EMU Vintage Keys Midi In Fix

Dan Lavin

Just a little post for anyone needing to repair an Emu Vintage Keys 9045 module. I bought it off ebay from the previous owner who complained about intermittent note playing with the unit. Since the demo played just fine, I hooked up various midi keyboards to the unit and confirmed that notes wouldn't always sound when keys were pressed.

I suspected the opto-isolator as it's function is to protect the rest of the circuitry when hooked up to an external unit. I've seen this issue before on my own equipment and other ebay buys. The opto-isolator was either damaged or has just worn down over the years.

I opened the unit to find the opto-isolator was an unknown-to-me device: the NJL5127D. Long searches on the internet did not turn up a proper data sheet. I was only able to find a 1 page short form summary of a couple dozen NJL devices. It only listed a few specs and showed no pin out.

I highly suspected the device was a drop in replacement for the Sharp PC900V because that was “the” device to use in this application at the time the module was made, (1993). I sketched up the schematic per attached and determined it was pin compatible with the PC900V. I unsoldered the NJL5127D and soldered in a socket, just in case my assumptions were all wrong, and placed the PC900V in the socket. The unit now works like a champ. No more missing notes despite all the midi data I could throw at it.

Interesting to note was the use of a transistor instead of a diode for input protection. Since an NPN transistor can just use a single PN segment, it effectively is a diode. I should note these components are all SMD with the exception of the opto-isolator. Maybe the transistor package is easier to handle than a SMD diode? That would be my guess.

EmuVintKeysMidiInCircuit.pdf

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schematic

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blue hell · Posted: Sat Feb 28, 2015 1:16 pm Post subject:

Nice fix :)

BTW - SMD diodes come with two in a three pin package at times. Especially the Schottky types it seems, maybe because these are often used to clip a signal to ground and supply voltage ... don't know really, just saw it often.

Dan Lavin · Posted: Sun Mar 01, 2015 11:21 am Post subject:

Jan' Thanks! Of course that makes sense about the diode/transistor confusion on my part. Based on your post and the fact that the pcb legend calls it out as a "CR" instead of a "Q", I'm guessing it is a 3 legged diode. Just showing my lack of SMD experience!