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GKPOWER.TXT
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2006-10-19
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149 lines
ORIGINALLY PUBLISHED IN LIMA NEWSLETTER JUNE 1988
^^^^^^^@Replacing^the^Gram^Kracker^Lithium^Battery^with^a^NiCad^Battery
^^^^^^^^^^^^^^^^^^^^^^^^^^by Mike Richardson
^^^^^^^^^^^^^^^^^^^^^^^^^Lima Ohio User Group
@NOTE: Proceed at your own risk. You assume all responsibility for decisions
to modifying a Gram Kracker. The memory chips (6264) in the Gram Kracker are
sensitive to static electricity and are easily damaged. If you are not adept
at modifying circuitry, seek help from a users group who may be able to
assist.
The average life of the lithium battery in my Gram Kracker is about 6 months.
After opening it about a half dozen times to replace the battery, the pins
between the two mother boards have become bent. I decided to install a NiCad
battery in the Gram Kracker. This article documents the procedure I followed.
@MATERIAL^REQUIRED:
.LM +5
1 Yuasa #3-51 FT-P 3.6 Vdc 50maH NiCad battery with wire leads.
1 1N4001 diode
1 10 ohm 1/4 watt resistor, SEE NOTE BELOW
.LM -5
@SOURCE^of^Battery:
.LM +5
You may order the battery from All Electronics Corp., P.O. Box 567, Van Nuys,
CA., 91408. This company has treated me fairly in the past when I was not
satisfied with an order.
Catalog # NCB-3.6PC
$1.50 each
10 for $12.50
S/H $3.00 per order
Phone # 1-800-826-5432
.LM -5
@INSTRUCTIONS:
.LM +5
1. Study the schematic and board layout before beginning.
2. Open the Gram Kracker according to the Operators Manual.
3. Momentarily place the NiCad battery behind the center switch and between the
two CMOS ram chip banks (6264). Visually inspect and confirm that the battery
will fit within your version of the Gram Kracker.
DO NOT PROCEED UNLESS YOU ARE CONVINCED THAT THE BATTERY WILL FIT!
4. Remove the lithium battery.
5. Observe the polarity markings on the lithium battery holder. Now carefully
unsolder and remove the holder. Using an ink pen, mark a small + and - sign
symbol next to the printed circuit (PC) traces that the battery holder went
through.
6. Using a pair of side cutters, gently cut the top row of leads off the center
switch (Gram 1-2 / TI BASIC). The top two leads of this switch are not
electrically connected to any circuit on the board. Now unsolder and remove
the other end of the cut switch wire leads from the board.
7. Cut one lead of the resistor to 1/2 inch length. Cut the anode lead of the
diode to 1/2 inch length. Wrap the cut lead of the resistor around the anode
lead of the diode. Solder this joint. Solder a 3 inch piece of Kynar wire
(Radio Shack wire wrap) to the cathode lead of the diode.
8. Referring to the attached sketch, install the other end of the resistor lead
in the plated thru hole and the cathode lead of the diode in the positive PC
terminal. Solder both ends on the PC board. Solder the other end of the Kynar
wire on the diode to the positive terminal of the NiCad battery.
9. Cut a 3 inch piece of Kynar wire and solder one end to the negative terminal
of the NiCad battery. Solder the other end of the wire to the PC board hole
where the old lithium battery holder was installed.
10. Put 2 small pieces of electrical tape on each end of the NiCad battery.
Press fit the NiCad battery in between the two banks of CMOS ram chips (6264).
11. Double check all your work. Check to make sure there are no solder or flux
bridges on the board. Power up the Gram Kracker at @YOUR^OWN^RISK.
12. Leave the computer on for about 20 hours to fully charge the NiCad battery.
This battery should power the battery backup circuitry for about 4 to 6 weeks
between charges.
Mike Richardson
2610 Tenth St. N.W.
Canton, Ohio 44708
.NA;NF
10 ohm
+5 >----\/\/\/\/\----|
|
|
+ | Anode
1N4001 @-----
@---
@-
@-------
| Cathode
|
----------------O
|
| /|\
| |
| |
NiCad @------- Old battery holder
Battery @--- printed circuit
@------- tracing
@--- |
| \|/
|
----------------*
|
|
@---
@|||
.LM 5;RM 75;AD;FI
Note: The +5 volts to the resistor is obtained from the plated thru hole on the
GK lower board. This plated thru hole picks up the +5 volts from the edge
connector #19 on the GK board. You will need to trace this from this edge
connector to the plated thru hole.
.NA;NF
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
| Lower Board |
| Solder Side |
---------------------------------------
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | <---bottom board,bottom side
0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 3 3 3
1 3 5 7 9 1 3 5 7 9 1 3 5 7 9 1 3 5 <---edge connector #
.LM 5;RM 75;AD;FI
Note: The "Memo Power" NiCad battery apparently has a built in current limiting
resistor. I am currently using a 10 ohm resistor in the schematic above. A
digital voltmeter reading of the voltage across the resistor indicates that the
charging current thru the NiCad is about 2ma. The old GE NiCad Battery
reference book suggest a charge rate between 0.05C and 0.1C. The 2ma rate
would be 2/50= 0.04C. Close enough! However, I leave it up to you to choose
the proper resistor value.
If anyone has some manufacture's data on these NiCads, please leave a note.
.PL 1