Yamaha QX3

I recently won an eBay auction for a "spares or repair" QX3 sequencer. It looked bad from the photos, but was very cheap. It turned out to be worse than expected. The case was held together with gaffer tape as and the PCBs were loose inside as almost all of the plastic screw posts had crumbled to nothing. It was also absolutely filthy, but a quick test showed it at least booted.

These used to be screw posts

The keyboard. Filthy and missing a few keycaps

Cherry key switches - and 30 years of crud!

I stripped the case of all electronics and gave it and the keycaps a bath and cleaned up the key frame and PCBs. Copious amounts of epoxy were used to attach new plastic standoffs to replace the broken screw posts. I managed to break one off on reassembally, but the rest seem solidly attached.

New screw posts glued in place

The floppy drive was full of dust, so this was cleaned up and reassembled, before being reinstalled.

Electronics cleaned up and reinstalled

Further testing has found that the sequencer basically works, including the floppy drive, but the encoder is jumpy and only works in one direction and a few of the keys are intermittent. I have removed, opened and cleaned the encoder and the worst of the key switches, but will probably end up doing every switch.

Still to do:

• Reinstall the encoder and check that it now works.
• Check the rest of the key switches and clean as required - or just do them all.
• Replace tact switches - these are the same as the ones in the Juno 106 and I still have about 70.
• Replace the mains flex.
• Replace missing key caps - I'm unlikely to find the correct ones.

Roland MKS-30 modification

I intend on getting a Kiwitechnics patch editor at some point, but the latest revision of it no longer supports emulation of the Roland PG-200 programmer, so cannot control a stock MKS-30. I believe the MKS-30 was the first MIDI module produced and it's MIDI implementation is severely limited - basically note on/off, no sysex or CC. The only way to backup patches is with an expensive and rare memory cartridge. Editing via the front panel is a painful process and the original PG-200 programmers go for as much as the synth itself, but thankfully Johannes Hausensteiner came up with a rewritten firmware and minor hardware modification that allows saving and loading patches over MIDI as well as realtime control. There is also a mod to control the speed of the chorus at the expense of being able to adjust the high pass filter, but I decided to forgo this.

Lid removed to expose the guts of the MKS-30. The mod comprises a replacement EPROM and a single wire from pin 12 of IC 40 on the main board to R12 on the chorus/PSU board.

Closeup of the main board changes. Rather than solder directly to the IC pin, I used a Molex connector so that the boards can be separated easily when I inevitably have to replace the VCF/VCA ICs. There are two conveniently positioned vias here with the right pitch for a 2.54mm header.

The other end of the wire. R12 is disconnected from the MIDI in circuitry and the free end connected to the wire, gunked down with silicon to stop it wandering. This turns the MIDI thru port into a MIDI out.

The infamous Roland 80017A filter/amp hybrids. Two of them have failed in my Juno 106 and it is only a matter of time before these fail too.

Replacement battery installed last week.

In other news, the intermittent front panel button (MIDI channel) is now behaving itself after some massaging. I haven't taken the panel board out to have a look, but I now believe these to be the same as the tact switches in the Jupiter 6, i.e. totally unobtainable.

MIDIpal

This wasn't supposed to be my next project, but I am still waiting on parts for the audio effects units.

I have intended to get a MIDIpal for a while now, but was put off by the surface-mount soldering involved. I finally bit the bullet and ordered one and built it over the last few evenings.

The MIDIpal is a tiny MIDI processor, which can serve as an arpeggiator, a simple step sequencer and delay, among other functions. It is Open Source hardware and available as a kit from Mutable Instruments.

This was my first experience of surface-mount soldering and it actually turned out easier than expected, though I applied too much solder to the ATMega328p MCU, resulting in a short between VCC and ground. Solder wick fixed the short, but left rather a lot of burnt flux behind. As for the resistors, LEDs, diodes and capacitors - soldering was actually quicker than with through-hole parts.

The completed MIDIpal in it's transparent case. Despite the mess around the MCU, it works!

Uploading the firmware using a USBtiny ISP.

I'll post a video once I have had a chance to play with it.