ERICSSON T28 Trouble shooting

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

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

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.

Trouble Shooting Guide, Standard

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, r eset 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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Trouble Shooting Guide, Standard

VLCD: DC voltage for the display that controls the contrast. VRAD: DC voltage for the radio part except the synthesiser. 3.80 ± V380B: DC voltage for the radio part. 3.80 ± VRTC: DC voltage for the real time clock. 2.35 ± VVCO: DC voltage for the synthesiser. 3.80 ±

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

clock and data.

0.20 V

0.15 V

0.10 V

0.20 V

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1.2 Pin Placing

Trouble Shooting Guide, Standard

Single diode (PIN diode) Electrolytic capacitor

Five pin circuit (usually volt-

age regulator)

Ten pin circuit Sixteen pin circuit Crystal

Double transistor Eight pin circuit

Double diode or single

transistor

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.

Trouble Shooting Guide, Standard

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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Trouble Shooting Guide, Standard

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.

Trouble Shooting Guide, Standard

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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Trouble Shooting Guide, Standard

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 t he 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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Trouble Shooting Guide, Standard

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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