Hi everyone,

I want to explain how I find out this forum and why I decided to post here with a shot story.

I got in possession of a broken Yamaha P-95 keyboard that was in the street, brought it to home with me, bought a power supplier.
Gladly, it was working, but it wasn't producing any sound.

So with an online research I came across this community, changed the broken electrolytic capacitor as suggested as in this thread and the piano started to sound again!

Now, I am not practical with electronics (I am reading an electronics for dummies as recommended by someone). Soldering the cap it has been my first experience with this world, so I decided to subscribe here to asking you if your expertise could help me.

I got a 3 pedal unit with a 5 Pin DIN that is incompatible with my keyboard. The seller didn't want it back and just decided to refund me.

The P-95 uses a 6 Pin DIN (it looks like a PS/2 connector to be honest).

I was wondering if there is any way to convert the circuit into a compatible version for my piano like an LP-5A pedal unit (which it looks like it doesn't use any potentiometer, even if is not specified in the schematic below which model of pedal unit is).

The circuit, called CB-JT1 has three switches (SOFT, SOSTENUTO and SUSTAIN) that are sharing what I believe to be the GND (D).

SOFT belongs to pin Z, SOSTENUTO to pin H and SUSTAIN to L.



At the beginning I tested the board with a teensy 4.0 (here you can see the video https://streamable.com/d86wtc) and used a potentiometer to emulate the Sustain Pedal FC3A, a pedal that connects to the piano through the jack input (here there is a teardown on reddit).

I was convinced of using a pot for the SUSTAIN switch because of what I saw on Reddit, so I proceeded to interrupt the copper trace of the SUSTAIN switch to avoid interferences with the pot. And added some soldering in case I had to solder the wiper, ground and VCC to the board.

However, according to the service manual of the P-85 (it looks like the P-95 and the P-85 are sharing a lot in common inside), the 3 Pedal Unit uses 3 switches and zero pots. So the test with the teensy has been a waste of time.



I believe the pedal unit I got uses a Normally Open switch that needs to be closed to send signals to a keyboard (or at least it how it was working with the teensy).

Now I am not sure if it has to be Normally Closed, and it has to be open when I want to send an input for the P-95.

Is there a way to convert this circuit like above in something that could work for my keyboard?

 

IF the keyboard that you have actually has the functions that the tripple pedal is intended to control, then there is a chance. BUT what is posted shows only switches, no variable resistors (pots) So the switches are for ON/OFF control of something.
IF we had a circuit schematic of the circuits being controlled it couldavoid a lot of guessing.

 

IF the keyboard that you have actually has the functions that the tripple pedal is intended to control, then there is a chance. BUT what is posted shows only switches, no variable resistors (pots) So the switches are for ON/OFF control of something.
IF we had a circuit schematic of the circuits being controlled it couldavoid a lot of guessing.

Hello MisterBill2, thank you for your reply.

This is what I got from the manual service:




I checked on the internet if there was somebody who opened the LP-5A just to be sure if the board is just a switch controller, but I had no luck

 

Little update:

Reading the manual, it looks like the board is this one, a WJ983300.

The product compatibility listed in this website for the Yamaha YDP-S30 confirmed that is compatible with a P-85 (so this confirms that is compatible with my P-95) and that is compatible with the LP-5 unit:

https://bel.4567.cz/en/eshop/switch...w5MyIUe4xfD19bRlQ5Hwq1swuYJBJS0qdPhQw6XVp9W0F

It looks to me that the board has only three switches (the same as the schematic in the manual service, but the traces on the board in the image are confusing me!)

I don't understand how it could simulate the full and half damper when pressing it without a pot

 

I don't understand how it could simulate the full and half damper when pressing it without a pot

Could be that the third silicon button has different heights when you are pressing half pedal for the half damper to activate the first switch and pressing it at full activates both switch and the keyboard emulates the full damper?

 

Hello,

This kind of switches have pieces of carbon impregnated parts, that make contact with the pcb traces when pressed.
If the supports for the carbon pieces have different heights, the longer support will touch the pcb earlier than the shorter support.
Have a look inside the silicon part to see if the supports have different heights.

Bertus

 

Hello,

This kind of switches have pieces of carbon impregnated parts, that make contact with the pcb traces when pressed.
If the supports for the carbon pieces have different heights, the longer support will touch the pcb earlier than the shorter support.
Have a look inside the silicon part to see if the supports have different heights.

Bertus

Rather than try to look inside the switch, which may be a challenge, simply use an OHM METER across the plug that goes into the amplifier. THAT is a lot easier and will give a correct answer without risking damage to the tiny switch in the pedal package.

 

UPDATE:

Hello guys, there is an update. I managed to copy the original LP-5A behaviour with the free three pedals unit I got.

I quickly restored the CB-JT1 board similarly to the way it was when I opened the pedal unit just to start it over:



The LP-5A is a circuit board with 5 connections, while the CB-JT1 is a “castrated” circuit board because it isn't compatible with the P-95.

The LP-5A uses two switches for the half and full damper status, so, I interrupted the trace at the bottom to obtain two switches for the sustain function. In this way, I obtained a fifth connection, with 4 switches in total:



Then I soldered a DuPont connector to that switch, to create the fifth input for the cable and glued it under the board:





Here I was testing the connections before doing the soldering:



Then I used an old Ethernet cable and a PS2 connector and soldered everything:



To get the first status of the Half Damper, I added a piece of wood in the hole of the silicone switch. When I press half of the pedal, it touches the switch at the bottom simulating the half damper:



Here there is a quick test I did to verify that everything is working:

3 pedals unit converted test (the noise you hear is not from my piano, but from the phone)


This is the RearControlMIDI plugin log in Reaper that recognises the three pedals connected directly to the piano:



And this is me at the end of the day after one wasted morning trying to solder the 6 pin din connector:

https://media1.giphy.com/media/v1.Y...F9naWZfYnlfaWQmY3Q9Zw/lnlAifQdenMxW/giphy.gif

Thank you!