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