Digital Piano Keyboard - Trouble shooting contact problems with Keys and Pedals

by OBZ
(Bom)

This is for a real old Digital Piano (88 keys) Roland HP-230. Here are possible solutions for trouble shooting contact problems with Digital Piano Keys and Pedals.

Living in a city with a high suspended particle matter (dust), humidity are ideal conditions for having contact problems.

I was trying to solve two kinds of problems associated with the above.

Problem 1. Extreme Bass notes (A, A#, B. C, C#, D, D#, E) are having Loud Sound and on holding the note are giving stacatto bust of Loud sound (ta ta ta tat tat)

Problem 2. Extreme Treble notes (C,B,Bb,A,Ab,G,Gb,F) are intermittently not sounding.

Problem 1
Removed the Keys and thoroughly cleaned the contacts on the PCB with IsoPropyl Alcohol and later used a Hair dryer to ensure there was no trapped moisture.

Note: Each Key Note has TWO points on the Touch Pad that make contact to the Keypad PCB. These two contact points on the Keypad are at different heights, on striking the key the higher of the two produces the sound, while the lower one suppresses the sound (something like that).

In this case, it was determined that it was the lower contact point which seemed to be the problem which attempted to be rectified by put the Carbon Dots Stickers on the Contact Points of the Touch Pad associated with the problem keys.

Also on this keyboard, I found that 12 keys were supported by one set of Touch Pads and there was 2 sets of Touch Pads on one PCB which was connected to the Main PCB via Ribbon cable (refer diagram).

Keyboard Layout
_A#___C#_D#____F#_G#_A#____C#_D#___F#_G#
A__B_C__D__E__F__G__A__B_C__D__E__F__G__A

<-----TouchPad1-----><-----TouchPad2----->
<-----------------KeyPadPCB1------------->

I swapped the Touch pad2 with the Touch Pad1 and ended up with the same problem, thus concluding that there was NO issue with the Touch Pad which is the usual culprit in most cases.

The problem was now isolated to the underlying Keypad PCB, Ribbon Cable or Main PCB



On the Keypad PCB, did doing numerous continuity test using a Lighted Continuity tester for every key (two contacts to check), also checking the Diodes, unable to find a faulty connection / ground fault

As it so happens, problem is with a Set of 8 keys, thus all 8 keys must be connected to something common that is giving this problem.

Pulled out the Ribbon Cable and put it back after cleaning both ends to ensure there were no contact problems.

I am not a qualified Electronic Tech, so I called up a qualified engineer friend and he thought it could be an IC, more so a Capacitor on the Main Board that could control this entire set of 8 keys.

So finally the only solution is to call an Experienced Tech, if anybody knows if I could be wrong in my conclusion, please post your opinion so I and others can learn and understand too.

Now Problem 2 was solved with the addition of the Carbon Dot Stickers........phew it was a busy day

I was assisting an Electrician during this operation as he has solved Contact Issues with my Piano before with my guidance.

I feel compelled to write this as I also did get help from the net in understanding few things.

One more thing, if you have a problem with a sticky Damper pedal, one will need to open the Pedal housing and identify the switches for height and how many pins. Remove the old pins with Solder Iron and solder the new Switch and you're done, this don't need a keyboard tech who will definitely charge more in comparison with a handy man / electrician.

If you only use the Sustain Pedal, then remove the switch from least used other pedals and solder it on to the Sustain Pedal and later source the replacement.

will add photos on request...

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Digital Piano Keyboard - Trouble shooting contact problems with Keys and Pedals
by: Andrea

OBZ,

Wow, I think this is one of the most comprehensive posts on this topic that I have seen. Thanks really for your efforts. I am sure you had a busy day trouble shooting the problem.

Would love to see photos if you don't mind posting them.

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