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Photos Of Naked Model On The Internet!

Yesterday I decided to take our Yamaha P120 apart. My interests were two-fold. Mainly, like any engineer worth his salt, I wanted to peer at the guts inside, write down some chip numbers, and look up the parts on the web - level one reverse engineering. But I also wanted to do my part to push any visiting techs over the edge into a nervous breakdown, so I'm sharing some photos of it here in this public forum.

I took it off the stand and set it on the studio rug on it's back. The application of one Philips screwdriver over a 10 minute time span and the dirty deed was done. Our Yamaha P120 laid bare before my eyes - make love to the camera, baby!


Here is the P120 disassembled. It turns out you really only need to remove the screws to the back section, not the sides or the front. The back section slides into slots in each end piece, to remove it just slide it back and then lift up once you hit the end of the slots. The left end holds all the connectors (a rather awkward and unfortunate design decision IMO). The whole deal is supported by a slab of aluminized MDF on the bottom.


A view to the left side of the guts. Here you can see the main processor board and the left speaker. Lots of wires. Must be somewhat labor intensive to manufacture.


A view to the right side of the guts. Here you can see the audio amplifier board (nice heatsink) and the right speaker. The speakers are rated 10W / 20W max. and as you can see are unfortunately not acoustically contained in any way, just flopping in the breeze. They actually point out the back of the DP, with a slot in the top permitting the backwave to reach the player. Pretty odd all around. Sounds about as good as you might expect for such an arrangement (i.e. not too good).


A better view of the processor board. You can see the wire harness to the keyboard, and a large RF-reducing ferrite doing double duty as a wire anchor. The upper board holds all the control buttons and blinking lights and stuff.


Key mechanism in the key-up position. Yamaha uses rods bent in a hairpin shape for the weight. You can kind of see the leaf spring there too.


Key mechanism in the key-down position.


On the audio board heatsink I discoved this IC:

LA4705N - 15w 2-channel Power Amplifier

And here are some of the parts on the main board

CY62256LL-70SNC - 256K (32K x 8) Static RAM
OKI MSM514260E-60TK - 256K x 16 DRAM
PCM69AU - Dual D/A, 18-bit
Yamaha X201110 - house numbered, most likely flash
Yamaha X201??D - house numbered, most likely ROM or key scanner
Yamaha ??947C0 - house numbered, most likely ASIC
TD62785F - Transistor array (8x)

I'm kind of surprised they apparently use ASICs as processors, they must make tons of these. Too bad the flash is house numbered, I would have liked to have known the size of the sample storage. Couldn't find any soul to speak of.

Afterward I buttoned it back up and checked all the keys - it seems no worse for the peek at the internal organs.

The keyboard looks mostly the same as the GHE/GHD in my CVP96.
The keyscanner is a single prozessor chip 40 pin DIL and is on the PCB that is beneath the keys. (when it is the same as I had seen)
If I counted correctly, there are 8 wires. Thats not enough for VCC,GND and 88*2 switches to decode, so it is probably the same ;-).


Did you check if the hammers can move independently from the keys? (I dont believe so)

For further questions ask here for the service manual.
http://www.wdgreenhill.com/

They have much more than listed, ask.
You get legal paperware only, no pdf's.

;-)

Peter

Thanks, Dewster. Nice photos. Always interesting to see the inside of these machines . . .

They don't need to monitor all the keys at once. They scan the keys. Basically they ask each key switch in turn "are you closed?" Then the switch can report it's state using a "party line" shared by all the 88*2 switches.

Agreed - thanks for the pics dewster.

Do you know approximately when this instrument was manufactured? It would be interesting to compare the internals to the P140 which I believe replaced the P120, then the P155 which replaced that.

Hmmm...I wonder why Yamaha chose to name the product P155 - P160 would surely have been the more logical progression, albeit potentially confusing with the YDP-160.

Cheers,
James
x

I've never really understood the numbering of various models of various manufacturers. I suspect that they've got a bunch of number and letter combinations on a giant dartboard. When it comes time for a new model, they throw a dart.

