Introduction

Full teardown of a cordless phone and accessories from 2001.

This teardown is not a repair guide. To repair your GE 27990G3 Cordless Phone, use our service manual.

  1. This is a teardown of a GE 27990G3 cordless phone system from 2001. Sadly, while it still works, its 2.4 GHz wireless transmitter interferes with WiFi.
    • This is a teardown of a GE 27990G3 cordless phone system from 2001. Sadly, while it still works, its 2.4 GHz wireless transmitter interferes with WiFi.

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  2. Part I: The Handset.
    • Part I: The Handset.

    • Remove the battery door on the back.

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    • Use needlenose pliers to disconnect the battery connector.

    • The battery is a 3.6V Nickel-Cadmium rechargeable battery made up of 3 AAA-sized cells

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    • Remove 2 phillips screws inside the battery compartment.

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    • After some aggressive spudgering (the pictures make it look much easier), the back of the case can be removed.

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    • The charging contacts can now be easily removed.

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    • Remove 2 screws on what appears to be the wireless board.

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    • The wireless board can be flipped up, but is still attached to the main board by a short ribbon cable.

    • Remove 2 screws on the main board.

    • Remove 2 screws on the speaker.

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    • The mainboard assembly can now be removed from the front case.

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    • The wireless board is attached by a soldered and hot-glued in ribbon cable, which must be cut off to remove.

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    • Components on the main board:

      • Speaker

      • Message indicator LED

      • Ringer switch

      • Electret microphone

      • Unknown potted 'Blob' IC

      • Piezo buzzer for ringer

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    • Whoever designed the wireless module really didn't want anyone to know what was inside. The very thick EMI shield is soldered, crimped, and epoxied on.

    • The shield took about 20 minutes to remove with diagonal cutters, 2 pairs of pliers, and 3 metal spudgers.

    • Needless to say, the shield is irreversibly damaged and the wireless module will probably never work again.

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    • Components inside the wireless module:

      • Toshiba TB31261AF cordless telephone RF chip

      • Ceramic resonators

      • Unidentified square ceramic components with 2 cylindrical holes in them horizontally (anyone who has an idea what they are, please comment.)

    • The back of the board says that it was manufactured on August 29, 2001, making the phone 14 years old at the time of writing.

    • Interestingly, the Toshiba TB31261AF is designed for a 900MHz cordless telephone, but this is a 2.4GHz model.

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    • Repairability score: 6/10

    • Phone is held together with only phillips screws.

    • Battery, the most likely part to fail, is a standard component and is easily replaceable.

    • Case is difficult to open.

    • Wireless module is very hard to replace and impossible to repair.

    • All wires (except for the battery) are soldered to the circuit board instead of using connectors.

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    • Part II: The Secondary Base Station

    • Remove 2 phillips screws on the bottom.

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    • The top case can be removed with some spudgering.

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    • Remove 1 screw to remove the wireless module.

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    • Just like in the handset, the wireless module is connected to the main board with a soldered ribbon cable. I'm sensing a theme here.

    • Remove 2 screws that hold down the main board.

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    • The main circuit board can be removed from the bottom case.

    • Remove 4 screws holding in the button board and charging contacts from the top case.

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    • The wireless module can be cut away from the logic board.

    • This wireless module is identical to the one in the handset except for the fact that it used coiled wires instead of straight wires for antennas.

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    • Remove 2 screws to remove the support for the wireless module.

    • The plastic pieces used to hold down the board can also be removed.

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    • The button board contains a lonely button, 2 LEDs, and is connected with a soldered ribbon cable reinforced with hot glue.

    • This board appears to have been manufactured on April 17, 2001.

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    • Components on the main board:

      • 4 MHz crystal

      • Reed relay

      • Variable capacitor

      • Small audio transformer

      • Miniature fuse

      • Varistor for surge protection

    • This board was manufactured on September 3, 2001.

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    • Repairability Score: 4/10

      • Secondary base station is assembled with only phillips screws.

      • Circuit boards use mainly through-hole parts, so repair of individual components is easier.

      • Case requires lots of spudgering to open.

      • Removing the board requires a long screwdriver.

      • Wireless module is very hard to replace and impossible to repair.

      • All wires and ribbon cables are soldered to the board and reinforced with hot glue.

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    • Part III: The Main Base Station

    • First step: remove 4 screws.

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    • The case for the main base station can be opened, but it requires 2 spudgers and much more force than the other one.

    • Remember how I said soldered ribbon cables were becoming a theme here? I was right.

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    • Remove the buttons from the side of the case.

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    • Remove 2 screws holding down the wireless module.

    • Remove 2 more screws holding down the plastic pieces attached to the circuit board.

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    • Remove another 2 screws on the other side of the board.

    • Remove the microphone from its holder.

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    • In order to remove the board from the bottom case, you have to carefully reach in and free each one of the plastic pieces attached to the board from a clip on the bottom case.

    • All of the cables to the main board can now be cut and the wireless module can be cut off of the main board.

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    • Components on the main board:

      • LM324 Quad Operational Amplifier

      • Electret microphone

      • Small audio transformer

      • Reed relay

      • Same potted 'Blob' IC found in the handset

      • HEF4053 triple SPDT analog switch

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    • The main board in the base station has patches of an unknown yellowish-brown substance on it that appears to be some kind of weak adhesive, and it seems to be scattered in no obvious pattern.

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    • Remove 2 screws to remove the charging contacts in the upper case.

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    • Remove 3 screws to remove the speaker cover.

    • This speaker cover appears to have been designed to accomodate both a low-profile speaker and a speaker with a larger magnet on the back.

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    • The upper case board can be removed by removing 5 screws.

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    • Remove 4 screws on the mysterious metal box.

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    • The entire top case assembly can be removed from the printer after using a spudger to free the large buttons from clips in the top case.

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    • So what is inside the mysterious metal box?

      • Samsung K9F4008W0A-TCB0 512x8 Kb (512 KB) flash memory (designed for digital audio recording)

      • Crystal oscillator, covered in the same unusual substance found on the main board.

      • Unknown IC D16529CAC11CQC. Googling it turns up nothing that makes any sense.

      • This board is probably where the messages are stored.

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    • The major components on the top case board:

      • Dual 7-segment display

      • LM386 audio amplifier

      • Message indicator LED

    • This board was manufactured on July 27, 2001.

    • The speaker is a standard 2" low profile 8 ohm 0.25 watt speaker.

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    • All of the boards in this phone system have terrible solder quality. I was able to cleanly remove the 7-segment display, about 20 capacitors, 3 voltage regulators, 1 transformer, and 2 crystal oscillators without damaging them using needle nose pliers.

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    • Repairability Score: 3/10

    • Base station is only held together with phillips screws.

    • Circuit boards use mainly through-hole parts, so repair of individual components is easier.

    • Removing the top circuit board is difficult because the buttons are attached to the top case with clips.

    • Opening the case requires 2 metal spudgers and a lot of force.

    • Removing the bottom circuit board is difficult because the case is still attached with soldered ribbon cables.

    • Wireless module is very hard to replace and impossible to repair.

    • All wires and ribbon cables are soldered to the board and reinforced with hot glue.

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    • Overall repairability score: 5/10

    • The handset battery, the most likely part to fail, is a standard component and is easily replaceable.

    • Circuit boards use mainly through-hole parts, so repair of individual components is easier.

    • Entire phone is held together with phillips screws

    • Cases are difficult to open and require heavy spudgering.

    • Most parts were not designed to be repaired.

    • All wires and ribbon cables are soldered to the board and reinforced with hot glue.

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Attached Documents

jrw01

Member since: 08/22/2013

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