Ericsson T18s Guide

Approved according to 1776-2/FEA 209 544
Trouble-shooting
instruction
T18s, T18sc
Standard electrical repairs
4/00021-2/FEA 209 544/12.B
T18s, T18sc Standard Electrical Repairs

T18s, T18sc Standard Electrical Repairs
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Table of contents
1 Conditions .......................................................................................... 3
2 No SERV/Not able to connect calls. ............................................... 6
3 Doesn’t start. ................................................................................... 12
4 Audio. ............................................................................................... 21
5 Display. ............................................................................................ 30
6 Charging fault ................................................................................. 34
7 SIM fault ("Insert card") ............................................................... 38
8 Keyboard ......................................................................................... 45
9 Illumination, buzzer and vibrator. ................................................ 48
10 RTC .................................................................................................. 57
11 Component list ................................................................................ 59

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1 Conditions
1.1 Component classifications.
After each component, which fault can be verified by the trouble-shooting instruc-
tions in this folder, the classification of the component is written. The components
are divided into four classes, A,B,C and D. The classes are seperated depending on
how much of the prestanda of the phone that is affected by replacing the component.
Class A and B:Replacing the component doesn´t affect the prestanda that much,
you only have to do a test call towards a real network before you per-
form a function test after the exchange.
Class C: The phone has to be calibrated at station level after replacing the com-
ponent, since the components tolerances are so large it can affect the
prestanda of the phone.
Class D: It demands advanced equipment and calibration at board level and
because of that class D-components won´t be replaced.

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1.2 Abbreviations.
A: The power module at some phones.
B: Crystal.
C: Capacitor.
D: Digital circuit.
F: Over voltage protection.
G: VCO.
H: Buzzer, LED, pads for display.
J: Connector.
L: Coil.
N: Analogue circuit, the power module at some phones.
R: Resistor.
S: Keyboard pads.
U: BALUN. A circuit that converts a signal from balanced to unbalanced or the
opposite.
V: Transistor or diode.
X: Contact surface at the circuit board.
Z: Filter.
AGND: Ground for analogue signals.
DCIO: DC voltage used for charging the battery through the system connector.
DCON: Logical signal from the processor that keeps the phone running after
you’ve released the On/Off key.
EXTAUD: Input signal at the system connector that the processor uses to deter-
mine if there’s any external audio equipment attached.
EXTAUDI: The same signal as the EXTAUD signal but at the processor side.
GND: Ground.
LED1G and LED2R:Logical signal used to activate the green or red top indicator.
LED3K: Logical signal used to activate the background illumination.
ONSRQ: Voltage from the On/Off key that starts the phone.
PORTHF: Input signal at the system connector that the processor uses to deter-
mine if there’s any handsfree equipment attached.
PHF1: The same signal as PORTHF but at the processor side.
REGON: Logical signal that activates the voltage regulators.

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RTC: Real time clock. The clock that keeps track of time and date.
SIMCLK: Clock signal from the processor, through D901, used for communica-
tions with the SIM.
SIMDAT: Data signal from the processor, through D901, used for communica-
tions with the SIM.
SIMRST: Reset signal from the processor, through D901, used for communica-
tions with the SIM.
SIMVCC: The up switched VDIG, 5 V (in D901), used for the SIM.
VBATT: Battery voltage, 4.8 V.
VBUZZ: Feed voltage to the voltage transformer for the display (becomes
VLCD and VLCDMEAS).
VCORE: Feed voltage to D600 and D900, 2.5 V.
VDIG: DC voltage for the processor and memory, 3.2 V.
VLCD: DC voltage for the display that controls the contrast.
VLCDMEAS:The same as above, but is used in N800 to measure the voltage.
VRAD: DC voltage for the radio part except the synthesizer, 3.8 V.
VRPAD: DC voltage for the radio part in D600, 3.2 V.
VRTC: DC voltage for the real time clock, 3.1 V, also existing when the phone
is powered off..
VVCO: DC voltage for the synthesizer, 3.8 V.
VVIC: Feed voltage to D901 (SIM-controller circuit), 3.2 V).
I2C: Two line serial communications standard using one clock and one data
line.
LO: Local oscillator.
PWM: Pulse width modulation.

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2 No SERV/Not able to connect calls.
2.1 Find out if the fault is Rx or Tx related.
Connect the phone (with signalling program) to a GSM test instrument and try to
get SERV at –68.5dBm signal strength. Check both bands (GSM 900 and 1800).
• If the phone doesn’t get SERV at any of the bands, proceed to section 2.2.
• If the phone gets SERV at the GSM 900 or the GSM 1800 band, proceed to sec-
tion 2.4.
• If the phone gets SERV but you’re not able to connect calls at any of the bands,
proceed to section 2.3.
2.2 The phone doesn’t get SERV.
Open the phone and check for liquid damages.
Make sure the back cover isn’t broken or of the wrong model since there are two to
choose from. Fig. 2.1 shows what model of back cover is to be used.
Fig. 2.1
Replace the antenna connector. Note that there are several models to choose from
and you must use the correct model. Fig. 2.2 shows what antenna connector model
is to be used.
Fig. 2.2

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Try again to get SERV at –102dBm.
• If the phone gets SERV at –102dBm there’s probably nothing wrong with the
phone. Run the phone through the final test (Go/No go-test).
Open the phone.
Give the board power and start it up by pressing the On/Off key.
Measure the VVCO voltage at pin 5 of N470 (fig. 2.3, ~3.8V).
• If the voltage is too low, replace N470 and C472 (both of class A and in fig. 2.3).
* If the voltage still is too low, send the phone to Advanced electrical
repairs.
Measure the resistances of C541-C546 (>200 kohms, fig. 2.3).
• If the resistance of any of the capacitors is too low, replace the corresponding
capacitor.
Check the solderings of Z530, C531 and L530 (fig. 2.3).
If the fault remains, send the phone to advanced electrical repairs.

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Fig. 2.3

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2.3 Connect a call at powerlevel 5 towards the
instrument with an input signal of –
68.5dBm.
If you’re not able to connect a call, open the phone and check for liquid damages.
Make sure the back cover isn’t broken and that it is of the correct model as there are
two to choose from (fig. 2.1).
Replace the antenna connector (if it hasn’t been replaced before) and try again. Note
that there are several models to choose from and it’s important to mount the correct
one (fig.2.2).
If the phone still doesn’t work then the fault is most likely Tx-related or there’s a
feed voltage fault.

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Fig. 2.4
Give the board power and start it up (in the fixture).
Measure the VRAD voltage at C482 (~3.8V, fig. 2.3).
• If the voltage is incorrect, replace N480 (class A, fig. 2.3).
Check the solderings of G300 and Z440 (fig. 2.4).
Make sure L301, C392 and V301 (fig. 2.4) aren’t burnt.
If the fault remains, send the phone to Advanced electrical repairs.