One key sounds louder than the others

This will be a problem with the key contact sending the wrong velocitiy. To verify, hook it up to a midi source and see if the same thing happens in the connected device. If so, it will need to go into the shop for repair.

I am not an expert but with the little knowledge I have I would suggest the following.
Check the 'Throw' on the hammer, is throwing the same distance as all the other hammers.
Check the felt dampening, this usually moves when you press one of the pedals. Is the felt different to the other keys.
A lot also depends on which string it is, top end or bass. The string could be past it's sell by date and causing the problem.
Hope this helps in some small way.
Regards

Maybe try adjusting the MASTER level?

Good Luck

Other settings
Adjusting the master level You can adjust the level of the headphone and the stereo out by turning the MAIN VOLUME knob. The MAIN
VOLUME changes the analog signal level. This will also adjust the entire level of the MPC1000 digitally.
01. Press the [MODE] key and then the [PAD 10] (OTHER).
It switches to the OTHER mode.
02. Press the [F1] (GLOBAL) key.
The GLOBAL page will be displayed.
03. In the Master level field, set the level.
You will set the digital signal level, which will be sent out to the DA converter. The MPC1000 can output up to
32 sounds simultaneously. There is the great difference in the level when you play single sample and play 32
sounds. If you increase the value in the Mater level field, you can increase the entire level of the MPC1000 to
create more powerful sound with less noise. However, if you playback many sounds at the same time, the
level may be overloaded, which may cause distortion. If you decrease the value in the Master level field, you
can prevent distortion when you play many sounds at the same time. However, you cannot have a good
result in respect to the noise or punch of the sound. Set the appropriate value in the Master level field
depending on the application.

hi Peter
try to change to organ sound if is not happened the problem is the rubber contact under the keyboard (clean o change the rubber)

Hi Peter
open the instrumet and change the rubber contact

EP-50's are notorious for problems with either the 4.65 voltage feed to the velocity sensitive keys or failure of the small zenner diaodes. Each key has a pair fo split circles on the circuit board under it. When you hit the key you connect each side of the circles and the harder you hit the keys the quicker the circuits close the louder the sound. Problem is if the voltage to either circle fails, due to bad solder, scratch on circuit board, failed diaode then the sound disappears. The fix is simple if you are knowledgeable on solder on circuit boards, can use a multimeter and can dissassemble and reassemble the keyboard. If you have to take it to a repair shop it is probably not worth fixing as this is not one of the better Roland products

Hi,
I’m repairing a casio cdp-220r for the same reason. The F3 key does not sound at all and some adjacent keys sound louder than the rest at normal play attack. I will have to replace the entire octave memebrane as I found that it was broken when I finally got access to it. See phot

Each key has two contacts which close at different times as a key is pressed which is how key velocity is measured. The failing key has one contact that isn't making resulting in the velocity is measured at max velocity so it is LOUD.

You need to clean the contacts which are usually conductive rubber pills pressed against circuit traces on a circuit board under the keys. The contacts should be cleaned using 99% isoprophyl alcohol and Q Tips.

What has happened is that one of the contacts on those notes is not working properly. Each key has two contacts. One makes before the other as the key is pressed. The processor MEASURES the time between those as you hit the key to read the VELOCITY you have hit the key with. This velocity is often used for loudness on many voices such as the piano. These contacts are USUALLY conductive rubber pills suspended in silicone rubber "domes". One can disassemble the key area and clean BOTH the black rubber pills and the circuit traces they are pressed against using Q Tips and ONLY 99% isoprophyl alcohol to restore proper operation
One needs to be very careful when disassembling unit as there are many tender ribbon cables and connectors. Best to have clear work area and two people to "control" the halves of the shell while opening..

If it has a sequencer/ recorder built in, you have the ability to change the pitch/ detune by using some key strokes after initiating the program mode. If your not sure how to do that, try unplugging the keyboard for thirty seconds and push the power button while it's unplugged, then plug it back in. Any better? What model is it.