My Roland HP-1800 is 13 years old, and recently, only occasionally, hitting middle-C with normal mF force has it sounding at FFF. The problem is highly sporadic, and volume-by-velocity is still variable - just much, much louder than the keys around it. It usually returns to normal.

I do not fully understand the mechanism on an older digital piano like this. I understand the two main mechanisms are velocity detection by light-beam crossing or by conductive membrane impact. If it is the former, a crack or debris could create false reads. If the latter, maybe it could just be worn out.

I'm not a piano tech, so would very much appreciate input from anyone who might know, esp. a remedy!

Thanks in advance.

I'm not familiar with that model but judging by the age I think it's most likely it will be a leaf switch. This type consists of 3 strips of copper with contacts on them.

It sounds like you are willing to pull the piano apart. If so I suggest you check to see if the switch is bent or possibly sticking where it interfaces with the key. The contacts may also be worn out which will mean replacing the key contact strip for that block of keys.

Bare in mind that there is probably exposed mains voltage inside so unplug it before you start to take it apart and be very careful that you get it back together correctly.

Thank you Mike! That helps quite a bit. I'll have a go at it.

HOW TO FIX REPAIR ROLAND HP-1800 ROLAND HP1800 LOUD KEY

I have mitigated the problem - Middle C plays normally now.

I am posting this for the benefit of others who may encounter something similar.

For working, I placed the keyboard (which is rather heavy, perhaps 100 lbs.) on the bench.

If you've had it opened before, and have in the past permanently removed the interior front panel screws as I did (those only accessible from the interior) you can skip the rather tedious first step.

BE SURE EVERY CORD - POWER, PEDAL, MIDI - is disconnected from the keyboard.

Steps:

1) Remove the top casing, for the sole purpose of accessing the interior screws to the aluminum front panel. To do this the first time, you will need to open the entire case.
a. Remove all peripherial screws from the bottom of the keyboard case.
b. Remove the screws from the back, except for the ones that hold the back panel hinges. You will need to remove the screws that hold the AC connector.
c. Gently work the panel loose with a flat screwdriver - it has a light adhesive feltlike material at the top. If you are having trouble make sure ALL the screws are out (except for the two on each hinge).
d. Once the panel is open, you will need to cut the plastic ties holding the wire bundle to the inside of the back panel, to provide enough play to remove the entire top casing of the keyboard.
e. With the fallboard shut, and a phillips screwdriver in one hand CAREFULLY begin rotating the top casing up 90 degrees along the axis congruent with the back panel. Hold the fallboard shut as you do so as gravity will want to pull it down.
f. Holding the top casing, remove the support cables restricting further movement of the top casing. You can store the screws on the speaker magnets.
g. Rotate the casing the rest of the way up. to a resting position. Ensure the steel axel of the fallboard, which will fall, does not crush any thing on the circuit board.
h. FINALLY, you can remove the interior screws holding the front panel in place. In my case, since I hope to never go through this again, I LEFT them out and bent the tabs containing the screw holes with pliers to about a 45 degree angle. You may wish to do the same, esp. for an older keyboard.

2) Remove the front panel.
a. Remove all the screws on its underside, on bottom of keyboard.

3) Remove the offending key.
a. Locate the access hole by pressing the key down. It will be under the felt visible on the keyboard, at the back.
b. Press the key down and hold it.
c. Insert a flat screwdriver, preferably one with a rough tip (lateral grooves like a file), a little ways into the hole, with the tip parallel to the front of the key (perpendicular to the sides), and pull the top of the screwdriver gently but firmly toward the front of the keyboard.
d. Continuing to apply outward force in c, and with the key still held down, use the other hand to lift the key from the front-bottom - there should be just enough space between the bottom of the depressed key and the top of the basement board to fit a finger.
e. Slowly, gently, firmly lift the key up. If you "got" and held the tab (purpose of step c), the key will suddenly pull out without a great deal of force once it reaches its normal non-depressed position. If it does not, repeat steps c-e until it does - it may require several tries, and you may need to experiment with how deeply you insert the scredriver in step c. Roland no doubt has a special tool for removing keys, but a flat screwdriver does work.
f. Once the key is free from its seating slot, the return spring will immediately push the tab loose from the key casing, making it necessary to press the adjacent key and force the tab back up. with the screwdriver coming in diagonally from the side. A combination of this, and lifting up the back wall (which bears the manufacturer's logo) should enable you to remove the key entirely, exposing the switch and the velcro-like impact strips.

In my case, I mitigated the problem by "widening" the impact strip - inserting a small piece of rubber (from a thick rubber band) between the impact strip and the bright green spongy adhesive under it. Then I applied a small piece of tape vertically to the side of the steel impact manifold extending up to top of the impact strip, to sort of hold it in place. This is a utilitarian solution, not necessarily a pretty one, but so far, so good.

Another solution I considered but did not explore would be to remove low A, and a few keys, perhaps one every fifth, work the top of the impact strip somewhat loose from its adhesive, and then, from the low A slot, pull it down a little, providing new, uncompacted strip as contact. This however, does not address compression of the underlying adhesive.

Middle C's problems are greatly mitigated - it plays like the other keys now with no detectable difference and this fix provides a satisfactory stopgap until I can afford a real piano.

I apologize for not knowing the correct terminology, but hope this description is detailed enough to help others in a similar situation in their Google/Dogpile/MSN searchquest for a solution.