siliconchip.com.au Australia’s electronics magazine July 2019 69
-^ A keyboard without conductor
-^ 50W CO 2 laser tube
replacement
*Dave Thompson runs PC Anytime
in Christchurch, NZ.
Website: http://www.pcanytime.co.nz
Email: [email protected]
Items Covered This Month
phone fast enough, asking if I’d take a
look at this one.
I’ve been down High Expectations
Road before, so I told her all I could
do was open it up and see what was
going on. After that, we’d know the
way forward – if any. She was OK
with this and happy to pay for my
time. I also suggested that I come and
look at it first; if it was going to be an
obvious non-starter, this would save
some effort.
It turned out that she lived literally
around the corner. This KR-500 is pris-
tine, a vision in vintage dark-brown,
looking for all intents and purposes as
if she’d just had it delivered from the
shop. It didn’t have a mark on it, and
even though it had been well-played,
it showed none of the usual wear-and-
tear I usually see on older instruments.
I powered it up, and doing my best
Rachmaninov impression, tested all
88 keys one by one; I found at least a
dozen not working at all and as many
intermittent.
The period-fashionable linear pots,
LCD screen and all of the dozens of
micro-switches and tiny red LEDs on
the control panel appeared to toggle
and work properly. So did the ret-
ro, analog (but still cool-sounding)
‘rhythm’ section. So the fault lay only
with the keys.
I told her it was likely the keyboard
contacts were causing problems and
that a good internal clean might fix
things. But if that didn’t work, we’d
have limited options.
She was happy for me to assess it
further, so I arranged for her and her
husband to remove it from the stand
and bring it to my workshop in her van;
my MG isn’t the best vehicle for trans-
porting full-sized piano keyboards!
Prepping the beast for surgery
In my small workshop, the keyboardlooked even bigger. Like the majority
of Japanese-made instruments of the
era, it is incredibly well-built using
long-lasting, high-quality materials.
Splitting the case was easy; just a
matter of removing the dozen or so
standard screws holding it all together.
It was obviously made to be serviced,
with the top section hinged at the rear
corners to the internal metal chassis at
the bottom. So after releasing the vari-
ous power and ribbon cables linking
the two halves, it simply opened up
like a sandwich press.
The inside was as clean as the out-
side. These older keyboards have a lot
of PCBs stacked with rows of large,
VLSI integrated circuits. There are a
ton of components compared to mod-
ern instruments, where one or two
(likely proprietary) ICs would do the
same job.
Here, all the parts were clearly
marked and the circuit boards had
screen-printed values and part num-
bers, so if I later found that I needed a
circuit diagram, I would have no trou-
ble figuring out how it corresponded
with the actual hardware.
I made an educated guess that since
most of the keys worked, the electron-
ics were probably OK and the fault lay
with the keyboard itself. After all, it’s
the component that’s given the hard-est time by the user.
Even though the rest of the keyboard
may be pristine, over time all manner
of rubbish, sweat and other unmen-
tionables migrate down through the
gaps between the keys to foul things
up.
Most keyboards have this problem
and there isn’t a lot that can be done
about it, other than avoiding smok-
ing, drinking and perspiring while
playing. Giving the keys a good wipe-
down and a thorough hoover now and
then helps too.
This keyboard assembly was a sol-
id piece of kit. Built like the prover-
bial masonry ablutions domicile, the
backbone frame is a z-shaped piece
of folded, heavy-gauge steel securely
bolted to the substantial timber bot-
tom of the case.
Sections stamped out of the frame
accommodate and hold the spring-
steel key springs and other peripherals
while a couple of 90cm-long flexible
connectors span the length of the key-
board at the bottom, folding and split-
ting off at right-angles at the mid-point
to connect to the main PCB.
After removing the whole assem-
bly from the base and flipping it over,
I could see a green, ‘thin-film’ circuit
board peeking out from under the keys.
The problems likely lay somewhere