Korg 770 Synthesizer Troubleshooting Intermittent Pitch Problems

This is a concise, technical, and hopefully well-presented account of how to resolve an intermittent problem on a vintage synthesizer. I learned a lot, and hopefully others could as well. As with all electronics projects take the necessary precautions to prevent electrocution, injury and death.

This old Korg 770 synthesizer was having intermittent pitch problems.
Intermittent problems are the mother-of-all problems to resolve.
Like finding a needle in a haystack...
if your needle is made of glass...
and the haystack takes half a city block.

The keys to the game are four D's:
- Dumping vast amounts of time into the project
- Drawing a map (schematics, diagrams), and marking the places you have already explored.
- Discipline and persistence.
- Deploying the right tools: Voltmeter, Oscilloscope, Iron, and a good rework gun like the Hakko 808.

Other things not covered in this video I dealt with during this restoration were:
- Replaced 3 broken keys
- Re-aligned a bent keybed frame
- Replaced a broken pot and broken switch
- replaced DOZENS tiny pot metal screws that were stripping out.
- Installed a 3-prong AC Power Entry module
- Added an Earth Ground to the chassis

I would like to send special thanks to cykong.com for taking to time to provide graphically enhanced schematics available. Without this I may have not been able to resolve this extremely difficult situation.