Ericsson T28s Troubleshooting Manual

Brand: Ericsson

Model: T28s

Type: Troubleshooting Manual

This manual is also suitable for

T28SC

The Ericsson T28s is a compact and stylish mobile phone that offers a range of advanced features and capabilities. With its sleek design and user-friendly interface, the T28s is perfect for those who value both form and function. Here are just a few of the things you can do with your new Ericsson T28s:

Make and receive calls with crystal-clear audio quality.
Send and receive text messages with ease using the intuitive keypad.
Store up to 500 contacts in the phonebook, so you can easily stay in touch with friends, family, and colleagues.
Take and share photos with the built-in camera.
Play your favorite games and listen to your favorite music on the go with the integrated media player.

Make and receive calls with crystal-clear audio quality.
Send and receive text messages with ease using the intuitive keypad.
Store up to 500 contacts in the phonebook, so you can easily stay in touch with friends, family, and colleagues.
Take and share photos with the built-in camera.
Play your favorite games and listen to your favorite music on the go with the integrated media player.

Trouble Shooting Guide, Standard

4/00021-2/FEA 209 544/19 E Approved according to 1776-2/FEA 209 544

Trouble Shooting Guide, Standard

Applicable for T28s and T28sc

Contents

1 Explanations....................................................................................................................2

2 Network Problems...........................................................................................................5

3 On/Off Problems...........................................................................................................10

4 Audio Problems.............................................................................................................13

5 Display/illumination problems.....................................................................................17

6 Capacity/Charging Problems.......................................................................................21

7 SIM Problems................................................................................................................22

8 Key/Flip Problems.........................................................................................................23

9 Alert Problems...............................................................................................................25

10 Data Communication Problems...................................................................................27

11 Software Problems........................................................................................................27

12 Other Problems.............................................................................................................28

13 Revision History............................................................................................................29

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1 Explanations

For component placing see doc.1078-2/FEA 209 544/19.

Repeated Tests:

When the front has been removed most of the tests can be performed without the front

mounted.

1.1 Abbreviations

B: Crystal.

C: Capacitor.

D: Digital circuit.

F: Over voltage protection.

H: Buzzer, LED and pads for display.

J: Connector.

L: Coil.

N: Analogue circuit, power amplifier at some phones.

R: Resistor.

S: Keyboard pads.

U: BALUN Component that converts a balanced signal to an unbalanced or the other way

around.

V: Transistor, diode.

X: Contact surface on the circuit board.

Z: Filter.

DCIO: DC voltage through the system connector for charging.

GND: Ground.

LED3K: Logical signal that activates the background illumination.

ONSWAn: Voltage from the On/Off key that starts the phone.

RTC: Real Time Clock. The clock that keeps the track of time.

SIMCLK: Signal from the processor used for communication to SIM, clock signal.

SIMDAT: Signal from the processor used for communication to SIM, data signal.

SIMRST: Signal from the processor used for communication to SIM, reset signal.

SIMVCC: Feed voltage for SIM.

VBATT: Battery voltage. 3.70 ± 0.05 V

VCORE: DC voltage for the processor and memory at, for instance, stand by mode.

2.50 ± 0.10 V

VDIG: DC voltage for the processor and memory. 2.70 – 2.85 V

VDSPC: DC voltage for the DSP (Digital Signal Processor). 1.80 ± 0.10 V

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VLCD: DC voltage for the display that controls the contrast.

VRAD: DC voltage for the radio part except the synthesiser. 3.80 ±

0.20 V

V380B: DC voltage for the radio part. 3.80 ±

0.20 V

VRTC: DC voltage for the real time clock. 2.35 ±

0.15 V

VVCO: DC voltage for the synthesiser. 3.80 ±

0.10 V

I2C: Communications standard for two-way communication using only 2 wires,

clock and data.

