How to test a used MIDI controller before buying

A used MIDI controller can look fine and still have a dead key, a loose USB port, or a knob that sends no signal. Test the controls before you pay, not after you get home.

The MIDI Test can show whether the controller sends messages when you play keys, turn knobs, move sliders, or press a pedal. Then use a quick physical check to look for wear the browser cannot detect.

Test the MIDI controller

1. Connect the controller to your computer with its USB cable and turn it on if it needs separate power. If it has a traditional MIDI OUT port instead of USB, connect it through a USB MIDI interface.
2. Open the MIDI Test in a browser other than Safari. Allow MIDI access if the browser asks, then choose the controller if the test offers a device list.
3. Play every key once, then release it. Watch the messages and check that each press and release registers. Test pads and buttons too if the controller has them.
4. Play a few keys softly and then firmly. Compare the velocity readings, which indicate how hard you played. A controller with velocity-sensitive keys should usually send different readings for soft and hard presses.
5. Turn each knob through its range, move every slider, and press and release each pedal. Check that the test receives changing messages as you move or press each control.
6. Repeat anything that seemed inconsistent. Wiggle the cable gently near the plug while playing a key, without pulling it out, to see whether the connection cuts out.

Some controllers need power from an adapter, especially when they have many pads or lights. If the device does not turn on over USB, ask the seller for the correct power supply before deciding it is faulty.

What the result means

Every key and control sends messages

The controller is communicating with the computer, and the controls you tested are producing MIDI data. This is a good sign, but it does not prove that the keys feel even, that every port works, or that the controller's audio features work. MIDI carries instructions, not sound.

One or more keys do not register

Try the same key again and check whether nearby keys work. If the same key repeatedly sends no message while the others do, its switch or internal connection may be worn or damaged. Check every key before buying, since a fault may affect only one part of the keyboard.

Keys work, but a knob or pedal sends nothing

Some controllers let you assign controls or disable them in their own configuration. A blank result does not always mean the control is broken. If the controller has settings for MIDI assignments, ask the seller to show that the control is configured, then test it again.

No messages appear

The browser may not have access to the device, the wrong device may be selected, or the cable or adapter may not carry MIDI data. Safari does not support the MIDI Test. Check the connection and permission before assuming the controller has failed.

Velocity readings barely change

The controller may be set to fixed velocity, or its velocity curve may make differences less obvious. If it has velocity settings, change the setting and test again. If the keys are supposed to be velocity-sensitive and still send nearly identical values, ask the seller whether that behavior is expected.

How to troubleshoot a failed test

1. Check power and the cable. Reseat the USB cable at both ends, try another USB port, and use the controller's power adapter if it requires one. Avoid testing through a hub until you know the controller works directly connected.
2. Allow MIDI access. Respond to the browser's MIDI permission request. If you dismissed it, use the site controls beside the address bar to review permissions, then reload the test. Use a browser other than Safari.
3. Check the selected device. If several MIDI devices are connected, choose the controller in the test's device list. Disconnect other controllers temporarily so you can identify which one is sending the messages.
4. Check whether the computer sees it. On Windows 11, right-click Start and open Device Manager, then look under Sound, video and game controllers or Universal Serial Bus controllers. On macOS, open Applications › Utilities › Audio MIDI Setup, then choose Window › Show MIDI Studio to inspect available MIDI devices.
5. Try another cable or computer. A charge-only USB cable may power a controller but carry no data. Test with a known data cable and, if possible, another computer. For a controller using traditional MIDI ports, check the interface and the connection from the controller's MIDI OUT port.
6. Review the controller's assignments. If keys work but other controls do not, check the controller's own setup for disabled controls, fixed velocity, or assignments. Restore a default setup only if the seller agrees, since it may erase their custom settings.

Check the hardware before you buy

Look closely for cracked keys, bent knobs, sticky buttons, corrosion, a loose USB socket, and damage around the power jack. Press keys across the full keyboard and compare their travel and return. A key that feels different from its neighbors can be a warning even if it still sends MIDI messages.

If the controller has MIDI IN or OUT ports, expression or sustain pedal jacks, or a separate power input, test each connection you expect to use. The browser test checks incoming MIDI messages, but it cannot confirm that the controller's MIDI OUT jack, audio output, bundled software, or every hardware feature works.

Do not buy on the assumption that a MIDI controller will make sound by itself. Many controllers only send performance data and need a computer, sound module, or other instrument to produce audio. If a key repeatedly fails, a socket cuts out, or the seller will not let you test the features you need, treat it as a repair risk and consider another unit.