Yamaha RX11 Repair Thread

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Rasputin
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Yamaha RX11 Repair Thread

Post by 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):



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!

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Re: Yamaha RX11 Repair Thread

Post by 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

Post by 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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Re: Yamaha RX11 Repair Thread

Post by dromer » Mon Jun 08, 2020 9:11 pm

A friend is sending me his broken RX11 that is at least missing the power transformer.

The service manual is a bit vague on the parts list (and half of it is in Japanese).
So does anyone know what kind of transformer is needed, should I try and fix it? ;)

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Re: Yamaha RX11 Repair Thread

Post by Rasputin » Wed Jun 10, 2020 7:40 am

dromer wrote:
Mon Jun 08, 2020 9:11 pm
So does anyone know what kind of transformer is needed, should I try and fix it? ;)
I am usually the first to advocate for repairing things (sometimes irrationally), but I would consider just parting it out. I'm a fan of Espen Kraft and all, but his claim that it is "one of the best drum machines ever made" is off-the-mark, in my opinion.

Sure... it's got individual outs and a few sounds to choose from, but the buttons tend to be super flaky and bounce prone, plus the sound ROMs cannot be hacked, so you're stuck with the same old boring sounds--an RX5, it is not.

It's instant 1984 in a box, though, if you're really about that and only that.

I guess one way to fix it would be to just ditch the PSU entirely and replace the power cord with a 15VDC wall wart power supply, and also add an LM2596 DC/DC buck converter to power the 5VDC rail. If you were going to do that, I would yank the EL backlight too and replace the display with an LCD with LED backlight.

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Re: Yamaha RX11 Repair Thread

Post by desmond » Thu Jun 11, 2020 9:19 pm

Rasputin wrote:
Wed Jun 10, 2020 7:40 am
I'm a fan of Espen Kraft and all, but his claim that it is "one of the best drum machines ever made" is off-the-mark, in my opinion.
I agree. Even at the time it was limited, being one of the earliest digital drum machines - it's dark sounding, inflexible, and completely out-shone by the machines to come a little bit later.

But then, anything retro these days is "cool". I mean, people seem to love the TR-505, which is a really poor, entry-level box that even at the time wasn't that appealing. Considering what you could do with it, at around that time I got the Kawai R50, which in terms of features absolutely blew the 505/626 range away, for the same sort of money.

I loved the R50...

(Oh, and yes, I picked up an RX5 some years back now as I'd always wanted one and they were the top of the range boxes around 1987. It was fun, quite interesting, has quite powerful sound shaping features and is very typically Yamaha to use but I ended up selling it again for something like 50 quid or so... I don't really regret it, and there's always the samples for some of that flavour - the kicks and snares are very recognisable...)

But the RX11/15..? No thank you... Vintage fetishism only goes so far, and it already goes way further than I'd take it - and I was around back in the day when they were current products...

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Re: Yamaha RX11 Repair Thread

Post by oortone » Thu Aug 20, 2020 1:23 pm

I have a RX11 and it's quite nice. No problems with buttons and stuff.

Anyway, just curious. What's the reason the sound chips is impossible to replace with Eproms?
Is it because of the ROM-chips themselves (pinout, electrical characteristics etc) or is it that the format of the ROM images is unknown and never reversed engineered?

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Re: Yamaha RX11 Repair Thread

Post by bibi p » Thu Aug 20, 2020 3:27 pm

My RX11 is acting weird, sending the crash cymbals on every step to my BeatStepPro sequencer. it used to work, not sure what happened. The hardware works on its own, but when I hook it up, the BStep triggers the crash cymbals on every single step regardless of the underlying pattern.

I have tried the two different resets to factory settings and toggling omni on and off, but it's not working. Any idea of what could be happening?

Thanks so much!

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Re: Yamaha RX11 Repair Thread

Post by Spydogen » Tue Oct 13, 2020 2:47 pm

Hi, thanks for your post and video.

I've got an RX11 that's started doing some weird stuff on the LED/LCD screen. Showing some JAPANESE characters, then just squares.

The drum pads are working, and (although I did the nuclear reset) there are moments when the screen will start working long enough (after a factory reset) for me to programme some new patterns.

Within a few moments, it goes back to Japanese, or just a blanked out screen.

Can you suggest anything to fix this?

Photos here :
https://photos.app.goo.gl/Zmf9zZMHKrwPmoyH7
https://photos.app.goo.gl/ZMWSwmvt5f79sFGa9

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Re: Yamaha RX11 Repair Thread

Post by Rasputin » Tue Oct 13, 2020 8:25 pm

oortone wrote:
Thu Aug 20, 2020 1:23 pm
What's the reason the sound chips is impossible to replace with Eproms? Is it because of the ROM-chips themselves (pinout, electrical characteristics etc) or is it that the format of the ROM images is unknown and never reversed engineered?
Numerous reasons: Custom ICs, can't easily be read, no writable equivalent, and they interface over a serial connection rather than parallel.

If someone was determined, I'm sure they could snoop the serial traffic and then put some modern microcontroller in there to deal with new sample data, but that idea isn't worth my time. Someone will do it eventually, I'm sure, just to do it.

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Re: Yamaha RX11 Repair Thread

Post by Rasputin » Tue Oct 13, 2020 8:27 pm

Spydogen wrote:
Tue Oct 13, 2020 2:47 pm
I've got an RX11 that's started doing some weird stuff on the LED/LCD screen. Showing some JAPANESE characters, then just squares.
It seems likely to be corrupt data being sent to the display because of a poor solder joint or header connection. The display is being initialized incorrectly or not at all.

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Re: Yamaha RX11 Repair Thread

Post by Spydogen » Wed Oct 14, 2020 12:29 am

Rasputin wrote:
Tue Oct 13, 2020 8:27 pm
Spydogen wrote:
Tue Oct 13, 2020 2:47 pm
I've got an RX11 that's started doing some weird stuff on the LED/LCD screen. Showing some JAPANESE characters, then just squares.
It seems likely to be corrupt data being sent to the display because of a poor solder joint or header connection. The display is being initialized incorrectly or not at all.
OK thanks, deffo looks a bit like too much solder on the pcb where it joins the connector +/ the loom that goes to the screen. Perhaps I'll redo that, or see if theres something making contact.

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