FT-847 Power Switch Replacement
Replacing or Fixing Broken Power Switch
There have been a number of reports of failed
power switches, so when mine got a little mechanical "hitch" in
it,
I decided to see what replacing the switch would
involve. Having looked at it all, I thought users might like
to
read about how to go about replacing the switch. Not
too hard, but not too easy, either.
First, if you're not a tinkering type of ham,
just double box the unit if the switch breaks, and send it to Yaesu
for
service. Otherwise, the tinkerer's steps follow. In
all cases, left and right refer to direction with the front of
the
radio facing you, either right side up or down. NOTE:
If you do not have experience in removing "multiple pin
with plated through holes" types of components, you might rather leave this work
to others.
The "front panel" consists of a three part
sandwich: the "black plastic facepiece," a "steel chassis," and
the
"circuit board assembly," in that order from front to
rear. The circuit board assembly holds all the rotary
controls
and switches for the rig. The rotary encoder
itself is attached to the steel chassis. First we'll remove the
black
plastic facepiece which will allow you to remove and
work on the headphone jack, if you need to. Then, we'll
remove the circuit board assembly, leaving the steel chassis still attached to
the rig. Now you can work on the
power switch.
1
Remove both top and bottom case halves by removing 8 screws (2 in handle on
right, two on left, two on front
bottom, and two on
the rear, one on top case and one on bottom. Put the case halves aside in a safe
place.
2.
Turn the
rig over onto its top with the front panel facing you. In the shuttle jog ring
is a slit you can now see.
Look in there with a
flashlight, rotate the VFO knob, and you'll see a tiny setscrew that holds the
VFO knob in
place. Use a small Allen wrench (1 mm; one
fellow reported 1.5mm fit his knob, and 1/16" fit mine one time)
and
loosen the setscrew. Slide off the VFO knob. Pull off
the shuttle jog ring. Leave the spring in there alone.
3
Remove the little black screw
immediately above the shaft for the VFO knob. It's tiny. Turn the rig back
over
so it's right side up.
4
Turn all your knobs to their
counterclockwise positions. Pull off all the knobs (but not the switch buttons!)
from
the rotary controls on the face of the rig. They just
pull off. Remove the large nuts and flat washers from the
RF
Power, Squelch, AF, and DSP controls (4 in
all).
5
You can
now remove the black plastic faceplate of the rig by lifting gently on the
molded hooks (3 on the top
and two on the bottom) that
hold the black plastic faceplate on to the steel chassis. Carefully lift the
black plastic
faceplate off the front of the radio. I had
to "work" it a little. Do it gently to make sure you have
removed
everything (it's easy to forget something) holding
the faceplate on. The buttons will stay attached to the
faceplate, and the switches themselves will stay attached to the circuit board
(which is attached to the steel
chassis). Note: the LCD
display is now no longer protected, so be careful you don't damage it. If you
have a
service manual, it might be helpful to look at the
exploded picture of the rig, but you don't need it.
6
Now, if you want, you can remove the
headphone jack by sliding the C-shaped clamp off the front of it. See
Step
8 for lowering the front panel to get the headphone
jack out the back.
7
Carefully but firmly, pull off (they
snap off and on) the switch caps from the Power and MOX switches
Howard
G6LVB reported breaking a shaft pulling the knobs
off. Remove the three large gold colored nuts and flat
washers from the remaining rotary controls (MEM/VFO, IF Shift, and
Sub-tune).
8
The
front of the rig can now be dropped down by removing two screws on the top of
each side of the case.
Loosen the two lower ones a little,
but don't remove them. You will see a slot for the lower two screws. Slide
the
whole front of the radio towards you so it can swing
down (the top of the panel comes down towards you). Make
sure the two lower screws slide to the rear of the slot or the panel won't swing
down freely. Swing the panel
down, exposing the circuit
board assembly on the back of the front panel. I usually find it handy to have
the rig
positioned near the edge of the work table so that
the dropped down part is beyond the front edge of the
table,
approximately horizontal.
9
If you are only working on the
headphone jack, you don't need to go past this step.
10
Pull all the connectors off the jacks on the back of the circuit board assembly,
except the one on the little
circuit board that's mounted
to the back of the phones jack. I jockeyed each one from the side edges until
they
came off. (As you are doing this, be sure you don't
damage the LCD panel.) Carefully cut the tie wrap that
holds
the wire bundle together on the left side of the
panel. If you do not have the voice synthesizer, you will see a
wire
assembly attached to the circuit board assembly and
just hanging in the air. You can leave this in place
regardless.
