Vintage Synth Repair

Symptoms: Synth would boot up fine and operate ok via the display but no sound, only a nasty snapping and crackling in the outputs. Passed all ROM and other tests. Jack Board verified ok in a working JD800. Main board in question was an obvious victim of a Coke spill.

Removed, cleaned, and replaced the main program ROM, CN10 and a few of the square black filters around CN10. CN10 is the connector carrying serial, timing, MUX, and clock data to the Jack Board for D>A conversion to sound.

After solder ops above, let the board sit in a warm water and Dawn mixture for about an hour, worked it in and around with a soft chip brush occasionally. Rinsed in deionized water and sprayed with canned air. Heated kitchen oven to 170 °F and turned off. Inserted the mostly-dried board into oven and left overnight.

Reinstalled in synth and no longer crackling. Only total, dead, complete, utter silence. DAMMIT!

Checked CN10 pins with a scope. MUX muxing. Serial serialing. Timers timing. Clock signal going into FL7 inductive t-type filter but not coming out. HA! 

The raw, unfiltered signal looked good enough to drive a chip, so I removed the Panasonic filter and simply jumpered where FL7 used to be. Has been working fine now for several hours.

Working to source a replacement filter for long-term stability, but you gotta love it when a plan comes together.