Background

This is becoming a popular mod. I first read about it on Table Hooters , and then Kevin Rees published his excellent version of it and I've seen it on other sites, too. Basically, you're loading the registers of the FM chip with some version of garbage, and the resulting sound has random and bizarre elements.

Mine's a bit different. I liked the Tablehooters version that uses just a DIP switch for altering the data lines between the CPU and the FM chip for it's minimalism, but I hate the tiny tactility of DIP switches. Kevin's is nice but that's a lotta external hardware (does this make me less of a bender?).

Anyway, I thought it might be nice to have a changeable but static scrambling mechanism for the data lines, keeping the mod clean and out of the way, and have the ability to change between sounds very rapidly by just pressing and holding one key.

The Modification

This mod's a bit involved. It requires two quad SPDT analog switches in sockets on a perfboard, quite a bit of soldering, and some dexterity with the iron, since mine ended up in a tight spot on the keyboard. Mine also used some "precision" drilling, gluing, etc.

The circuit you’ll be implementing is this:

Parts List

one 16-pin wire-wrap sockets

two 20-pin wire-wrap sockets

Lots of short (2-3”) and longer (6-9”) strands of 30Ga Teflon-coated wire-wrap wire with stripped ends

6+ feet of 8-conductor ribbon cable (rainbow is best for good color-coding)

two small scraps of perfboard: one to fit the 16-pin socket, the other to fit the two 20-pin sockets

SPST momentary switch

~100kOhm resistor

two MAX333 quad SPDT analog switches

Um, don't ask why I used the MAX333's when I could have used the cheaper and more common CD4066. I think I was looking for really low ON resistance, but after I built it I revisited the specs and found that at the 9V supply, the two are not too different. Duh.

Electrical & Mechanical Installation

I don't remember all of it now, but basically:

Get a 16-pin wire wrap socket and size it for placement in the upper outside corner of the keyboard (yes, it's going to be mounted on the OUTSIDE!)

Mark and drill 16 holes, one for each of the wire-wrap terminals of the WW socket.

While you're here, size and drill for the SPST momentary switch.

Wire the teflon wires to the switch before inserting the 16-pin WW socket - you'll have easier soldering access that way.

Insert the WW socket through the drilled holes and glue it in place (for extra mechanical strength, I used a piece of perfboard on the other side and bolted that down, too.)

Prepare a ~6 inch section and an ~18 inch section of ribbon cable, by separating the wires about 1 inch from each end. Strip and tin all the conductors.

After the glue is done drying, wire up the board with the prepared ribbon cable. Note: where I put it, this is VERY tight work with the soldering iron!!!

Now wire up the board with the MAX333's on it, using a combination of wire-wrap and solder.

Size it to be mounted "upside-down" in the top chassis. Mark the appropriate holes for the standoffs on the board and drill through the chassis

Before mounting the MAX333 board, wire it up to the prepared ribbon cable from the 16-pin socket.

Again, before mounting it, wire the MAX333's to the 18-inch prepared ribbon cable

Over on the main PCB, cut the traces that go from the uP to the YM2413 FM chip.

Now solder the other end of the 18-inch ribbon cable to the underside pins or traces of the FM chip on the PCB on the other side of the keyboard.

Now take a 16-pin, 8-component DIP carrier and connect the pins on one side to pins on the other side in any routing you choose. I chose just a single pin offset (i.e., 1 to 10, 2 to 11, ...).

That should be it for the installation.


				*Cheap Mods* *Yamaha PSS-170 FM Scramble*



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		Background This is becoming a popular mod. I first read about it on Table Hooters , and then Kevin Rees published his excellent version of it and I've seen it on other sites, too. Basically, you're loading the registers of the FM chip with some version of garbage, and the resulting sound has random and bizarre elements. Mine's a bit different. I liked the Tablehooters version that uses just a DIP switch for altering the data lines between the CPU and the FM chip for it's minimalism, but I hate the tiny tactility of DIP switches. Kevin's is nice but that's a lotta external hardware (does this make me less of a bender?). Anyway, I thought it might be nice to have a changeable but static scrambling mechanism for the data lines, keeping the mod clean and out of the way, and have the ability to change between sounds very rapidly by just pressing and holding one key. The Modification This mod's a bit involved. It requires two quad SPDT analog switches in sockets on a perfboard, quite a bit of soldering, and some dexterity with the iron, since mine ended up in a tight spot on the keyboard. Mine also used some "precision" drilling, gluing, etc. The circuit you’ll be implementing is this:



