Quick note about a quick repair.

The SQ‑64 is a simple-looking but rather complicated digital sequencer which can receive and send CV/Gate/Trigger, Korg Sync, and MIDI signals, which is intrinsically a 64-step sequencer and which can chain sequences etc. It’s handy for translating analogue timing signals and setting up sequences for MIDI devices which can’t take a simple external clock, and so on. It has some limitations as a controller of analogue synthesisers however, but that’s not the topic today.

This SQ‑64 was I think bought new about two years ago, not long after they came out, and has developed a fault, so I’m going to investigate. The fault is that the eighth top row sequence button is activating intermittently without being pressed, which adds unintended gates to a sequence and prevents the user accessing additional functions in some modes because this button is interpreted as being pressed and having priority over other things, somehow.

Opening seems best achieved by removing the four small torx screws at each front and back corner, which allows the top panel to loosen. The encoder knobs have to be removed. At this point it seems to be possible to judiciously lever the panel back over the various socket rims along the back and over the encoder shafts if they’re turned so the flat face is to the front. But it’s better to loosen the four screws in indents on the underside, which hold the circuit board the encoders are on down.

Under the top panel the sequence switch caps turn out unsurprisingly to be a single sheet with some projections for microswitches but the 64 sequence buttons each have a set of four conductive pads on the underside, which bridge some of these interlaced comb contacts on the PCB underneath.

There is a blob of green on one corner of contact 8 (SW42), and something adhering to the conductive pad. This seems to be a fairly normal corrosion fault, but there are no signs of any liquid penetration at the sides of the sheet, just a blob of something green where that one contact sits. So it’s probably a manufacturing defect. What the substance is I’m not sure. I scraped it a bit; it came off the pad under the button easily, but took a little more work on the PCB, eventually, with the aid of a little acetone and a cotton bud (but carefully because the framework around it looks like it might dissolve in acetone), revealing that the final two teeth of the interleaved combs are gone, and the next two are partly corroded. That’s in spite of being gold plated, so whatever the substance was — possibly the glue that sticks the conductive pad to the button? — is fairly severe.

With it cleaned off, reassembly is straightforward. And the fix is successful in functional terms, even if it’s not a proper repair. But this pad probably never worked. This way, the glue (?) isn’t acting as a conductor, and the other three pads for this contact can get on with the job. Not quite satisfying though.

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