What type of sustain pedal Roland EP-90 digital piano is using - open or closed at rest?

This wish an after market pedal, or the original 3's connector? If the keyboard is on when you plug and unplug that, it is likely due to a voltage reference getting confused. Usually when you get constant sustain then most likely a switch is stuck closed, or open, down there in the pedal. How these things work normally is that a pliable switch is opened, for sustain, or closed. It depends on the keyboard. Some keyboards have a setting inside them to accommodate both types of pedals, and some pedals have a switch to choose either. Your keyboard does not have a setting that I can tell, other than adjustments for a resonance option (nice feature). I am not sure the newer RPU-3 pedal is compatible, it seems to be for the newer models. If you are handy with a volt meter, then can check the cable's pins for a common, then a pin that changes with each pedal (use continuity mode, beeps when circuit is closed). Could be a piece of dust is in there, or hair or carpet stuff, and a good cleaning would fix that from blocking the normal function. Manual Link: http://media.rolandus.com/manuals/HP-237_OM.pdf

Yep... Roland pedals are reversed, that is, normally closed contacts. Unlike some Yamaha keyboards, the Casio doesn't have an inversion function available. You have two choices to solve this: 1. Buy a pedal with the corect sense 2. Open the Roland pedal and MAYBE with a soldering iron you can move a wire to select a contact with the opposite sense.

Sorry, but the Yamaha pedal has the opposite sense (it is a normally open contact) than what is REQUIRED by Roland equipment. Roland requires a Normally Closed contact. Unfortunately, one is confused because the Roland jack for the sustain shorts itself to no sustain when you unplug a pedal. SOMETIMES one can open a pedal and with soldering iron change a wire to reverse the pedal sense IF the particular pedal has both contacts available.

I you mean the sustain type pedals, FIRST check the connector(s) as they often come loose or unseated. Next check for a broken pin in the connectors. It is UNLIKELY you could troubleshoot anything inside with just a meter. It appears that some of the Roland pedals receive 5 volts in the connector, and upon contact closure the voltage is sent back to the piano where it drives C4570 buffers with 680K to ground and an RF bypass cap and series 330 ohm to the + of the C4570's. The circuit I have is for a different piano but if yours uses the 8 pin connector it is likely the same.
The contact is actually optical interrupter modules with a driver transistor. There are threshold setting pots in the pedal assembly as well. The farthest I would suggest you go is to make sure the optical interrupter modules are free of dust if this is the type you have,.

This is confusing... you say "the sustain works when you disconnect the cord"? How can that happen? and doesn't work when it is plugged in.

MOST sustain pedal problems are due to people using a different pedal than the keyboard is designed to use. It is very common that someone tries to use a Roland sustain pedal on a Yamaha and oof course it doesn't work because the Roland pedal is normally closed and Yamaha usually requires a normally open contact.

A FEW keyboards now check the state of the pedal input when power is first turned on and configure the pedal polarity accordingly. For these keyboards, make sure the pedal is plugged in before power is turned on.

I assume you are plugging this into a ROLAND brand product as the Roland sustain uses a normally CLOSED contact while MOST other brands use NORMALLY OPEN contacts.

The Roland synths now monitor the pedal as the power is turned on and supposedly decides which contact type is used.

Remember that for MANY voices, such as piano, notes are held longer BUT they do not continue indefinitely just like the sustain on a real piano works. On a real piano the dampers are lifted, but the strings eventually stop ringing due to the losses of energy in the strings.

Some voices will be held,such as organ tones.

I don't have enough information from your post regarding what voice you are having trouble with.

The answer is NO... Roland uses the opposite sense switches on foot pedals... They use NIRMALLY CLOSED and your Yamaha is a NORMALLY OPEN switch.

SOMETIMES you can open these pedals and find that the pedal has the opposite sense switch available and you only have to unsolder and move one wire to make it a NORMALLY CLOSED pedal.

You MAY be trying to use a Roland pedal on an instrument that requires a different one.

The Roland have a normally closed contact where MOST others are normally open.

If you are using Roland equipment, then use of another brand OR a broken cable will cause this as will a shorted cable with other brands.

It looks like you MIGHT have a Technics given that number you posted. Not sure of which polarity pedal you require with that, So you need to test it.

Plug in a regular instrument cable and see if it sustains with nothing at other end. If it does, you need a normally closed one.

The ROLAND pianos USUALLY require that you use a normally closed sustain pedal.

MANY pedals are the opposite and close when pressed. SOMETIMES you can open the pedal and reverse the way the switch works.

There are two types of damper pedal switches, on that is closed until you press it, and one that closes when your press it. It sounds like your Casio is expecting one type and your Roland pedal is the other type. A quick way to test this is to plug a guitar cable into the Casio pedal input and see if the keyboard sustains. If it does, then your Casio requires an "normally closed" switch.

Some pedals have a small switch near the cord or even on the bottom of the pedal that will reverse the switching operation (BOSS pedals, a division of Roland, have this feature). If you can find that, then change the switch position and you should be OK.

If not, and you feel like digging into your pedal, you could take the bottom off of the pedal and check out the switch itself. Many pedals use a switch that can be used either way. The clue will be on the switch itself. If there is an extra tab on the switch that is unused, then switch the wire that is furthest away from that tab to that tab. This will probably involve soldering, but it is nearly impossible to damage anything.
If moving the wire that is furthest away does not do anything, then try putting that wire back and switching the other one.

If your pedal does NOT have an extra tab, you're SOL, unless you want to buy a replacement switch (unsure of make). If this is the case, you are probably better off getting a different damper pedal - preferably one that is marketed as "universal"