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1.2 Pin Placing

Single diode (PIN diode) Electrolytic capacitor

Double diode or single

transistor

Five pin circuit (usually volt-

age regulator)

Double transistor Eight pin circuit

Ten pin circuit Sixteen pin circuit Crystal

N200 N234 N600

J603

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2 Network Problems

2.1 Find out if the fault is Rx- or Tx-related

Connect the phone to a GSM test instrument and try to get SERV at input signal strength of

-68.5 dBm.

If the phone does not get SERV, go to section 2.2.

If the phone gets SERV, go to section 2.3.

2.2 The phone does not get SERV

Open the phone and check for liquid damage.

Make sure the antenna connector (W100, Fig.2.1) is not incorrectly soldered, mechanically

damaged, dirty or oxidised. Clean, re-solder or replace if needed.

Measure the resistance in the Antenna Connector (Fig. 2.1). Do not press down the antenna

connector. The resistance should be less than 5 ohms.

Fig. 2.1

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Check the solder joints at N200, Z200 and Z201.

Measure the resistance at R220, R221, R222 and R223, (all 0 Ohm).

Replace if incorrect.

Measure the resistance over L200 and L201, (0 Ohm).

Replace if incorrect.

Check that C312 is correctly soldered.

Try to get SERV again with the settings mentioned above.

If the phone gets SERV, go to section 2.3.

If the phone still not get SERV, the fault probably is within the LO part or there are too large

losses in the signal path. It is also possible that the feed voltages are incorrect.

Open the phone.

Power up the board and start it by pressing the On/Off key.

Measure the VRAD voltage at C501, at the pin close to N700 (3.80 V).

If the voltage is incorrect, send the unit on according to the local company directives.

Measure the V380B voltage at C500, at the pin close to C421/C424 (3.80 V).

If the voltage is incorrect, send the unit on according to the local company directives.

Measure the VVCO voltage at pin 5 of N502 (3.80 V).

If the voltage is correct, measure the resistance over R362 (18 kohms) and R363 (100 ohms).

Replace if incorrect.

If both the resistances are correct, go to section 2.2.1.

If the voltage at pin 5 of N502 is incorrect, measure the voltage at pin 1 of N502. It shall be

more than 4.10 V.

If the voltage is correct, replace N502.

If the voltage at pin 1 of N502 is incorrect measure the resistance over R503 (0 ohm), L500 (0

ohm), C503 (> 100 kohms) and C502 (> 100 kohms).

Replace if incorrect.

If all the resistances are correct and the voltage at pin 1 of N502 is 3.70 V replace V500.

If the fault remains, send the unit on according to the local the company directives.

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2.2.1 Check the feed voltages

The VRAD voltage for N234:

Measure the voltage at pin 5 of N234 (3.80 V).

If the voltage is incorrect, measure the resistance of L211 (0 ohm).

If the resistance is incorrect, replace L211.

Measure the voltage at pin 47 of N234 (3.80 V).

If the voltage is incorrect, measure the resistance of R345 (18 ohms).

If the resistance is incorrect, replace R345.

Measure the voltage at pin 62 of N234 (3.80 V).

If the voltage is incorrect, measure the resistance of L370 (0 ohm).

If the resistance is incorrect, replace L370.

The VVCO voltage for D300:

Measure the voltage on R303, at the pin close to R346 (3.80 V).

If the voltage is incorrect, measure the resistance of R303 (18 ohms).

If the resistance is incorrect, replace R303.

Measure the voltage on R334, at the pin close to C333 (3.80 V).

If the voltage is incorrect, measure the resistance of R334 (10 ohms).

If the resistance is incorrect, replace R334.

If the fault remains, send the unit on according to the local company directives.

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2.3 Connect a call at –68.5dBm input signal and power

level 5

If you are able to connect a call, go to section 2.4.

If you are not able to connect a call, measure the resistance from VBATT to ground at the

Battery Connector (Fig.2.2). It should be more than 20 kohms. If the resistance is less, usually

only a few ohms there is probably a short circuit in N400.

If there is a short circuit in N400, send the unit on according to the local company directives.

