Yamaha PSS-140

[untune]

Howdo all, I'm new so please... be gentle

I picked up my first bendable keyboard on ebay a few weeks ago, without really checking first whether it was actually bendable or not... well thank my lucky stars the 140 turns out to be one

I'm aware of the FM chip/data stream mod which I intend to do first, but I'm a little uncertain where to begin... I've located the chips and whatnot involved, using the one reference pic on this page http://circuit-bent.net/pss-270-tutorial.html but apart from highlighting the solder joints the pic doesn't tell me much else... is it necessary to cut the traces between the FM chip and the bigger one? Or do I just solder wires and switches between the points marked red and blue?  What are the ones marked yellow for?

I also noticed one of these going on ebay with pots for drive and distortion... are these bends or more likely additions to the circuit?

Hope i'm not asking too much but I've searched and some stuff still isn't clear to me... thanks in advance for any help

[andy_wheels]

hello there untune,

welcome to the dark side...

yes you have to cut the datalines between the two chips. you are moving the flow of data from the circuit board to the wires you solder to the chips. the switches can then be used to stop the dataflow.

i used a stanley knife blade to cut the datalines. it's very easy to do. just be careful not to cut anywhere else. a small craft knife would be best.

you can find distortions and a few other effects by probing around on the circuit board. use a pot between the probes to 'dampen' the effects of the shorts. a straight connection to most distortion short circuits normally leads to total screams or sound drop outs so you won't know what you've found unless you add some resistance in between the probes...

[untune]

Hi Andy

Thanks for the reply!

I took a pic of the board which is below.  So I'm clear on the red and blue, I wire switches to the matching numbers of the relevant solder points.



I've put a black line where I was thinking of cutting the traces - does this look ok, or is it wiser to spread them out a little and cut each trace at a different point with some space?  I suppose this would be better if I was going to put solder at each side of the cut rather than solder directly onto the pins themselves...

Also I'm still unsure about the yellows... do I cut between these and put switches between them?

Thanks again

[andy_wheels]

yeah, that looks fine but i'd probably do it a little further round to the right where it's clearer.

there are two of the datalines (marked yellow just right of the black line) which use wire jumpers to, erm, jump accross the circuit board on the componant side. if you cut the wire and solder those two you don't need to cut them on the circuit side. makes life a little easier...

hope that makes sense.

[untune]

Hehe, yeah I see what you mean about the jumpers now

So just a case of snipping those little jumpers and soldering the wires and switches on that side.... much better!!!

Thanks for explaining this Andy, you've been a great help

Cheers!

[computer at sea]

You can also do a slight voltage drop crash with this one, but it has be pretty shallow.  After about 35 ohms of resistance the sound dies entirely.  I ended up taking a 1k pot and bridging two pins with a 33 ohm resistor, which makes a maximum somewhere in the low 30's.

It ends up killing the sustain for most voices so you get a very brief tone with a little bit of distortion as well, and on the rhythm presets it removes about every sixth or seventh drum hit.  It drops the overall volume as well, so I put a volume pot in the + speaker line and start with everything at about 3/4 volume.

[nochtanseenspecht]

and don't forget to do "something" with the other pins of the two chips to !
there's so much more inside beside the data lines cut 

[computer at sea]

As nochtanseenspecht mentioned in the PSS thread, connecting pin 16 on the big chip to 11 on the small chip accesses some super low octaves played on the middle to high part of the keyboard.  Also, if you connect pin 16 on the big chip to 10 on the small chip you get the opposite effect and can play very high octaves as well that are triggered by the lower keys on the board.
Here's a few more points.  The letter A after a number stands for the large chip, and B stands for the small

33A, 3B and 33A, 4B.  These both work well with the auto accompany feature playing, particularly if you play some individual notes.  33A, 4B also makes a constant tonal stuttering sound when connected.

1A, 28A.  Functional but not too strange.  When these two pins are connected, whatever notes are currently being played will hold indefinitely. Nice if you need a drone of a specific pitch, and it doesn't cause a crash.  This bend occurs multiple places on the chip.

I'd be curious to hear what other people found.

What have other people found?