Jan 8, 2011
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Central Coast
I better admit upfront that I play guitar and that keyboards are something of an adventure. I'm getting my home studio to an almost useable (well nearly!) point and have run into a little trouble with an old piece of gear.

I have a Roland U-220 and a Yamaha TX-7 that I intended to use with my Evolution midi keyboard. It seems that it's not a simple midi channel problem as I'd hoped. I can connect the TX7 to the keyboard and all is well. If I connect the U-220 I get nothing. No indication of mid input on the front panel LED. No signal at all. If I connect the keyboard to U-220, thence midi out to TX7 you would think that the TX7 should just work as before? But I get nothing.

Not having a service manual I found a midi spec document that generally describes how these things work. Using a multimeter, I can measure a reverse diode input on the U-220 and DIN connections to the board. On the optoisolator (?) I can measure 4.8 VDC (pins 7 & 8) so I expect that is close enough to 5V. Does this mean the isolator is shot? As best I can understand, if the optoisolator on the midi input works (in spite of the equipment it is connected to is working) than the midi out and thru should work? Does this sound right? Anyway, any help greatfully received. My lousy eyesight really makes working on these things a real challenge.
Tom Watson


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