Fig. 2.2

Open the phone and check for liquid damage.

Make sure the antenna connector (W100, Fig. 2.1) is not incorrectly soldered, mechanically

damaged, dirty or oxidised. Clean, re-solder or replace if needed.

Check the solder joints on N351.

Try to connect a call again.

If you were able to connect a call, go to section 2.4.

If you still are not able to connect a call, send the unit on according to the local company

directives.

2.4 Read the Rx-level while call is connected

Make sure the output power is 31-35 dBm, if the Rx-level value is 40 - 46 steps.

If that is correct there is probably nothing wrong with the phone.

Lower the input signal to –102 dBm and make sure the Rx-level value is 6-12 steps and the

Rx-quality value is 0-2 steps.

If RX-level and Rx-quality is correct, try to run the phone through the test again.

If the phone passes the test but you are not able to connect a call towards the “real” net, make

sure the phone has not been locked out of the system due to theft.

If Rx-level is correct and Rx-quality is high, send the unit on according to the local company

directives.

If the Rx-level value is too high the phone needs to be calibrated.

If the Rx-level value is less than 38 steps with an input signal of –68.5 dBm or less than 5

steps at an input signal of –102 dBm then the fault is Rx-related.

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Open the phone and check for liquid damage.

Make sure the antenna connector (W100, Fig. 2.1) is not incorrectly soldered, mechanically

damaged, dirty or oxidised. Clean, re-solder or replace if needed.

Check the solder joints at N200, Z200 and Z201.

Measure the resistance over L200 and L201 (0 ohm).

Replace if incorrect.

Remove L204 and measure the resistance from pin 2 of Z200 to ground (>100 kohms).

Usually the resistance is only a few ohms when Z200 is faulty.

If the resistance is incorrect, replace Z200 and mount L204.

If the fault remains, send the unit on according to the local company directives.

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3 On/Off Problems

3.1 Type of fault

Make a general visual inspection of the phone.

Make sure the battery connectors are intact, clean and fully functional.

Measure the resistance from VBATT to ground at the Battery Connector (Fig.3.1). It should

be more than 20 kohms. If the resistance is less, usually only a few ohms there is probably a

short circuit in N400.

If there is a short circuit in N400, send the unit on according to the local company directives.

Fig. 3.1

Make sure there is no liquid damage at the system connector.

Replace if needed.

Insert a fully charged battery and press the On/Off key.

If the phone starts without the On/Off key being pressed, go to section 3.2.

If the phone starts, check the charging function by connecting a charger to the system

connector.

If the charging function is faulty, go to chapter 6 Capacity/Charging Problems.

If the phone starts (lights the background illumination, asks for SIM/Pin, seeks net…) there is

probably nothing wrong with the phone or the fault is intermittent.

If the phone does not start, insert a dummy battery and keep the On/Off key pressed.

If the phone consumes more than 50mA, go to section 3.3.

If the phone consumes 15-30mA, go to section 3.4.

If the phone consumes less than 15 mA, go to section 3.5.

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3.2 Starts immediately after inserting a battery

Open the phone and check for liquid damage.

Replace the dome foil.

3.3 Consumes more than 50mA

Measure the resistance from VBATT to ground at the battery connector (Fig. 3.1). It should

be more than 20 kohms. If it is less, usually only a few ohms there is probably a short circuit

in N400.

If there is a short circuit in N400, send the unit on according to the local company directives.

Open the phone and check for liquid damage.

Power up the board and press the On/Off key.

Measure the voltage on V500, at the pin close to N700. It should be more than 4.10 V.

If the voltage is 3.7 V replace V500.

Try to flash the signal program into the phone.

If the fault remains, send the unit on according to the local company directives.

3.4 Consumes 15-30mA

Try to program the phone in the flash programmer.

Open the phone and check for liquid damage.

If programming the phone is impossible measure the resistance over R629 (10 kohms).

If the resistance is incorrect, replace R629.

