Roland 80017a

via this auction for the 80017a

"Problems Typically Solved by Replacing the Failed 80017a Chip Include:

* Erratic or sudden loud noise from synthesizer output, particularly after 10 minutes of powering up.
* Note hang-ups or long sustain.
* One synth voice will not respond to filter or amplifier changes.
* Unstable operation.
* Juno-106 or MKS-30: Notes will not play, most typically every 6th note will not play due to failed 80017a chip.
* GR-700: One particular voice or string will not sound, "D" string, "A" string etc.

The sound of the failure will change depending on which part of the circuit is not working: the VCF or VCA for example. The above example is provided to illustrate one type of failure. Your synth may have different symptoms as listed above. About the 80017a VCA/VCF chip:

The 80017a chip was a real workhorse for Roland synthesizer engineers in the early 1980s. This one chip contained both the classic, driving -24 dB voltage controlled low-pass filter with a smooth voltage controlled amplifier. By placing all the components on one chip, Roland was able to keep the classic sound of their analog synthesizers across various products, with low production costs. Almost immediately Roland knew they had a problem on their hands, and changed production methods.

When these chips fail, sometimes voice will stop working completely. On a keyboard synth, this shows up as every sixth voice not working. On a GR-700 guitar synthesizer, this shows up as one string’s synthesizer voice failing. But the chips may not fail completely, resulting in a lack of control over the filter quality for one voice, or by sudden, loud erratic sounds from the synthesizer. The only solution to these problems is to replace the existing 80017a with a new chip.

This chip is from lot 50, produced after Roland solved the manufacturing problems. Probably 20 years after the original production date, this chip is still working well without failure."

You can find scans for the following all via the auction here
Juno-106 Service Manual
Roland Service Note
MKS-30 Schematic
Juno-106 Failed Chip Test Procedure
Juno-106 Calibration
GR-700 Calibration