70 Silicon chip Australia’s electronics magazine siliconchip.com.au
By now I could see the whole PCB,
or at least most of it, given that some
of it was still obscured by the rubber
key switches.
The circuit board was in two halves;
one for the lower four octaves and one
for the upper four. These are stuck
(probably with similar ‘gorilla’ tape)
to the metal frame, and I really didn’t
want to have to remove them.
The fact that multiple keys up and
down the keyboard were failing meant
that the problem wasn’t localised to
one or the other circuit board, so it
must be something in common with
both causing these problems.
It didn’t take long to find a poten-
tial smoking gun. At the end of each
PCB is a multi-pin, thin-film joiner
that curls under the frame to link up
to the long flexible main-board con-
nector strips beneath.
While there is a socket mounted on
a bracket for the joiner’s silver-coat-
ed contacts to push into, on the top
the graphite or carbon pads are just
pressed onto and stuck to the corre-
sponding thin-film key PCB connec-
tions with conductive tape. This is
all held down by a clear-plastic link
pinned to the metal frame at each end
with plastic push clips.
On closer inspection, I could see
that the conductive tape had let go
in places, making contact sporadic atwithin. I couldn’t get any access at all
to the circuit board or the contacts un-
der the keys, so the only option was
to remove everything from the frame.
This was a mission in itself. Along
the top of the keyboard, flush with the
‘heads’ of the keys, were a series of
plastic locking strips. These had been
attached to the frame with very strong
double-sided tape, and I had to care-
fully pry them off one by one.
Once off, each key could be pushed
slightly forward to release the back
‘hinge’ and then maneuvered out of
the frame. With the first key, the steel
spring pinged off into the distance;
fortunately, I found it after much for-
aging under the bench. I daren’t lose
any because re-creating them would
be extremely difficult.
Getting to the heart
of the matter
The PCB was dusty underneath,
so my hopes rose that a good clean
would sort it out. I could also now see
the strips of grey rubber contact pads
that make up the top half of the key-
board switches.
These were still looking very good
and felt nice and supple; hopefully, the
carbon-composite contacts moulded
into the strips and their corresponding
printed contacts on the circuit board
below would be in a similar condition.
best. I carefully plugged the piano in
and positioned everything while the
case was open so I could power it up.
With it switched on, I could press
the rubber key contacts directly and
with the right pressure on the flex-
ible joiner connections at each end,
could get the previously non-work-
ing keys to sound. I then used a cou-
ple of small-but-strong spring-clamps
(like clothes pegs on steroids) to firm-
ly hold these contacts in place while
trying every key.
While they all worked, just tapping
on the clamps resulted in dead keys
again, so merely clamping something
stronger than the existing plastic bar
onto the connections wasn’t going to
work.Figuring out how to make
a lasting repair
There are 16 contacts each less
than 1mm wide, separated by a sim-
ilar-sized gap, on each joiner piece.
I could see most of the original con-
tact material had been stripped away
by the lifting tape. I’d need to rebuild
these contacts, and that could be a
challenge.
I had to take a break and ponder the
problem. My initial thought was to re-
place the strap with a computer IDE
ribbon cable or similar; I could solder
one end of it directly to the socket’s
PCB pads underneath, but I’d have to
work out a way to connect the other
end to the missing contacts at the thin-
film PCB end.
Then I remembered conductive
paint; I’d used this a long while ago
to good effect. Perhaps it would work
here. Maybe I could simply paint in
the missing contacts and voila!
Feeling hopeful, I ordered some
from an auction site, mainly because
it was considerably cheaper than the
paints listed on local electronics sup-
pliers’ sites.
However, when it arrived, I dis-
covered it had gone off and was use-
less. While I arranged for a refund, I
bit the bullet and shelled out $60 for
a pen-style applicator with conduc-
tive silver paint from a more reputa-
ble source.
Annoyingly, this wouldn’t work
properly either; the contents had
partially hardened. I’m still waiting
to hear back from them, but in the
meantime, I scooped a bit of the ma-
terial from inside the pen and mixed
it manually.