On 11/18/2014, 6:30 PM, Arfa Daily wrote:
I avoid keyboards whenever I can. They are heavy, have too many screws
in, and take up too much bench space. On this occasion however, I was
asked to look at a Korg LP-350 electric piano by a music store that I
have only recently started doing work for, so had to be 'accommodating'
to ...

The shop owner said it was dead, and that he had tried another power
supply already. I figured that this might be something nice and
straightforward like a socket busted out of the board. When it arrived,
I was delighted to see that the socket and on - off switch were located
in a largish 'pod' secured to the bottom of the unit with just 6 screws.
So I stood the unit vertically, leaned against the bench, and removed
the pod. In fact, the entire electronics seems to be on a single board
in this enclosure, with just the keyboard itself and the control
switchery being in the main part of the cabinet. The problem turned out
to be some miniscule little sm device in series with the DC connector
centre pin. It is too small to have any value marked on it, but does
have the designation "R" on the board so maybe its a tiny safety
resistor (anyone know ?)

So to get it going initially and check for any other problems, I hung a
1 ohm fusible R across the pads. This restored life to the LEDs on the
control section, so I hooked it to an amp. And this is where it got odd
- for me at least.

Some notes sort of worked, although you had to pound them quite hard.
Other notes didn't work at all. Then when you went back to one that
worked a few seconds ago, now it didn't. Clearly, it's a keyboard with
full velocity sensing, but this seemed very arbitrary as well. My heart
was just beginning to sink when I decided to turn it 'right way up' i.e.
horizontal, just in case. And Lo! Then it all worked. Every note was
fine, and the 'touch' behaved perfectly. Now I don't pretend to
understand keyboards, but as far as I can recall, all the ones that I've
previously seen have either been based on bus bars and springy contacts,
or rubber keymats.

So how is this one done such that it won't work when the unit is
standing upright on its end ?

Arfa

Mercury switches?

John :-#)#

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