OBERHEIM SYNTH

I thought I would post my issues with my Matrix 1000 not accepting any midi input in case anyone else has any B.S. 

I powered up this module in a new rack to set the gain levels and make sure everything was connected properly. No matter what I used for a controller it would not respond to any midi input. I found the schematics and discovered the opto isolator (IC821) for the midi input was dead. I could see the midi signal on the input but nothing on the output. I looked through all my dead synth gear and could not find an exact replacement for the supposed failed Sharp PC900 opto isolator. Finally after about three hours of searching I found a H11L1 spare that I used for a midi bass pedal project. This opto isolator has a Schmitt trigger for an output so it's a bit unusual for a 6 pin dip iso... I desoldered the original and installed a socket then plugged in the H11L1 and it worked like a champ. Maybe even better than the original which may have been iffy from the beginning.

Let me know if anyone has any issues with their Matrix midi inputs. I learned a bit about all the associated circuitry.

One of your techy moderators,  Fran