses on pin 10 of IC22. If ok check for inverted pulses on each side of R18 R17 should have approx 5 volts on each leg ( just a current limiting resistor for the midi supply) Now if all that is good, you either have a midi socket with poor connectors or dry joints in that chain above. Not much special to midi thru. IC22 is a 74LS06 TTL hex invertor - just buffers and inverts the output of the midi in opto
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Re: sequence the SDS-V
2015-09-24 by Richard Warland