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Replacing the Memory Backup Battery in
a Harris RF-590 Receiver
I recently acquired a Harris RF-590 receiver with a memory
backup battery of unknown age, but still holding a charge. Rather than wait for
the battery to fail, and risk damaging the printed circuit board, I decided to
replace it with a new battery.
As shipped from Harris, a 3.6V NiCd rechargeable battery
is installed on the main control board to back up channel memory, allowing the
receiver to retain channel settings when the power is removed. When a NiCd
battery leaks, a corrosive fluid flows that will destroy printed circuit
board traces. My Updates entry for 12 July 2007 shows the results of a leaky
NiCd battery in an HP 8116A function generator.
http://www.cliftonlaboratories.com/july_2007.htm. In that case, damage to
the PCB was minimal.
Rather than replace the battery with another NiCd, I
decided to use a NiMH battery which should last longer and should be less prone
to leakage. Mouser stocks a pin-identical NiMH battery, Part No. 672-55615703
which costs $10.18.
Tools required:
- Philips screwdrivers, No. 1 and No. 2 size.
- Large flat blade screwdriver.
- Soldering iron, solder and solder wick. I also used a
vacuum desoldering tool.
Replacing the battery took me about 45 minutes.
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Procedure
You will need a clear workbench area large enough to hold the receiver.
Removing the battery pack will clear the channel memories,
so if their contents are important to you write the values down and re-enter the
data when the replacement is completed.
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Step 1
Remove the power cord and any attached cables. Remove the front and bottom
chassis covers with the flat blade screwdriver. Both covers are held in place
with quarter-turn Dzus fasteners.
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Step 2
Loosen the four front panel retaining screws. Use a No. 2 Philips screwdriver.
These are captive screws and should be loosened until they are free to move back
and forth. The illustration below shows the screws partially obstructed by the
rack handle. That was not the case on my receiver.
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Removing the four retaining screws allows the front panel to hinge forward, 90
degrees, flat on the workbench.You should be able
to see the controller board and backup battery. The battery is in the lower left
corner of the controller board. (I do not know if this is the case for all
revisions of the controller board.)
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My receiver has a 1989 manufacture date, and the battery (Panasonic) has a date
code I take to be 1994, some 16 years ago. I assume this means the battery was
replaced at least once. It also means that the replacement battery has lasted 16
years and still holds a charge, which is amazing. That's much longer than I've
found in other equipment
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Step 3
The controller board is held in place with eight captive screws. Access to the
bottom four screws is not possible with the front panel in place, so it is
necessary to remove the two hinge screws securing the front panel to the main
chassis.
The photo below shows the left side hinge screw--the arrow
points at screw head - reachable via a recess in the vertical bracket. The screw
threads are visible just below the connector, and are centered in the red
circle.
Remove the hinge screws from the left and right side. This
detaches the front panel from the chassis. The cables are long enough to allow
the front panel to move a couple of inches, which is all that is required.
You may find the next step easier to implement if you
raise the receiver chassis a couple inches above the workbench or allow the
front panel to overhang the bench's front edge. If so, hold the front panel
in place to avoid stressing the connecting cables.
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Step 4
Remove all the controller board plug in cables. Most will have a "pull loop"
attached to make the job easier. Note that cables attach from both the top and
bottom of the board.
The cables are keyed to make it difficult to replace them
improperly, but you may wish to make a note of which cable is associated with
which jack.
Loosen the eight captive screws holding the controller
board to the vertical panel assembly and carefully remove the controller board.
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Step 5
Remove the old battery pack. The battery pack has four pins, two of which are
internally unconnected but are used to mechanically hold the battery pack to the
PCB, as well as plus and minus pins.Use your
favorite technique to unsoldering the battery. I started with solder wick, and
then used a vacuum desoldering tool, while applying slight pressure to the
battery pack with a small screwdriver between the PCB and battery pack bottom
surface.
When the old battery pack is removed, clean the four
mounting holes of any residual solder. Write the installation date on the new
battery pack.
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Step 6
Install the new battery pack. The pin spacing is such that it can only be
installed in the correct orientation.
Because I had difficulty removing the old battery pack, I
decided to only solder the positive and negative pins, and leave the two
unconnected pins unsoldered. This will make it easier to replace the battery
next time, but reduces the mechanical soundness of the mounting, an acceptable
exchange in my view.
After the battery pack is soldered in place, clip the four
pins flush with the board.
The photo below shows the controller board with the new
battery pack installed. |
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Step 7
Reinstall the controller board and tighten the eight captive screws. When
reinstalling the controller board, be careful not to trap connectors between the
board and the shield the board mounts against. Also be careful not to stress the
front panel cables.Reattach all connectors to the
controller board.
Reinstall the two hinge screws
Swing the front panel back to its normal position and
tighten the four captive retaining screws.
Replace the top and bottom covers.
Reconnect the power cord and any attached cables.
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This should complete your battery replacement. To charge the
new battery, leave the receiver on for several hours.
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