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.

Image 1/3: Image 2/3: Image 3/3:
  • 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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Image 1/3: Remove the battery door on the back. Image 2/3: Remove the battery door on the back. Image 3/3: Remove the battery door on the back.
  • Part I: The Handset.

  • Remove the battery door on the back.

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Image 1/3: The battery is a 3.6V Nickel-Cadmium rechargeable battery made up of 3 AAA-sized cells Image 2/3: The battery is a 3.6V Nickel-Cadmium rechargeable battery made up of 3 AAA-sized cells Image 3/3: The battery is a 3.6V Nickel-Cadmium rechargeable battery made up of 3 AAA-sized cells
  • 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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Image 1/1:
  • Remove 2 phillips screws inside the battery compartment.

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Image 1/3: Image 2/3: Image 3/3:
  • After some aggressive spudgering (the pictures make it look much easier), the back of the case can be removed.

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Image 1/1:
  • The charging contacts can now be easily removed.

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Image 1/2: Image 2/2:
  • Remove 2 screws on what appears to be the wireless board.

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Image 1/3: Remove 2 screws on the main board. Image 2/3: Remove 2 screws on the speaker. Image 3/3: Remove 2 screws on the speaker.
  • 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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Image 1/2: Image 2/2:
  • The mainboard assembly can now be removed from the front case.

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Image 1/2: Image 2/2:
  • 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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Image 1/2: Speaker Image 2/2: Message indicator LED
  • 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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Image 1/3: The shield took about 20 minutes to remove with diagonal cutters, 2 pairs of pliers, and 3 metal spudgers. Image 2/3: Needless to say, the shield is irreversibly damaged and the wireless module will probably never work again. Image 3/3: Needless to say, the shield is irreversibly damaged and the wireless module will probably never work again.
  • 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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Image 1/2: Toshiba [http://pdf.datasheetcatalog.com/datasheets2/27/2716702_1.pdf|TB31261AF] cordless telephone RF chip Image 2/2: Ceramic resonators
  • 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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Image 1/2: Phone is held together with only phillips screws. Image 2/2: Battery, the most likely part to fail, is a standard component and is easily replaceable.
  • 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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Image 1/2: Remove 2 phillips screws on the bottom. Image 2/2: Remove 2 phillips screws on the bottom.
  • Part II: The Secondary Base Station

  • Remove 2 phillips screws on the bottom.

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Image 1/3: Image 2/3: Image 3/3:
  • The top case can be removed with some spudgering.

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Image 1/3: Image 2/3: Image 3/3:
  • Remove 1 screw to remove the wireless module.

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Image 1/3: Remove 2 screws that hold down the main board. Image 2/3: Remove 2 screws that hold down the main board. Image 3/3: Remove 2 screws that hold down the main board.
  • 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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Image 1/3: Remove 4 screws holding in the button board and charging contacts from the top case. Image 2/3: Remove 4 screws holding in the button board and charging contacts from the top case. Image 3/3: Remove 4 screws holding in the button board and charging contacts from the top case.
  • 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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Image 1/3: 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. Image 2/3: 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. Image 3/3: 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.
  • 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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Image 1/2: The plastic pieces used to hold down the board can also be removed. Image 2/2: The plastic pieces used to hold down the board can also be removed.
  • 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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Image 1/1: This board appears to have been manufactured on April 17, 2001.
  • 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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Image 1/2: 4 MHz crystal Image 2/2: [https://en.wikipedia.org/wiki/Reed_relay|Reed relay]
  • 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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Image 1/2: Secondary base station is assembled with only phillips screws. Image 2/2: Circuit boards use mainly through-hole parts, so repair of individual components is easier.
  • 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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Image 1/3: First step: remove 4 screws. Image 2/3: First step: remove 4 screws. Image 3/3: First step: remove 4 screws.
  • Part III: The Main Base Station

  • First step: remove 4 screws.

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Image 1/3: Remember how I said soldered ribbon cables were becoming a theme here? I was right. Image 2/3: Remember how I said soldered ribbon cables were becoming a theme here? I was right. Image 3/3: Remember how I said soldered ribbon cables were becoming a theme here? I was right.
  • 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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Image 1/2: Image 2/2:
  • Remove the buttons from the side of the case.

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Image 1/3: Remove 2 more screws holding down the plastic pieces attached to the circuit board. Image 2/3: Remove 2 more screws holding down the plastic pieces attached to the circuit board. Image 3/3: Remove 2 more screws holding down the plastic pieces attached to the circuit board.
  • 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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Image 1/2: Remove the microphone from its holder. Image 2/2: Remove the microphone from its holder.
  • Remove another 2 screws on the other side of the board.

  • Remove the microphone from its holder.

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Image 1/3: All of the cables to the main board can now be cut and the wireless module can be cut off of the main board. Image 2/3: All of the cables to the main board can now be cut and the wireless module can be cut off of the main board. Image 3/3: All of the cables to the main board can now be cut and the wireless module can be cut off of the main board.
  • 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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Image 1/2: [http://www.ti.com/lit/ds/symlink/lm124-n.pdf|LM324] Quad Operational Amplifier Image 2/2: Electret microphone
  • 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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Image 1/2: Image 2/2:
  • 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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Image 1/2: Image 2/2:
  • Remove 2 screws to remove the charging contacts in the upper case.

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Image 1/3: 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. Image 2/3: 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. Image 3/3: 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.
  • 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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Image 1/2: Image 2/2:
  • The upper case board can be removed by removing 5 screws.

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Image 1/2: Image 2/2:
  • Remove 4 screws on the mysterious metal box.

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Image 1/2: Image 2/2:
  • 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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Image 1/3: [http://www.prom-electric.ru/data/uploads/datasheets/Samsung%20Electronics%20Co/NAND%20Flash/k9f4008w0a.pdf|Samsung K9F4008W0A-TCB0] 512x8 Kb (512 KB) flash memory (designed for digital audio recording) Image 2/3: Crystal oscillator, covered in the same unusual substance found on the main board. Image 3/3: Unknown IC [https://www.google.com/search?q=d16529cac11cqc&biw=1280&bih=688&source=lnms&sa=X&ved=0CAYQ_AUoAGoVChMIo7624NapxwIVTReSCh1g8QEY&dpr=1|D16529CAC11CQC]. Googling it turns up nothing that makes any sense.
  • 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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Image 1/3: Dual 7-segment display Image 2/3: [http://www.ti.com/lit/ds/symlink/lm386.pdf|LM386] audio amplifier Image 3/3: Message indicator LED
  • 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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Image 1/2: Image 2/2:
  • 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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Image 1/1: Base station is only held together with phillips screws.
  • 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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Image 1/1: The handset battery, the most likely part to fail, is a standard component and is easily replaceable.
  • 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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