Olympus
BH
‐
2
(BHT/BHTU)
Electronics
Revision
2
Page
6
of
24
extinguishing
the
6V
LED.
If
the
setting
of
the
intensity
control
is
decreased
to
the
point
where
the
clamped
control
signal
exceeds
the
threshold
waveform,
the
6V
LED
will
completely
extinguish.
The
operation
of
the
remaining
three
comparators
is
similar
to
this
one,
differing
only
in
their
threshold
voltages.
Power
LED
Resistor
R203
and
LED
“A”
function
as
the
power
‐
on
indicator
for
the
microscope.
Errors
in
the
Olympus
Documentation
In
the
course
of
researching
this
document,
two
errors
were
identified
in
the
schematic
diagram
published
in
the
Olympus
Research
Microscope
Series
BH2
(BHS)
Repair
Manual
.
Both
of
these
errors
are
in
the
LED
bar
‐
graph
display
circuitry.
Bar
‐
Graph
LEDs
The
first
error
is
in
the
wiring
of
the
four
bar
‐
graph
LEDs,
as
shown
in
Detail
1
of
Appendix
2
and
Appendix
3
of
this
document.
The
Olympus
manual
shows
these
LEDs
wired
with
their
cathodes
connecting
to
their
respective
comparator
outputs
and
with
their
anodes
wired
to
their
respective
current
‐
limiting
resistors.
The
actual
circuit
configuration
(as
observed
on
the
main
boards
of
functional
BHTU
equipment)
has
the
anodes
of
the
four
LEDs
connected
to
the
filtered
DC
power
supply
line
and
the
cathodes
connected
to
their
respective
current
‐
limiting
resistors.
This
is
a
minor
discrepancy
and
either
configuration
would
work
equally
well,
but
the
actual
as
‐
built
configuration
is
shown
in
this
document.
Control
‐
Signal
Clamping
Network
The
second
error
is
in
the
wiring
of
the
control
‐
signal
clamping
network,
as
shown
in
Detail
2
of
Appendix
2
and
Appendix
3
of
this
document.
The
Olympus
manual
shows
this
network
fed
from
the
full
‐
wave
‐
rectified
output
of
the
bridge
rectifier,
but
in
the
actual
circuit
configuration
(as
observed
on
the
main
boards
of
functional
BHTU
equipment),
this
network
is
fed
from
the
filtered
DC
power
supply
line.
This
error
is
of
greater
consequence
than
the
first,
as
the
circuit
published
in
the
Olympus
repair
manual
would
not
guarantee
that
the
LEDs
remain
off
around
the
zero
crossings
of
the
AC
line.
Removing
the
Electrical
Base
from
the
Stand
To
gain
access
to
the
electronics
in
the
base
of
the
BHT/BHTU
stand,
the
electrical
base
must
be
removed
from
the
base
of
the
stand.
Be
sure
to
take
sufficient
notes
and
plenty
of
photographs
both
before
and
during
the
disassembly
process
to
make
sure
that
everything
can
be
correctly
reassembled
later
on.
Before
removing
the
electrical
base,
look
at
the
right
‐
hand
side
of
the
unit,
just
above
the
intensity
slider,
and
note
whether
or
not
a
light
preset
control
and
switch
are
present.
The
earlier
units
did
not
include
these
components,
but
the
later
ones
did.
Next,
remove
all
the
major
components
from
the
microscope
stand
(i.e.,
AC
power
cord,
condenser,
stage,
eyepieces,
viewing
head,
and
objectives).
Doing
so
will
make
the
stand
easier
to
maneuver
and
will
prevent
inadvertent
damage
to
these
components
during
disassembly
and
reassembly.
Be
sure
to
protect
these
components
from
dust
and
damage
while
they
are
not
installed
on
the
stand.
After
removing
these
components,
cover
the
top
of
the
arm
(i.e.,
the
nosepiece
turret
and
the
exposed
mounting
dovetail
for
the
viewing
head)
with
a
clean
plastic
bag
and
secure
this
with
a
rubber
band
to
keep
dust
out
of
these
openings.
This
is
especially
important
on
BHTU
stands
which
have
an
optical
correction
lens
located
just
below
the
viewing
head
to
correct
for
the
difference
in
tube
length
introduced
with
the
reversed
nosepiece.
With
the
stand
in
its
normal
upright
position,
remove
the
lamp
house
from
the
back
of
the
base.
The
lamp
house
simply
plugs
into
the
base,
and
can
be
removed
by
grasping
it
and
pulling
it
straight
back.
Set
the
lamp
house
aside
to
prevent
damage.
Do
not
touch
the
halogen
lamp
with
your
fingers,
as
oils
from
your
skin
will
cause
premature
failure
of
the
bulb.
If
the
bulb
is
accidentally
touched,
clean
it
with
isopropyl
alcohol.
Carefully
turn
the
stand
upside
down,
exercising
caution
to
prevent
impacts
to
the
focus
knobs
and
to
the
condenser/stage
holder.
Using
a
5/32”
Allen
tool,
remove
the
four
hex
socket
‐
head
cap
screws
from
the
bottom
of
the