Good eye! Yes that's 8 wires going to the keyboard assembly. I believe the key scanner chip is a 48 pin DIP right there on the main board (interesting that it is socketed):



Maybe they use diodes and multiplex the heck out of it? Or perhaps there is a scanner on the key assembly and it sends serial (MIDI?) data? I should have investigated that more closely.

I didn't think to check the mechanical independence of the hammers, though I did take a movie of pressing a key, see what you think:

http://www.mediafire.com/?enjlzmowwz2

Thanks for the link!

There's a chip in there with 2001 marked on it if that means anything. Perhaps the serial number has the date encrypted in it somehow, or there is a table of what serials were manufactured when somewhere?

Fantastic breakdown of the keyboard dewster!



It doesn't surprise me that an instrument of this vintage has an ASIC. My guess is that there's probably a fair amount of full custom DSP to provide all the goodies including real-time effects with low latencies. They weren't going to use FPGAs of that era (nowhere near dense enough for the cost), and off-the-shelf DSPs were powerful enough but probably more expensive per unit than the ASIC (even considering ASIC NRE) and possibly more hungry for both board space and power. That's not including other things like the main micro, peripheral interfaces, etc. which they could do with an ASIC. Off-the-shelf System-on-a-Chip was still getting its legs at this point and was definitely not targeting this application.

Once again, hat's off to you for a great review!

The P-120 wasn't one of Yamaha's better moments...you'd be better off trading it in on a Roland RD-700 GXF...they look much nicer when taken apart...

Snazzy

Snazzy, would you care to elaborate?

Cheers,
James
x

No need...Dewster is doing fine.

Snazzy

What have been the highest selling Yamaha boards in the past? Anyone know the numbers?

This one of the two keyboard - contact PCB's taken from CVP96 SM.
Because it has a quartz, it is probably a single chip CPU that actively scans and debounces the contacts and initiates interrupts and sends serial data to the main CPU.

I think this 40Pin DIL visible on your photos scans and multiplexes the front panel switches and LED's.

Yamaha's DX7 keyboard synthesizer reportedly sold 160,000 during the 80's, according to Keyfax 4.

Korgs's M1 has allegedly surpassed this figure (Keyfax 4 again).

Best selling piano was supposedly the P-250 (2002) from what I hear.

Snazzy

I think their design is more sophisticated than you give credit. I think they assume the piano will be placed up against a wall. They are using the wall, the internal volume of the P120 case and the slotted opening to shape the sound. They do a good job considering the very low cost parts used. It actually would have been easier for them to mount the speaker cones facing up and cut a speaker grill in thetop of the piano case. But then it would really sound like a toy piano.

There is enough room inside for you to "hot rod" the audio section maybe with some full range Fostex drivers and a better amp.

I've seen some pretty amazing stuff done with low cost parts. A decently flat mid-bass driver, a paper cone tweeter, an electrolytic non-polar capacitor, maybe a sandblock resistor, and a coil if absolutely necessary, all can be had for $10 to $15 per side retail. Put that in a proper sealed or ported enclosure and it can sound like way more than you paid for. But here all they have is an oval speaker, and they point the back of it at you through a slot in a big leaky box. They're not even trying.


The flattest FR is almost always from the front of the driver on-axis. The backs of these speakers point into the entire cavity of the DP, which isn't sealed by any means. The L & R speakers even share the same acoustic space. In this leaky space the slot can't have any real tuning capability as in a ported enclosure. In such a scenario the main thing the backwave emerging from the slot would do is cancel out the frontwave, producing anemic bass. It's pretty clear Thiele & Small weren't consulted for this design.


It really could use a better set of sounds too, so beefing up the audio would be a diminishing returns thing. Easier just to buy something new with no built-in speakers as we're already using an external amp.

fascinating stuff... except i won't take my p155 apart.

<--- is hyperventilating.

This is my favorite thread for all week. Loved the pics, and the commentary just as much. "make love to the camera, baby" [snorts with laughter]

Interesting. They have 15 banks of 12, which gives 15 * 12 = 180.

180 / 88 = 2.0455

So there are two switch contacts per key, correct?

The XCK / ACK looks like some kind of handshake, S0 could be serial out. Series resistors on the outputs for signal integrity. And I agree that the crystal strongly implies a processor, particularly that humongous DIP.