Einleitung
Full teardown of a cordless phone and accessories from 2001.
Werkzeuge
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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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Use needlenose pliers to disconnect the battery connector.
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The battery is a 3.6V Nickel-Cadmium rechargeable battery made up of 3 AAA-sized cells
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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 wireless board can be flipped up, but is still attached to the main board by a short ribbon cable.
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Remove 2 screws on the main board.
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Remove 2 screws on the speaker.
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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:
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Speaker
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Message indicator LED
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Ringer switch
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Electret microphone
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Unknown potted 'Blob' IC
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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.
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The shield took about 20 minutes to remove with diagonal cutters, 2 pairs of pliers, and 3 metal spudgers.
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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:
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Toshiba TB31261AF cordless telephone RF chip
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Ceramic resonators
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Unidentified square ceramic components with 2 cylindrical holes in them horizontally (anyone who has an idea what they are, please comment.)
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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.
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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
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Phone is held together with only phillips screws.
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Battery, the most likely part to fail, is a standard component and is easily replaceable.
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Case is difficult to open.
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Wireless module is very hard to replace and impossible to repair.
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All wires (except for the battery) are soldered to the circuit board instead of using connectors.
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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.
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Remove 2 screws that hold down the main board.
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The main circuit board can be removed from the bottom case.
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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.
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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.
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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.
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This board appears to have been manufactured on April 17, 2001.
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Components on the main board:
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4 MHz crystal
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Variable capacitor
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Small audio transformer
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Miniature fuse
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Varistor for surge protection
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This board was manufactured on September 3, 2001.
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Repairability Score: 4/10
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Secondary base station is assembled with only phillips screws.
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Circuit boards use mainly through-hole parts, so repair of individual components is easier.
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Case requires lots of spudgering to open.
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Removing the board requires a long screwdriver.
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Wireless module is very hard to replace and impossible to repair.
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All wires and ribbon cables are soldered to the board and reinforced with hot glue.
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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.
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Remember how I said soldered ribbon cables were becoming a theme here? I was right.
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Remove 2 screws holding down the wireless module.
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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.
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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.
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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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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 3 screws to remove the speaker cover.
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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 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?
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Samsung K9F4008W0A-TCB0 512x8 Kb (512 KB) flash memory (designed for digital audio recording)
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Crystal oscillator, covered in the same unusual substance found on the main board.
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Unknown IC D16529CAC11CQC. Googling it turns up nothing that makes any sense.
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This board is probably where the messages are stored.
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The major components on the top case board:
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Dual 7-segment display
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LM386 audio amplifier
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Message indicator LED
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This board was manufactured on July 27, 2001.
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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
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Base station is only held together with phillips screws.
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Circuit boards use mainly through-hole parts, so repair of individual components is easier.
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Removing the top circuit board is difficult because the buttons are attached to the top case with clips.
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Opening the case requires 2 metal spudgers and a lot of force.
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Removing the bottom circuit board is difficult because the case is still attached with soldered ribbon cables.
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Wireless module is very hard to replace and impossible to repair.
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All wires and ribbon cables are soldered to the board and reinforced with hot glue.
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Overall repairability score: 5/10
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The handset battery, the most likely part to fail, is a standard component and is easily replaceable.
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Circuit boards use mainly through-hole parts, so repair of individual components is easier.
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Entire phone is held together with phillips screws
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Cases are difficult to open and require heavy spudgering.
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Most parts were not designed to be repaired.
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All wires and ribbon cables are soldered to the board and reinforced with hot glue.
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