Yamaha Motifxs6 digital keyboard doing weird things.

Thread Starter

Yami

Joined Jan 18, 2016
242
Hi everyone,
Recently I got a Motif xs6 in for repair. The customer complained about some of the notes sustaining even after the key has been released. When it starts to happen it effects all the keys in all the octaves. For eg: All the C's and F#'s all octaves. It needed some other work done so I completed all of that and then powered it on to check it out.
The first night I tired it was working perfectly fine. Then I went into service the keybed as the whole thing was in pretty bad condition. The keybed was exceptionally bad the solder joints were crummy and black in colour. I cleaned the whole board with Isopropyl alcohol. Put everything back together and powered it on. The problem started. Keys sustaining and the effected keys sound very loud. I took some voltage measurements and it clearly showed that the keyboard "thinks" that notes are pressed even after the key was released. I measured at the diodes and it normally should show 5V not pressed and something below that when it is pressed.
Any way my thinking was 'bad connections!'. So I RE-SOLDERED all the connections (more than 200!). It almost looks new now.
Again I put everything back together. Now the voltage measurements looks fine, but now what has started to happen after sometime only one key starts to go mad. There is a delay in registering the key press sound comes way too late when the key is pressed. It might get loud all of a sudden.
I was hoping that some one could help me figure this out. I have downloaded the service manual but it only shows how disassemble the unit and names of the IC used etc. It doesn't show any test point measurement details or anything like that. There are two VR on the keybed circuit board named 'Gain' and 'Offset' the manual doesn't specify what it is and how it should be set.
Here is the link for the service manual.
https://www.synthxl.com/yahama-motif-xs-6/
This is quite an important project for me. Hope you guys could help me out.
Thanks in advance.
 

MRatton

Joined Sep 25, 2019
5
The most common problem in musical instrument keyboards is bad contact of the rubber contact and the board contact. So, the first thing to do is to clean the board contacts on the board. But in the case of the rubber contact, the problem in general is due to waste of the contact material, so it is not possible to solve cleaning it (in fact, if you try to clean the rubber contact it will become worse). If so, you will have to replace the rubber contact strip.
But as you describe, it seems that the problem affects various keys in a systematic way. As the key contacts are arranged in a matrix arrange, maybe the problem is due to an IC failure, in the IC that scans the contacts.
 

bertus

Joined Apr 5, 2008
20,328
Hello,

The keyboard connections are shown on page 249 of the PDF.
The C and F# are on lines MK0[5] and MK1[5]
They are connected via a flat cable to the CPU.
I have taken some snapshots of the PDF to show the details:

MOTIF_XS_c_Fsharp_connection.png

MOTIF_SX_connector_cn5_cn1.png

Perhaps one of the connectors is failing.

Bertus
 

Thread Starter

Yami

Joined Jan 18, 2016
242
@bertus , @MRatton thanks so much for the help. The key bed board is as clean as it could be at the moment. I was very careful with the carbon contacts. I didn't use any alcohol on them just wiped it with a clean brush.

I wanted to share some voltage measurements I took which look kind of odd. I might be onto something but I can't figure out where the problem is and how to fix it. Anyway I took DC voltage measurement from the pins to ground shown in the schematic. Some pins measured 5.03V as expected, however some pins measure something around 4.73V (doesn't look bad I guess) - but whats interesting is that the pins which shows lower voltage, when measured in the AC voltage setting shows significant AC ripple! Something around 0.5Vac, compared to around 13mVac measured on the good pins.

What could this mean? How could I further diagnose it?
Thanks again for the help.

MotifXS6.jpg
 

MRatton

Joined Sep 25, 2019
5
Hi, Yami,
Try to make the contacts manually, directly on the board contacs, or exchange the rubber strips, to check if the problem changes.
 

Thread Starter

Yami

Joined Jan 18, 2016
242
Hi, Yami,
Try to make the contacts manually, directly on the board contacs, or exchange the rubber strips, to check if the problem changes.
Yes sounds like a good idea, but the voltage measurements were taken without pressing the keys. So I suspect its do with the IC, maybe an electrolytic cap failed? Hard to figure out where this could be though :S..

Thanks
 

absf

Joined Dec 29, 2010
1,942
Here's the block diagram of the whole keyboard..
yamaha block diag.PNG
You can see btw the keyboard and the main board (DM), there is nothing but just wires connecting them. Actually there is another interface board there which was not drawn.... the EMKS-FD board.

If the problem is not due to rubber contacts, then the most suspected board is this one.. This board just consisted of a 64-pin MCU and a dual op-amp for the after-touch effect function. It interfaces to the DM's e-Bus (7 pin).

see attached.

Allen
 

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Thread Starter

Yami

Joined Jan 18, 2016
242
Here's the block diagram of the whole keyboard..
View attachment 187055
You can see btw the keyboard and the main board (DM), there is nothing but just wires connecting them. Actually there is another interface board there which was not drawn.... the EMKS-FD board.

If the problem is not due to rubber contacts, then the most suspected board is this one.. This board just consisted of a 64-pin MCU and a dual op-amp for the after-touch effect function. It interfaces to the DM's e-Bus (7 pin).

see attached.

Allen
Hi Allen, Thanks for the response. Yes the board which is connected to the keybed right? Just below it. That is my primary suspect too, but I am wondering what could be causing this behavior - which component could fail to give this kind of response as some of the keys are working fine.
Could you please suggest on what to look for :)

Thanks so much
 

MRatton

Joined Sep 25, 2019
5
Press a C and a F# and check with the scope the signals at MK15 and MK25 on CN1; then compare these signals with another bus where the keys are ok.
 

Thread Starter

Yami

Joined Jan 18, 2016
242
Hi everyone, potential breakthrough!
I was able to borrow an oscilloscope from someone but its a handheld one (30Mhz bandwidth).
Picture 1.jpg
Here is the result I got:
1.Probe at BK00 ..... BK07 - I get a clear on and off sweep from all the pins with exactly same on and off times except for BK00 - the off time was slightly longer compared to other BK pins.
2. Probe at MK10 .... MK25 - these pins were a bit weird! With some pins I got sort of a square wave with slight 'rounding of the edges', and with some pins I just get a straight 5V line. This is without pressing any keys.
When I pressed the corresponding notes I get sort of spikes which goes down, in both the 'square wave' and 'straight line' pins.
I hope I'm on the right track.
I suspected it to be the electrolytic caps failing near the ICs but I didn't measure any ripple on the VCC etc.
Now my prime suspect is the small caps on the EMKS-FD near the connector. Picture 2.
Picture 2.jpg

Thanks so much for the help. I hope you guys could advice on me what to do next, and help me figure this out.
 

absf

Joined Dec 29, 2010
1,942
I've never repair the EMKS board up to component level. Just replaced the whole board as it was not expensive. I remember replacing one EMKS board for the PSRS series keyboards and it only cost $15.00 then. The board uses a 44 pin mcu plus some passive components.

Good luck with your trouble shooting and hope to hear good news from you soon.

Allen
 
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