Tuesday, October 5, 2021

Bontempi HP 544.20 keyboard repair

The HP 544.20 is a middle 80's keyboard from Bontempi (https://www.bontempi.com/).

Bontempi is an Italian musical instrument manufacturer that build low-priced instruments. This model is an electric organ that offers a Solo section with a few instruments presets and a Rhythm section.

I found this keyboard years ago on the edge of the road. It was full of ants.

First thing first I power it on, to my surprise after a couple of tries it works. So I decide to clean it.

The only problem this keyboard has is that most of the time, you have to move it, or try a few times to power it on after it works.

The keys are not so bad, they don't feels like a toy instruments. Even if the sound is not that good I decide to give a second change to this keyboard.

I've noticed that it was something on the power/amplifier board that didn't work, cause moving cables and connector on the main boards made this works.

Power stage seems good. Visual inspection seems ok. So my first try was to clean the connectors. All seems to work for a while... then after a couple of days the power on issue started again.

So I decide to scope around the board.

I've found that there's aren't problem on the audio signal coming out from the generator board to the amplifier board. So it should be something on the amplifier board.

The thing is that I've to wait for the problem to arise to check where the signal fade away. After a couple of tries I've found that the signal seems to vanish where it should not. I though it was something related to a component, but then I realize the signal is interrupted on a PCB trace.

I repeat the visual inspection, this time i focessed on the indicted PCB trace under my microscope and there i found the problem.

There's a little crack in this PCB that sometimes stops the signal. Moving PCB connectors helped cause the PCB slighlty moves and the trace conduct again.

So I simply scrape a little bit of the trace next to the crack, and solder this again.

The keyboard now is fully working.

For this reason I decided to build also a sheet music holder, that was missing. Now it's complete and ready to play.


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  • excuse my bad english