Some of my friends and customers used to joke around about my magic screw driver as problems seem to disappear when I show up. (Did you bring your magic screw driver?!) My cousin Mike Spikes of American Toy, llc was inspired to draw this sketch.

I became a professional electronic technician when micro processors had 8 bits and ran on a 3.14 mhz clock - 1973. I excelled at component level trouble shooting working on early graphic workstation terminals for Tektronix. In 1977 I quit Tek and started Musician's Bench in Portland, OR. Portland needed someone to provide this service at the time so it was easy to sign up for accounts with Arp, Moog, Oberheim, SCI, Roland, Yamaha, Fender Rhodes, Wurlitzer etc. I attended factory training at most of these companies and provided service in and out of warranty during the "glory years" of American designed and manufactured electronic music gear.

Disgusted by dealings with the public at large and other non technical aspects of running the business, I was inspired to get away from the store front repair operation. A following of loyal customers from the past still keeps me in the business at a hobby level and I've kept all the documentation, parts and other resources required to work on a lot of vintage gear - mostly keyboards.

My favorite customer is the owner who wants to learn what they can about working on their own gear. My passion for sharing knowledge and the willingness to do so keeps me connected to the repair business.

Read and learn from these music tek bench stories!

Music electronic technician Larry Church discusses various bench projects with relevance to teaching basic skills valuable in working on vintage music equipment. Larry attended factory training at companies such as Arp, Moog, Yamaha and Sequential Circuits, and provided warranty service for these companies and others such as Rhodes, Gibson, Wurlitzer, Marshall, etc.. Basic skills, common sense, general knowledge and trouble shooting mentality are discussed here.

Monday, February 8, 2010

Oberheim custom wiring harness

My customer, Michael, invented this configuration of an SEM, MS-1A mini sequencer and a mixer module.  He intends to integrate this into a larger patch that will include at least one other mono synth slaved to the sequencer and one or two external gate and CV controllers.  Oddly, the MS-1A Michael procured for this project has had the front panel paint stripped off.

A good wiring harness design includes these three important  aspects. 1:  Interconnects system components as per the electronic schematic such that the function of hardware is not compromised by the interconnect system.  Attention to proper grounding, shielding and cable routing is important.  2:  Implements serviceability by providing access to, and easy disconnect from, all components in the system.  3. Does not degrade reliability - wires are bundled and secured such that stress is equally distributed over all wires and connections.  Good quality stranded hookup wire and proper crimping and solder techniques are crucial in achieving professional results.  Sloppy work, lack of planning and inferior materials can significantly erode the success of a wiring project like this.

Michael found a web site that lists all the connector pins and their function on the SEM and MS-1A along with their recomendations for building a patchable system.  With this information Michael produced a panel layout fitted with 1/8" 2 conductor jax.  My first input was that a bunch of those jacks need to normalize a predetermined signal connection.  For example, one of the VCO CV inputs is generally connected to a 1 volt per octave Key CV.  Replacing the standard 2 conductor jack (Switchcraft 41) with a normalizing jack (Switchcraft 42A) allows for a pre-wired patch connection on that signal line. 


  1. great work larry! not only does the unit sound awesome, its functionality is even better than i originally thought it would be

    many thanks!

  2. Larry - where are you located? I like your blog here and I want to learn all I can.

    I got a bum Ensoniq SDP-1 that isn't making sounds (you can hear a faint sound. Hope you are in So Cal? Cause I am. Would bring it to you to see what you think.

    Mike Learmouth

  3. Hey, it's Kevin Lightner.
    Good work on that synth.
    I saw that MS1A before.
    Strange with the panel stripped.
    I have artwork for it, but it isn't hard to operate without.
    Take care!


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