Yamaha RX11 Repair Thread

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Yamaha RX11 Repair Thread

Postby Rasputin » Sat Jul 07, 2018 6:18 pm

I was slightly bored last night, so I wrote up some repair tips for the Yamaha RX11 - Digital Rhythm Programmer from 1984.

Sidenote: Remember when everything was a "drum computer" or "rhythm programmer" and not just a plain old drum machine? :lol:

Service Manual
First stop for repair jobs, of course. Courtesy of Elektrotanya (per usual): Yamaha RX11 Service Manual

Firmware
I believe only v1.0 exists, although it appears some RX11 revisions use dual ROMs for the OS instead of a single ROM. Either configuration is the same size program, so it doesn't really matter, but the single ROM version is more convenient.

The program ROM is actually a OTP ROM and not an EPROM.

Yamaha RX11 v1.0 OS ROM (program ROM, IC214) -- dumped by moi.

Non-Replaceable Chips (ICs)
Basically, if any of the Yamaha sound related ICs die then it's time to part out the machine or get parts from someone that decided to part out theirs because the wave ROMs (YM2190x series) and the RYP-4 music chip are very specialized. Be very, very kind to them.

Factory Reset
There are a couple "resets", but the most useful one is holding the STOP/CONTINUE and +1/YES buttons while powering on the RX11. If the battery dies then all manner of crazy things (inaudible voices**, invalid pan settings, clicking instruments, etc.) can happen because the RX11 doesn't re-initialize its own memory properly.

** Yes, it can appear as if the RX11 has hardware damage because pads will not sound properly (if at all) should they be set to an invalid instrument or if the panning gets set to 16 (which is impossible unless the battery backed RAM gets scrambled).

Holding STOP/CONTINUE and TEMPO on power-up will enter a self-test mode which has the side effect of not only a factory reset but killing all user data. This is the "full nuclear" option. You've been warned!

For more info, visit this excellent page: http://www.wolzow.com/analog/rx11-test-reset.htm

Factory Patterns
As the factory patterns were only stored in RAM and not ROM, unless someone did a SysEx or cassette tape dump of them, the only way to get them back in the RX11 is manually. :(

Yamaha RX11 & RX15 Pattern Booklet

If anyone ever actually keys all this in, please do export it digitally and share it!

Button/Switch Repair (Mechanical)
Basic "clean out the dirt, dust, grime, and corrosion" switch repair (and teardown):

Watch on youtube.com


Button/Switch Repair (Electrical / Key Matrix)
Each panel button is the intersection of an S-signal and a B-signal. When the CPU detects Bx (x being the number of a particular signal) is active due to a button press, the CPU compares Bx to Sy (y being the current line being strobed by the CPU) and checks to see what button lies at the point of intersection between Bx and Sy.

Whatever button lies at that spot in the key matrix is then detected as being pressed.

Ex: FUNCTION is in S3 and B0, so if the B0 circuit is closed when S3 is currently energized by the CPU (via IC221) then the CPU knows FUNCTION is currently being depressed.

Signals S0~S5 are supplied from the mainboard by IC208 (HC138) via the CN203 connector on pins 1~6 and are received by the panel board at CN1 over a flat cable.

Low Resolution Color Coded Diagram of S-Lines (preview only):
Image

Download - High Resolution Color Coded Diagram of S-Lines (this took a lot of work, so I hope someone is illuminated by this chart!)

S0 [CN1-1]
TEMPO, -1/NO, +1/YES, ACCENT, ACCENT LEVEL, STOP/CONTINUE

S1 [CN1-2]
PATTERN/SONG, REALTIME/EDIT, STEP/INSERT, COPY/DELETE,
SWING/REPEAT, QUANTIZE/TEMPO CHANGE, CLICK/CHAIN, CLEAR

S2 [CN1-3]
7/INST CHAN, 8/MIDI IN, 9/MIDI OUT, PAN, INSTRUMENT LEVEL, START

S3 [CN1-4]
FUNCTION, 0/SYNC, 1/CASSETTE, 2/CARTRIDGE, 3/SAVE+VERIFY
4/LOAD, 5/FORMAT, 6/INSTRUMENT OUT

S4 [CN1-5]
SD 1, TOM 1, TOM 2, BD 1, HH OPEN, RIDE, COWBELL, SHAKER

S5 [CN1-6]
SD 2, TOM 3, TOM 4, BD 2, HH CLOSED, CRASH, RIMSHOT, CLAPS


Signals B0-B7 are the second half of the key matrix. Supplied by the mainboard by IC221 (40H240) over CN203 pins 7-14 via a flat ribbon cable to CN1 pins 7-14.

