landline – Experimental Engineering

Another random teardown from the junk box time!
Here’s an old Motorola DECT landline phone, no use to me as I’ve not used a landline for many years.

Not much on the back, other than the battery compartment for a pair of AAA rechargables. The base unit contains the charger.

Here’s the main PCB removed from it’s casing. There’s not really much going on, one of the main ICs, which is probably a microcontroller, is a COB device, so no part numbers from there. There’s a row of pads for programming the device at the factory. The RF section is on a dedicated IC, a DE19RF19ZCNC from DSP Group. I couldn’t find much on this part, but it’s one of a range of DECT/VoIP DSP devices.

Inside the base unit is a similar board, just without the keypad. Main microcontroller is again a COB device, the RF IC is under the shield.

Removing the shield reveals the same IC as in the handset, only this PCB has a pair of antennas.

This is an old cordless landline phone, with dead handset batteries.

Here’s the handset with the back removed. Shown is the radio TX/RX board, underneath is the keyboard PCB with the speaker & mic. All the FM radio tuning coils are visible & a LT450GW electromechanical filter.

Radio PCB removed from the housing showing the main CPU controlling the unit, a Motorola MC13109FB.

The keypad PCB, with also holds the microphone & speaker.

Bottom of the keypad board, which holds a LSC526534DW 8-Bit µC & a AT93C46R serial EEPROM for phone number storage.

Here’s the base unit with it’s top cover removed. Black square object on far right of image is the microphone for intercom use, power supply section is top left, phone interface bottom left, FM radio is centre. Battery snap for power backup is bottom right.

PSU section of the board on the left here, 9v AC input socket at the bottom, with bridge rectifier diodes & main filter capacitor above. Two green transformers on the right are for audio impedance matching. Another LT450GW filter is visible at the top, part of the base unit FM transceiver.

Another 8-bit µC, this time a LSC526535P, paired with another AT93C46 EEPROM. Blue blob is 3.58MHz crystal resonator for the MCU clock. The SEC IC is a KS58015 4-bit binary to DTMF dialer IC. This is controlled by the µC.

Underside of the base unit Main PCB, showing the matching MC13109FB IC for the radio functions.

Tag: landline

Motorola Cordless DECT Phone Teardown

Southwestern Bell Freedom Phone