When a Chroma sounds oddly or does not auto-tune reliably, 16 oscillator, filter and VCA circuits along with a handful of CMOS ICs are waiting for a check-up. Although the Chroma’s firmware has functions to support troubleshooting, several devices are hard to diagnose without the possibility to test the voice boards outside of the instrument.
That’s why I built a simple test jig which allows to set all functions and parameters by means of DIP switches and potentiometers.
With this set-up, verification of flawless function takes not much more than half an hour for all eight boards.
The board shown here has several faults – from two intermittent electrolytics over a broken 4556 CMOS 1of4-demux to a dead 4051, the latter two having been identified using the test jig.
Although this jig is rather primitive compared to my later design (Wave 2.2/2.3 test jig), it is still very helpful.