If the resistance over R629 is correct measure the resistance over C615. It should be more

than 40 kohms.

If the resistance is less, replace V607.

If that does not help, replace C615.

If the resistance over C615 is correct, replace D610.

If the fault remains, send the unit on according to the local company directives.

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3.5 Consumes less than 15 mA

3.5.1 Consumes no current

Open the phone and check for liquid damage.

Make sure X100 is not dirty, damaged or incorrectly soldered.

Replace the dome foil.

Power up the board.

Measure the VBATT voltage on C400, at the pin close to C401 (3.70 V).

If the voltage is incorrect, replace X100.

If the voltage at C400 is correct, measure the voltage at pin 2 of V610 (3.65 ± 0.10 V).

If the voltage at pin 2 of V610 is correct, replace V610.

If the voltage at pin 2 of V610 is incorrect, send the unit on according to the local company

directives.

If the fault remains, send the unit on according to the local company directives.

3.5.2 Consumes less than 15 mA

Open the phone and check for liquid damage.

Power up the board and start it by pressing On/Off key.

Measure the VDIG voltage on C703, at the pin close to C834 (2.75 V).

If the voltage is incorrect, check that the resistance from C703, the pin close to C834, to

ground is more than 40 kohms.

If the resistance is correct send the unit on according to the local company directives.

If the resistance from C703 is incorrect, replace C703.

Measure the CORE voltage on C702, at the pin close to R701 (2.50 V).

If the voltage is incorrect measure the resistance from C702, the pin close to R701, to ground.

It should be more than 200 kohms.

If the resistance is correct send the unit on according to the local company directives.

If the resistance from C702 is incorrect, replace C702.

If VDIG and VCORE are correct measure the VDSP voltage (1.80 V) at N740 pin 5.

If the voltage is incorrect, replace N740.

If VDSP is incorrect after the replacement of N740, measure the resistance over C740 (>20

kohms) and R705 (0 ohm). Replace if incorrect.

If both the resistances are correct, send the unit on according to the local company directives.

If VDSP is incorrect after replacement of C740, replace D900.

If the fault remains, send the unit on according to the local company directives.

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4 Audio Problems

4.1 Type of fault

Connect a call from the phone that is to be tested (hereafter called the phone) to a fully

functional phone (hereafter called the reference phone).

Check that the microphone and the earphone of the phone works correctly.

If the phone sounds strange, go to section 4.7.

Connect a hands free unit to the system connector of the phone.

Check the functionality of the hands free by first talking into the reference phone while

listening to the hands free speaker and then talking into the hands free microphone while

listening to the earphone of the reference phone.

If it is only the earphone, of the phone, that has a little or no sound, go to section 4.2.

If neither the hands free speaker nor the earphone of the phone works, send the unit on

according to the local company directives.

If the sensitivity of the microphone is poor (little or no sound in the reference phone), go to

section 4.3.

If neither the hands free microphone nor the microphone of the phone works, send the unit on

according to the local company directives.

If neither the earphone nor the microphone of the examined phone works, send the unit on

according to the local company directives.

If the hands free microphone does not work, go to section 4.4.

If the hands free speaker is out of order, go to section 4.5.

If neither the hands free speaker nor the hands free microphone works, go to section 4.6.

4.2 Earphone out of order

Open the phone and check for liquid damage.

Replace the earphone with one you know is functional. Test the phone again.

If the fault remains, make sure that the X831 and X832 connectors are not mechanically

damaged or incorrectly soldered.

If the fault remains, send the unit on according to the local company directives.

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4.3 Microphone out of order

Replace the flip and try again.

Open the phone and check for liquid damage.

Make sure:

• X830 is not mechanically damaged or incorrectly soldered.

• The microphone cable is not mechanical damaged and check specially the connectors.

• The microphone cable is correctly connected to X830 and the flip.

If the fault remains, measure the resistances of R814 (0 ohm), R812, R817, R819 (1 kohm)

and R818 (20 kohms).

If all the resistances are correct, replace C818 and C819.

