siliconchip.com.au Australia’s electronics magazine July 2019 71
It looked OK, so I painted it onto
two of the contacts on the joiner. It
looked the business, and after letting
it dry overnight, I tried some continu-
ity tests. It didn’t conduct at all, and
when I tried to remove it, I only suc-
ceeded in stripping more of the meagre
amount of contact material remaining
on the joiner! This effectively ruined it
and ruled out using that option again.
What to do now?
I went back to my ribbon cable idea
and found an old floppy-disk cable.
The wire spacing was identical to that
on the socket PCB, so I peeled off 16
strands, cutting off about twice the
length I’d need. I stripped 3mm of
insulation and carefully twisted and
tinned each wire. I then soldered the
wires to the socket’s PCB pads. This
was the easy part; it was the other that
caused me difficulty.
While long-time servicemen out
there are probably eye-rolling and
shouting into their magazines that I
could have used product X or Y, I set-
tled on using self-adhesive conduc-
tive copper tape to replace the half-
missing contacts on the end of the
thin-film PCB.
I cut the tape to precisely the right
size, then stuck it down with enough
left over to solder (quickly!) to the
stripped and tinned ends of the rib-
bon cable. I then clamped the plastic
link back with screws instead of pins
and tested the keyboard.
This part of the keyboard now
worked a treat, so after wrapping the
joins carefully in polymer tape, I re-
peated the process on the other side. I
cleaned everything, painstakingly re-
assembled the keyboard and got the
owner over to test it out properly. The
result was music to both of our ears!
50W laser tube replacement
This time, we had the opportunity
to be our own serviceman. The laser
tube in our laser cutter stopped lasing
(it had one job!). This is how we got it
going again...
We use our laser cutter to make cus-
tom case parts out of acrylic sheets for
some of our projects. It is one of the
“K40” types that can be purchased
from any number of online stores.
It’s a CNC machine; stepper mo-
tors move the head over the top of the
workpiece. A 50W CO 2 laser provides
the ability to cut and etch (by running
the laser at reduced power) as the head
moves around.
The cutter has a water cooling cir-
cuit to keep the laser cool, as well as
a ventilation fan to remove the plas-
tic vapours that are generated. There
is also an “air assist” system which
pushes fresh air past the lens, to keep
it from being contaminated by dust
and fumes, and to help burn away
the plastic.
The laser cutter (laser and XY ta-
ble mechanism) works quite well,
although we did initially have some
trouble with the ventilation and cool-
ing components.
We documented our fix for these
in an article in the June 2016 issue
(siliconchip.com.au/Article/9960).
Since then, the laser cutter has per-
formed well, until one day we wentto check on the progress of a cutting
job, and found that it had not only
stopped cutting, but was emitting a
high-pitched whine.
The laser is a fixed glass tube around
a metre long which is fed from a high
voltage supply; it’s kind of like a neon
tube on steroids.
The beam is reflected by three mir-
rors and focused by a lens onto a point
directly below the moving head. The
laser tubes do not have a long life
span, and the four years that this one
had been working appears to be par
for the course.
When it was powered up, there
was a corona discharge visible near
the anode, but not the usual, healthy
glow along the full length of the tube.Flowchart Coding • Vinyl Cutters • Soldering Tools • Curriculum & Resources • Filtration Systems
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