UPDATE 2024: I did this almost 20 years ago and no longer have access to a CS-30. A couple of people have mentioned inconsistent triggering with this mod, and that tapping the clock signal at the collector of TR14 instead of the base yields better results.

Yamaha CS-30 clock input modification

this modification adds a switch to the cs30 that lets you clock the sequencer with the external input signal.
you can still use the internal clock to trigger the envelopes at the same time, for complex modulations.
to trigger the envelopes from the external clock (in time with the sequencer), switch them to ext.

i will take no responsibility for any damage to your synth if you attempt this mod.
i actually shorted the power supply and broke a bunch of stuff on my first attempt. make sure the synth is off/unplugged
while you perform this mod.

supplies:
-3 longish stranded wires, with the ends stripped and tinned.
-1 SPDT switch

1. remove end panels
2. remove 2 bolts on underside of keyboard near the ends
3. lift panel toward back (nice hinges!)
4. lift keyboard toward back
5. on left underside of keyboard assemblage, underneath LFO and External Input controls,
there is a circuit board. find (3 solder pads of the) transistor labeled "Tr14"
6. solder a wire from the pad of Tr14 that does NOT connect to Tr15 OR to the 10k resistor (see below)
to one end lug of the SPDT switch. this is the external clock

7. lower the keyboard assemblage
8. on the underside of the control panel, locate the rightmost circuit board
9. locate IC3
10. locate the indentation mark at one end of IC3.
11. starting from the first pin to the right (or clockwise) of the indentation mark, count to the 4th pin.
12. solder a wire from this pin to the other end lug of the SPDT switch. this is the internal clock.
13. follow the trace from pin 4 of IC3 to pin 14 of IC4. it also connects to a 100k resistor just above IC3.
14. 2 options:

A. cut the trace somewhere after the 100k resistor, before pin 14 of IC4. solder a wire from pin 14 of IC14 to the
middle lug of the SPDT switch. this is the clock input.
OR
B. desolder the 100k resistor, poke it through the holes so it falls down where you can reach it, and resolder it
between the junction of Tr26 and the 10k resistor, and the hole that connects to pin 4 of IC3. this leaves the hole that
connects to pin 14 of IC4 open. solder a wire from this hole to the middle lug of the SPDT switch.

basically, whichever option you choose, you are trying to leave the internal clock connected to the 100k resistor,
but disconnected from pin 14 of IC4.


15. install the switch somewhere in the case of the cs30. i actually opted to use the high/low output switch, but to do this you
have to use a continuity tester to figure out how to hardwire the high output.

DONE!

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