		How it works: the data lines that come from the CPU and go to the FM chip first are cut then routed through the mod. The mod bifurcates the data lines; one route goes directly to a throw of the analog switches and the other goes to one side of a component carrier. The component carrier can hold any wild routing you choose. The simple one that I used was just a bit shifter, where one bit is shifted to his neighbor. The other side of the component carrier (the lines in red on the schematic) go to the other throw on each of the analog switches. The control line on all of the analog switches is tied together to a single momentary button, which is nominally tied low through the 100k resistor. When the button is not pressed, the analog switches route the data lines to their correct pins on the FM chip, so the keyboard operates as normal. However, when the button is pressed, the analog switches select the data lines that are routed per the component carrier, and this is where it gets crazy. The way I've used it is, hold the button down while selecting the two digits of the voice, and you mostly get a voice that doesn't sound like it's name on the chassis of the PSS. As most others who've done this mod have stated before, the results can be unpredictable, and I've found this to be fairly true, too. I've also touched the component carrier with a wet finger while changing voice digits, as well as only partially loading the component carrier into its sockets - this increases the randomness of the resulting voice. The drums also get goofed by this mod, but generally you just end up with just the hihat, maybe a little crunchier than normal. Parts List one 16-pin wire-wrap sockets two 20-pin wire-wrap sockets Lots of short (2-3”) and longer (6-9”) strands of 30Ga Teflon-coated wire-wrap wire with stripped ends 6+ feet of 8-conductor ribbon cable (rainbow is best for good color-coding) two small scraps of perfboard: one to fit the 16-pin socket, the other to fit the two 20-pin sockets SPST momentary switch ~100kOhm resistor two MAX333 quad SPDT analog switches Um, don't ask why I used the MAX333's when I could have used the cheaper and more common CD4066. I think I was looking for really low ON resistance, but after I built it I revisited the specs and found that at the 9V supply, the two are not too different. Duh. Electrical & Mechanical Installation I don't remember all of it now, but basically: Get a 16-pin wire wrap socket and size it for placement in the upper outside corner of the keyboard (yes, it's going to be mounted on the OUTSIDE!) Mark and drill 16 holes, one for each of the wire-wrap terminals of the WW socket. While you're here, size and drill for the SPST momentary switch. Wire the teflon wires to the switch before inserting the 16-pin WW socket - you'll have easier soldering access that way. Insert the WW socket through the drilled holes and glue it in place (for extra mechanical strength, I used a piece of perfboard on the other side and bolted that down, too.) Prepare a ~6 inch section and an ~18 inch section of ribbon cable, by separating the wires about 1 inch from each end. Strip and tin all the conductors. After the glue is done drying, wire up the board with the prepared ribbon cable. Note: where I put it, this is VERY tight work with the soldering iron!!! Now wire up the board with the MAX333's on it, using a combination of wire-wrap and solder. Size it to be mounted "upside-down" in the top chassis. Mark the appropriate holes for the standoffs on the board and drill through the chassis Before mounting the MAX333 board, wire it up to the prepared ribbon cable from the 16-pin socket. Again, before mounting it, wire the MAX333's to the 18-inch prepared ribbon cable Over on the main PCB, cut the traces that go from the uP to the YM2413 FM chip. Now solder the other end of the 18-inch ribbon cable to the underside pins or traces of the FM chip on the PCB on the other side of the keyboard. Now take a 16-pin, 8-component DIP carrier and connect the pins on one side to pins on the other side in any routing you choose. I chose just a single pin offset (i.e., 1 to 10, 2 to 11, ...). That should be it for the installation.



		. My own comments about this mod: Performance: It's as others have said: fairly unpredictable but worthwhile when you find something bizarre. I like this one because it's pretty much holding down a single button, dial in the digits of a voice, and let go of the button. You can evaluate a new voice in just under 4 seconds! Further mods? Nah. This keyboard's just barely good enough for this much work. I actually really like the stock '04 Electric Piano' on this guy; some Wurli fuzz and decent tremolo.

Background

The Modification

Parts List

Electrical & Mechanical Installation

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Further mods?