a look inside a roland mks-7

[stecykmi]

hey all, i bought this cool little rack synth a while back, only semi-functioning. i recently got it back on the bench to put the finishing touches on the repair. the mks-7 is largely based on roland juno 106, with a stripped down roland TR-707 tacked on for good measure. the juno 106's (and mks-7's, as the use the same chips) are notorious for failing because of the poor design of the analog VCA/VCF "chips" (they are actually boards with discrete components, not actual silicon chips). that's just what happened to this guy. Luckily, someone managed to perfectly clone the necessary chips, so after buying a couple of the so called 80017A VCA/VCF chips here, i opened her up, removed and replaced the chips and went through the calibration procedure. the service manual for this device is both excellent and readily available so i more or less knew what i was doing before i got started, making this a pretty easy fix considering the complexity! the PCB also features convenient test points (being analog, each unit had to be calibrated by hand). unfortunately, another one of the original 80017A's is malfunctioning, so it'll have to be replaced before too long (i believe this reduces my chord section from 4 to 3 note polyphony). I will likely just spring and replace the remaining original chips as they are likely to fail at some point anyway.

front panel


case opened. the tan board with the large electro caps on the right is the power supply board. the boards at the top are the midi input (if you look close you can see the white optocoupler chip), just beneath it is the mixer/output section. the chorus is also located on that board (based on 1 MN3006 and 2 MN3009's). The large, green PCB is the main board which controls the melody and chord sections, the two white chips were the replacements for the dead ones. the bass section is generated underneath the melody and chord PCB, i believe it's based on a square wave DCO. the drum section is also located on that board, it's entirely digital sample based so nothing really to tweak there.


another shot of the main board


another shot of the output/mixer board