[sdiy] A part for a CS20M

[Steve Lenham]

A few years ago, an eBay seller was auctioning a CS20M service manual 
and a CS80 (the synth, not the manual). I bid on both - guess which one 
I won? :-(

The fact that I can now tell you what the YM617 does is little 
consolation, frankly (the '80 went for £1800, which seemed like a lot at 
the time!).

Anyhow, the YM617 appears to be part of a subsystem designed to scan 
panel pots and switches, store/recall them to and from RAM and demux 
them to CVs. It's very like Roland's Computronic system used in the 
Jupiter-4. Multiple YM617s are used both to mux and demux the CVs.

In essence, it is a 10-to-1 analogue switch. However, unlike the 4051, 
etc. there are no address inputs. Instead there is a clock input, a sync 
input and a sync output. A pulse on the sync input resets an internal 
counter, which then increments with each clock pulse. The counter 
determines which of the analogue poles are connected to the COM line. 
The sync output allows multiple devices to be cascaded, with the sync 
pulse propagating through the chain.

Just for fun, they run off of +5V and -10V.

You could probably clone them with a 4067 or DG-series analogue switch 
plus a 15V-CMOS decade counter and some gates to handle the sync. Since 
AFAIK they were only used in the CS20M and CS40M, you might have to :-(

In the CS20M, the clock and sync pulses are generated by another Yamaha 
custom device which integrates ADC and DAC for CVs with RAM interfacing 
and the cassette interface.

Why would they do this? Dunno - more integration = lower chipcount = 
better reliability?

HTH,

Steve L.


On 01/07/2013 17:30, MTG wrote:
> OMG, why would they make a custom chip for a relatively standard
> function like this?  What's the COM line hooked up to in the synth? Or
> better yet is there a link to the CS20M schematic? I imagine there would
> be a standard chip workaround, however the amount of work required
> remains to be seen.
>
> GB
>
>
> On 7/1/2013 9:14 AM, John Henson wrote:
>> Hi all,
>> I am looking for a chip for a Yamaha CS20M, it is called a YM617 on
>> the chip, and the Yamaha IC guide calls it a YM61700, it is a serial
>> multiplexer, and the failed one runs the patch selection LED's.
>> Does anyone have any of these, or knows where to get them?
>>
>> Regards,
>> John.
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