Help troubleshooting MIDI keyboard (dead keys in a row).

Thread Starter

Manolis K

Joined Feb 4, 2018
2
Hello,

I have a small MIDI keyboard (M-Audio, Axiom Pro 25) for about 10 years. I never used it much. A couple of years ago, the last 8 keys (all keys are 25 so that a good one third of it) stopped working, see attached. Other that a few violent bangs from my 3 year old while playing it, there should have been no more violent incidents in this keyboards life.

I cleaned it with cotton buds and alcohol with no success. I have read about key matrices and tried to understand how somebody would troubleshoot them with little success.

From what i've read around from people with more experience than me this probably is either a crack on the PCB or a hardware issue.

I presume that if this is a hardware thing, it is way out of my level but I would like to make sure before I quit this game. In my opinion there is no crack. I have looked on every millimeter of this PCB. I would like to be pointed at a way to make sure that buttons are doing their job sending the data necessary to the uC.

I don't know where to put my multimeter and what to expect of it.. (and why).

Any starting point help appreciated.
 

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Dodgydave

Joined Jun 22, 2012
9,637
To test the key press, put the DVM on Diode test or Low Ohms range ,ideally with "Beep on" , and follow the track of the faulty keys with the meter probes , a good track will give a Beep out , . Check the carbon tracks with the key rubber too.

The keys will be arranged in a Matrix , possibly a 5 by 5 or 6 by 5, .

Compare your readings with working keys.

The tracks will have a Common point that they use it may be broken, or the carbon tracks under the rubbers maybe cracked.
 

Alec_t

Joined Sep 17, 2013
11,730
.... or there may be a bad connection on a multi-pin plug/socket/ribbon-cable (if present) between the keys and the main pcb. Try unplugging and replugging all connectors.
 
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