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#1546537 - 10/29/10 09:00 PM Problems with Yamaha MX100B with Disklavier
Rich H Offline
Junior Member

Registered: 10/24/10
Posts: 2
Loc: Delaware
We purchased a used Yamaha MX-100B (with Disklavier) last year and had it professionally moved and tuned once it arrived. It has worked fine since then, up until about 1 week ago. Part way through a playing a disk, the piano went silent and displayed "Piano Power Off - (PWM Over)!" If you power down and restart, it will again play partway through a song and display the same error. I'm curious if there is a simple fix for this or is it something to call out a pro for? I'm an electrical engineer with a heck of a background in "fixing" things, but without a maintenance manual or finding anything in the operations manual, I don't know where to begin. Any thoughts?
Richard A Holub

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#1547032 - 10/30/10 03:40 PM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
Dave Lotek Offline
Full Member

Registered: 12/31/06
Posts: 78
Loc: midwest
ftp://tech:disklavier@ Try this link, (copy & paste) look under service manuals. Hope this helps.

Edited by Dave Lotek (10/30/10 03:41 PM)
Piano Sales, Piano Technician, "Tuning pianos for a song"

#1548829 - 11/01/10 09:43 PM Re: Problems with Yamaha MX100B with Disklavier [Re: Dave Lotek]
Rich H Offline
Junior Member

Registered: 10/24/10
Posts: 2
Loc: Delaware
Many thanks. Found the error message and as I suspected, looks like it is going to be a power supply related issue. I always like to know the problem before I call in someone else - don't like not knowing what I'm asking someone else to do. Thanks again - I appreciate the link and the manuals.
Richard A Holub

#1628696 - 02/26/11 04:59 PM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
Marge Offline
Junior Member

Registered: 02/24/11
Posts: 1
Richard I have the same problem with my Disklavier MX100 II it will give me the same message Piano Power Off - (PWM Over)!" and will do the same if you restart it play one or 2 songs and stop did you ever fix the problem with yours thanks in advance Marge

Edited by Marge (02/26/11 05:04 PM)

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#1628910 - 02/27/11 12:18 AM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
pppat Offline
1000 Post Club Member

Registered: 08/09/08
Posts: 1203
Loc: Jakobstad, Finland
@Rich H: I have a limited experience with these instruments, but at least the one we host is exposed to similar problems - albeit randomly, but still. If you cure the problem by switching/repairing the power supply, please let me know.
Patrick Wingren, RPT

- - - -
Dedicated to learning the craft of tuning. Getting better.

#1993276 - 12/01/12 04:55 PM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
chrigi Offline
Junior Member

Registered: 12/01/12
Posts: 1
Hello I had the same problem and have solve it:

The power supply have a 20V-regulater (IC2 MJN78M20FA) witch is operated outside of its specification. At the entrance he receives 50V instead of the 40V allowed! Therefore, it switches off automatically.I put a strong Zener diode in series, so that it works with <40V.
Problem solved! smile

#1993329 - 12/01/12 06:17 PM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
David, OHIO Online   content
Full Member

Registered: 10/07/08
Posts: 213
Loc: Coshocton, Ohio
Check to see if the pedal solenoids are overheating. There should be pedal adjustment instructions on the inside cabinet. Sometimes the power error will be related and if the solenoid is too hot then it will terminate power to the system long enough for it to cool down to operating temps then you can prompt playback until it overheats again. Two cents.
David Chadwick RPT
Coshocton, Ohio
1931 Mason Hamlin AA
1935 Bush & Gerts Gr

#2161082 - 10/03/13 06:56 AM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
jaguar8888 Offline
Full Member

Registered: 05/13/07
Posts: 27
Loc: Sydney Australia
Hi everyone.
I know it's been a couple of years since this post, but I now have a similar problem.
I have an MX101R, which seems to be the Japanese domestic version of the MX100B.
Was working perfectly and then all of a sudden, it wasn't. Wouldn't even play from a floppy!
Sometimes it will start to play a MIDI file through Cakewalk, but then it gives up after only a few bars!
All the diagnostic tests 1-9 are OK except #7 the MIDI one, which has NG, even though the MIDI cable is connected. And the notes test #8 only plays up to note #30. (LCD says Get data = 55)
Re the MIDI test #7, you can't activate the MIDI switch with the red light wheh you start the test programme, because the + and - keys held together prevents you from doing that. And when the test in running, pressing the MIDI switch does nothing.
Any clues anyone? Is this related to the 40/50v problem above? How would I know if this is the case?
I don't get the "PWM over" error message though.
Ian Griggs
Sydney Australia

#2161083 - 10/03/13 07:03 AM Re: Problems with Yamaha MX100B with Disklavier [Re: jaguar8888]
jaguar8888 Offline
Full Member

Registered: 05/13/07
Posts: 27
Loc: Sydney Australia
The frustrating thing with the Service Manual is that it doesn't tell you how to address any of the NG faults!

#2610978 - 02/02/17 04:15 PM Re: Problems with Yamaha MX100B with Disklavier [Re: Rich H]
MikeOregon Offline
Junior Member

Registered: 12/03/16
Posts: 9
Loc: Gresham, OR
Has anyone had any luck with finding a replacement power supply for their Yamaha Disklavier piano? My MX100II power supply failed with several of the electrolytic capacitors leaking fluid and damaging the board. The unit is not viably repairable and Yamaha advised there is no replacement power supply available. It would be a shame to render this instrument, which I paid over $15,000 for, only partially useful.

I am hopeful that some combination of off-the-shelf power supplies and some custom circuitry could replace this.

Since a fine piano should be a viable instrument for many decades, I am disappointed that Yamaha has decided to drop support for this piano.

#2611744 - 02/05/17 02:35 AM Re: Problems with Yamaha MX100B with Disklavier [Re: MikeOregon]
Pro-TAC Offline
Full Member

Registered: 11/03/04
Posts: 79
Loc: Japan
I have power unit for Disklavier .(WC769209)
I'v confirmed that operation.
If you are interested, please sent me a private message.

Pro-TAC tuning and repair service.


#2612894 - 02/09/17 11:41 AM Re: Problems with Yamaha MX100II Disklavier Power Supply [Re: Pro-TAC]
MikeOregon Offline
Junior Member

Registered: 12/03/16
Posts: 9
Loc: Gresham, OR
I sent an email with photos of my power supply and details of parts I replaced. I'm looking forward to your reply.


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