B0 [CN1-7]
SD 2, SD 1, FUNCTION, 7/INSTRUMENT CHANNEL, TEMPO, PATTERN/SONG

B1 [CN1-8]
TOM 3, TOM 1, 0/SYNC, REALTIME/EDIT, 8/MIDI IN, -1/NO

B2 [CN1-9]
TOM 4, TOM 2, 1/CASSETTE, STEP/INSERT, 9/MIDI OUT, +1/YES

B3 [CN1-10]
BD 2, BD 1, 2/CARTRIDGE, COPY/DELETE

B4 [CN1-11]
HH CLOSED, HH OPEN, 3/SAVE+VERIFY, SWING/REPEAT

B5 [CN1-12]
CRASH, RIDE, ACCENT, INSTRUMENT LEVEL, 4/LOAD, QUANTIZE/TEMPO CHANGE

B6 [CN1-13]
RIMSHOT, COWBELL, PAN, ACCENT LEVEL, 5/FORMAT, CLICK/CHAIN

B7 [CN1-14]
CLAPS, SHAKER, 6/INSTRUMENT OUT, CLEAR


Display Replacement / Upgrade
The stock display is a standard LCD 16x1 HD44780 type character display with EL foil (requiring high voltage backlight inverter). Although the pinout and dimensions are standard, replacing this display is somewhat problematic as the RX11 display mounting posts are too short for modern LCD character displays with LED backlights; the LEDs are thicker than EL foil.

Also, the header for the display cable either needs to be removed from the original display (professional desoldering required) and soldered onto the replacement display, or the end of the display cable will need to be cut off so the bare wires can be soldered directly to the replacement display.

The solution for the short mounting posts is to use slightly longer screws -- #4 x 3/8" screws will work here. The mounting posts are plastic, so be gentle and only tighten the screws just enough so the display doesn't wobble around. You could also add shims, etc. if you want to adjust the viewing angle a bit.

Note: There is a contrast trimmer pot on the RX11 mainboard, so tweak to taste once the display is installed and working.

For fun, I decided to go with one of those cheap 5V 16x1 buydisplay.com eBay LCDs in "negative black". "Black" here really means more like "midnight blue", so it's not as aesthetic as one would hope.

I decided to put a 330 ohm resistor between pin 2 and pin 15, and a straight jumper between pin 1 and pin 16 on the display to provide power for the backlight.

An OLED fitting those dimensions would be much more satisfying, honestly, but just about anything is a step up from the weak stock display.

Random Thoughts
Stop/Continue button cap can be swapped with Accent button cap. Now swap Start and Stop/Continue button caps. Start will be green, Stop will be red, and all four blue buttons will be at the bottom left. Makes so much more sense this way!!!!

:wink2:

Also, the crash sound is way too loud. I have its instrument level turned down to 01. Ridiculous!
Rasputin
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Re: Yamaha RX11 Repair Thread

Postby Periphery » Mon Jan 07, 2019 7:45 pm

Wow, amazing job Rasputin!

This is my first post here. Joined because I saw this thread hoping that you'd maybe shed some light for me seeing you seem to know your way around these Drum Computers!

I just bought a Yamaha RX 15 (Today) and it has the trigger problem where the samples are triggered several times and that's something I can do something about.

But I only have the left output working. When I plug my headphones into the phones-output it only plays from my left cup. The right output doesn't work and the left output works. What could this be? I read somewhere that there's a function where you can select if the pad/sample should play in stereo or not. But I'm unable to find such a function on the RX15.

Do you have any idea what it could be? It seems like there's two LPF after the DAC. Could one of them have given up?

Thanks in advance!
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Re: Yamaha RX11 Repair Thread

Postby Rasputin » Tue Jan 08, 2019 6:23 pm

Periphery wrote:But I only have the left output working. When I plug my headphones into the phones-output it only plays from my left cup. The right output doesn't work and the left output works. What could this be? I read somewhere that there's a function where you can select if the pad/sample should play in stereo or not. But I'm unable to find such a function on the RX15.


Assuming you've reset or re-adjusted the pan for each instrument and you've still got this problem then I'd venture it's a hardware issue, especially since it presents on every single instrument.

If the right channel for both the headphones and also the main outputs does not work then that indicates it's probably not a jack issue.

I'm not intimately familiar with the RX15, but I believe most/all of the stereo-only models of that Yamaha vintage like the RX7, RX15, and RX21 (RX21L) use a single 8-pin dual op-amp to drive the audio outputs.

Look for a small (but not tiny) DIP-8 chip by the output stage possibly labelled NJM4556D, YM4556D or similar. If so, Pin 1 and Pin 7 are the audio outputs and ultimately connect to the main output jacks. Pin 2 and Pin 3 are paired as one input channel, and Pin 5 and Pin 6 are paired as the second input channel.

If Pin 2/3 and Pin5/6 are supplying signal, but either Pin 1 or Pin 7 (Pin 1 is left output, maybe?) is dead then the op-amp is very likely at fault. If Pin 2, 3, 5, or 6 are not supplying a signal then you may have a more serious problem like a bad DAC.

I don't have an RX15 nor the schematics/service manual, so it's hard to say with any certainty, but that's my best guess at the moment.
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