If the fault remains, send the unit on according to the local company directives.

4.4 Hands free microphone out of order

The fault arises when the audio path is interrupted somewhere between the hands free

microphone (connected through the system connector) and the input of N800. The audio path

is shown in Fig.4.1.

Fig. 4.1

Open the phone and check for liquid damage, especially around the system connector.

Make sure the system connector is not damaged or incorrectly soldered.

Make sure all the components in Fig. 4.1 (R814, R825, R802, R803, R805, R850, C810,

C812, C817, C835 and C850) are mounted at the circuit board.

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Measure the resistances of C810 (>60 kohms), C812 (>1 Mohm), C817 (>1 Mohm), R802

(3.9 kohms), R805 (15 kohms), R803 (1 kohm), R814 (0 ohm), R850 (47 kohms) and C850

(>90 kohms). Replace if incorrect.

If the fault remains, send the unit on according to the local company directives.

4.5 Hands free speaker out of order

The fault arises when the audio path is interrupted somewhere between the output of N800

and the hands free microphone (connected through the system connector). The audio path is

shown in Fig. 4.2.

Fig. 4.2

Open the phone and check for liquid damage, especially around the system connector.

Make sure the system connector is not damaged or incorrectly soldered.

Measure the resistances of R804 (100 kohms), R640 (10 ohms) and C813 (>1 Mohm).

Replace if incorrect.

Measure the resistance from C813, the pin close to C835, to pin 10 of J602 (10 ohms).

If the resistance is incorrect, replace R640.

If the fault remains, send the unit on according to the local company directives.

4.6 The hands free microphone and speaker out of order

Replace J602.

If the fault remains, send the unit on according to the local company directives.

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4.7 The phone sounds strange

If there is a noise when the illumination is on, replace N750.

If there is distortion or the sound is “chopped”, measure VDIG (2.75 V) at R900 and R902, at

the pins close to D900.

If the voltages are incorrect, measure the resistance of R900 and R902 (10 kohms). Replace if

incorrect.

If the resistances are correct, send the unit on according to the local company directives.

If the voltages are correct, measure the resistance of R904 (1.0 kohms), R914 (0 ohm), R907,

R908 and R909 (100 kohms). Replace if incorrect.

If the resistances are correct, replace D900.

If the fault remains, send the unit on according to the local company directives.

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5 Display/illumination problems

5.1 Display

Insert a fully charged battery into the phone and start it up by pressing the On/Off key.

If the phone does not start, go to chapter 3, On/off problems.

If the display is missing one or more segments, go to section 5.1.1.

If nothing shows in the display, go to section 5.1.2.

5.1.1 Segments are missing

Open the phone and check for liquid damage.

Replace the display.

5.1.2 Nothing shows in the display

Open the phone and check for liquid damage.

Replace the display.

If the fault remains, power up the board and start it up.

Measure the voltage at pin 1 of V611 (3.80 ± 0.20 V).

If the voltage is incorrect, measure the resistance of R639 (10 ohms).

If the resistance is incorrect, replace R639.

If the resistance is correct, replace C639.

If the fault remains, send the unit on according to the local company directives.

Measure the voltage at pin 2 of V608 (5.90 - 6.20 V).

If the voltage is incorrect, measure the resistance of C637 (>100 kohms).

If the resistance is too low, replace C637.

If the resistance of C637 is correct, measure the resistance of R610 (0 ohm).

If the resistance of R610 is incorrect, replace R610.

If the resistance of R610 is correct, replace V608 and V611.

If that does not help, replace C635 and C636.

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Measure the voltages on the display pads (H623).

Pad 1: VLCD 5.90 – 6.20 V

Pad 2: VDIG 2.75 V

Pad 3: I

CDAT 2.70 – 2.85 V

Pad 4: Gnd

Pad 5: I

CCLK 2.70 – 2.85 V

If I2CDAT or I2CCLK voltage is missing, check the VDIG voltage (2.75 V).