11
Remove the three gold colored Phillips-head screws on the circuit board assembly
on the back of the steel
chassis. DO NOT straighten any of
the bent metal tabs that hold the LCD display into the circuit board;
leave
them alone.
12
The Power and MOX switches are still
not exposed. Carefully lift the whole circuit board assembly from
the
back of the steel chassis. I had to "work" this, too.
Keep in mind that all the rotary knob shafts are attached
to
the circuit board assembly and need to come out
relatively straight. There are tabs on the steel chassis that
help
hold the circuit board assembly in place; just ease
those out of the way so the circuit board assembly can slide
off
the steel chassis. The encoder will stay in place on
the steel chassis. NOTE: You may find that you will need
to
remove the lower screws to free up the front panel.
It's a bit of a three-hand affair, and there are some
cables
that will stay attached between the panel and the
radio.
13
Now the
Power and MOX switches are exposed, and you can unsolder and remove it or them.
The switches
seem to fail in two ways: contact burns and
mechanical failure of the latch. Gary N5IXI (his were burned) said
he
simply flipped the power switch (or the internal piece)
over and used the spare set of pins. I guess it will
depend
on how your switch fails. I suggest getting a new
switch instead. They only cost $1.88 from Yaesu.
14
Unsoldering the switch requires
proper equipment and attention to detail. Some sort of desoldering
equipment
is needed, say solder wick and/or a heated
solder sucker. Be careful not to melt the jack next to the switch
and
not to lift the traces. Although the holes are plated
through, there are no contacts on the hidden side, only on
the
side you will unsolder from. If you have never removed
components such as the switch, this is probably not the
best place to learn (although some would have it no other way). Be careful of
your LCD screen when you're
working on the back side of
the circuit board.
15
Reassembly is the opposite of
removal. But, before reassembling, read below the table for some
suggestions
for things to do while you've got everything
apart.
16
Put the
circuit board assembly back in from the rear, making sure you don't pinch the
wires going to the left
side of the board or the encoder
wires in the bottom center of the board. Pop the board into place, making
sure
the switches are all going through the holes (in the
steel chassis) intended for them. Install the three screws
that
hold the circuit board assembly to the steel chassis.
Reinstall three large flat washers and the gold colored
nuts
on the MEM/VFO, IF Shift, and Sub-tune knobs. Tighten
the nuts.
17
Flip
up the front panel and secure it with the four edge screws. Make sure you push
the bottom of the front
panel in all the way before
tightening the four screws. Snap the caps back on the Power and MOX switches
and
check that the switch action is
OK.
18
Carefully
slide the black plastic facepiece into place, so the molded parts snap into
place on the edge of the
steel chassis. Check the
switch action for all the knobs to make sure they're engaged with the switches
on the
circuit board assembly. Be especially mindful that
the Clarifier and the Tune switch caps don't get
dislodged.
19
Reinstall the little black screw that goes above the VFO shaft. Slide the
shuttle jog ring back on. Put your Allen
wrench in the
screw for the main VFO knob, then slide the knob and Allen wrench on the shaft
and tighten down
the VFO knob.
20
Reinstall the flat washers and silver
colored nuts on the rest of the rotary switches (RF Power, Squelch,
AF,
and DSP). Push all the knobs back on. The "ring" type
knobs that go on two knob controls can be put on many
different ways, so make sure you get the white lines where you want them.
Reinstall the outside covers for the
rig (bottom has to go
on first) and secure with the eight screws.
While you've got the radio apart, now is a
good time to do some other housekeeping. First, you can slide off
the
metal clip that holds the headphone jack in place, and
remove the jack and the circuit board attached to it. It
comes out to the rear. This makes it very easy to change the resistors for
headphone balancing. I had changed
my resistors with
everything installed, so I just inspected my work, now that I could easily see
it. You can work
on the headphone assembly after you have
removed only the black plastic facepiece.
The other thing to do, if your rig is a year or
more old, is to clean out the collection of dirt, lint, cat and dog
hair,
etc., that the fans have faithfully sucked into the
rig. One way to do this is to remove the large metal panel
that
covers the circuitry on the top of the rig. Remove 12
screws and lift the cover off. On the left is the V/U
power
amp board. Mine was dusty and covered with junk. You
can also now see both the fans to clean them. The PA
board
for HF is another layer down; I did not take any boards out to view that board,
but it is probably a good
idea to do it. (And report how
to the bulletin board!)
It's also a good time to do a mod to the rear
fan to quiet it down. I just soldered three diodes in line with
the
positive lead to drop the voltage a little. Others
have put in resistors. Still others have simply unplugged the
rear
fan. Consider your cooling needs first,
though.