Reparing a 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