This particular LFO chip might function by writing configuration values to a series of registers and have a low frequency analog waveform come out the other side of the LFO chip. Cheap microcontrollers like the AVR do a good job at making low frequency analog waveforms by using pulse-width modulation. Basically the high +5V state is turned on for a percentage of a period and turned off for the rest of the period. A compressor/resistor combination smooths out the the on/off cycles into an analog level.
Even though it's impossible to get a replacement for this LFO IC, is the data sheet available? Or any information on the chip? Microcomputer techs sometimes make a custom 'mini-logic-analyser' to find out what the main CPU is writing to a peripheral chip into an old logic board. They will put eight input lines of a port onto the data bus going into the peripheral chip, several lines on the address/register bus, and one or two lines on the peripheral chip's read/write line to act as a trigger. When the CPU writes data to the peripheral IC, the data gets captured. Sometimes it works if the peripheral IC isn't too complicated.
Do you know anything about the operation of this LFO chip?
--- On Wed, 7/29/09, John Henson wrote:
From: John Henson
Subject: [vintagesynthrepair] Yamaha IG00150
To: synth-diy@...
Cc: vintagesynthrepair@yahoogroups.com
Date: Wednesday, July 29, 2009, 7:36 AM
Hi list,A client of mine has a CS30 with a dead LFO chip.It seems pretty well unobtainable, but my question is this.Was it a chip rebadged by Yamaha (ie a 566 or a 4151) or has anyone produced a module to emulate it?All the bestJohn