If the VDIG voltage is incorrect, go to chapter 3 (“On/off problems”).

If the VDIG voltage is correct, measure the resistances of R619 (6.8 kohms), R620 (6.8

kohms), R615 (0 ohm) and R614 (0 ohm).

If any of the resistances are incorrect, replace the corresponding resistor.

If there is no VLCD voltage, check the resistance from pad 1 of H623 to pin 2 of V608 (0

ohm).

If the resistance is incorrect there is a foil damage, send the unit on according to the local

company directives.

If the fault remains, send the unit on according to the local company directives.

5.2 Background light and LED

Insert a dummy battery and a SIM-card into the phone and start it up by pressing the On/Off

key.

If the background illumination does not light up at start, go to section 5.2.1.

Wait for the phone to get SERV (towards the test instrument or the net).

If the top indicator does not start to flash green when the phone has got SERV, go to section

5.2.2

When the phone has got SERV and the top indicator flash green, reduce the battery voltage to

3.2V. By doing that the top indicator should start to flash red, the battery indicator show an

empty flashing battery and the phone should warn with a beep.

If the battery indicator shows an empty flashing battery but the top indicator does not flash

red, proceed to section 5.2.2.

If none of the above mentioned things happen the phone needs a battery calibration.

Send the unit on according to the local company directives.

5.2.1 Background illumination glows faintly or does not work at all

Use the menu to set the light on (Settings/Profiles/Edit Profiles/Light/On).

Open the phone and check for liquid damage.

Wash around X750 if needed (Fig.5.1).

Replace the illumination panel.

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Fig. 5.1

Power up the board start and it up.

Measure the voltage at pin 10 of N750 (3.7 ± 0.05 V).

If the voltage is incorrect, measure the resistances of L750 (7 ohms), C751 (>1 Mohm) and

the resistance from L750, at the pin close to C667, to VBATT (0 ohms).

If any of the L750 or C751 resistances are incorrect, replace the corresponding component.

If the resistance from L750 to VBATT is incorrect there is a foil damage, send the unit on

according to the local company directives.

If the voltage at pin 10 of N750 is correct, measure the voltage at pin 5 of N750 (2.70–

2.85V).

If the voltage at pin 5 of N750 is correct, replace C752.

If the voltage at pin 5 of N750 is incorrect, measure the resistance from C703, at the pin close

to C834, to pin 5 of N750 (0 ohm).

If the resistance is incorrect there is a foil damage, send the unit on according to the local

company directives.

Measure the resistance of R750 (18 kohms at board revision up to R1D, 22 kohms at board

revision R1E and later).

If the resistance is incorrect, replace R750.

If the resistance is correct, replace N750.

If the fault remains, send the unit on according to the local company directives.

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5.2.2 Red or green top indicator out of order

Open the phone and check for liquid damage.

Make sure the double LED (H650) is not incorrectly soldered.

If the solder joint is correct, power up the board and start it by pressing the ON/Off key.

Measure the voltage at pin 1 of H650 (2.70 – 2.85 V).

If the voltage is correct, replace H650. Assemble the phone and test as described in section

5.2.

If the voltage at pin 1 of H650 is incorrect, measure the resistance of R646 (220 ohms).

If the resistance is incorrect, replace R646.

If the resistance is correct there is a foil damage, send the unit on according to the local

company directives.

If the fault remains, send the unit on according to the local company directives.

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Ericsson T28s Troubleshooting Manual

Brand: Ericsson

Model: T28s

Type: Troubleshooting Manual

This manual is also suitable for

T28SC

Make and receive calls with crystal-clear audio quality.
Send and receive text messages with ease using the intuitive keypad.
Store up to 500 contacts in the phonebook, so you can easily stay in touch with friends, family, and colleagues.
Take and share photos with the built-in camera.
Play your favorite games and listen to your favorite music on the go with the integrated media player.

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Ericsson T28s Troubleshooting Manual

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Ericsson T28s Troubleshooting Manual

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