Reparing a Roland TR-909

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Roland TR-909

Recently I was handed a Roland TR-909 and I have spent some time going through its Voice board and PSU board circuits. Repairing what was either missing or broken. Sharing my thoughts here of what I have learned.

Missing BA662 IC

This IC was missing from the board. The BA662 is supposedly what gives Roland equipment it's 'unique' sound.
A thorough write up of the IC can be found here. In the TR-909 it is used in the hand clap circuit. Labelled here as IC30 BA662-A


I was able to find a SMD based reverse engineered clone by Open Music Labs

Broken Noise Circuit

Replacing the PSU

Broken switches