Ericsson GF768 Bedienungsanleitung

4/00021-2/FEA 209 544/6 C Troubleshooting guide

Troubleshooting guide.

GF 788/768/788e Standard.

Contents page

Component Classes 2

Abbreviations 3

Pin placements 4

1. RTC 6

2. Keyboard 8

3. Display 13

4. Charging 18

5. Illumination and buzzer 23

6. Doesn’t start 28

7. SIM fault 37

8. No serv 41

9. Audio 45

10. Spare part list 53

Troubleshooting guide 4/00021-2/FEA 209 544/6 C

Component classes.

All the components in the phone are divided into classes and after every component in the troubleshooting guide

you have a class written. The components are divided into four classes: A, B, C and D.The class of the component

depends on how much of the phone’s performance is affected when replacing it.

Class A and B: A test call towards the “real” net (not only towards a GSM test instrument) and run it through

the normal tests is enough to verify the functionality since the performance of the phone is only

slightly affected.

Class C: Since the tolerances of the component are so great it can substantially affect the performance of

the phone you need to calibrate it at station level after replacing the component.

Class D: Class D components need to be calibrated at board level using very advanced equipment and

may therefore not be replaced.

4/00021-2/FEA 209 544/6 C Troubleshooting guide

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.

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 determine if there’s any external

audio equipment attached.

EXTAUDI: The same signal as the EXTAUD signal but at the processor side.

GND: Ground.

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 determine 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.

RTC: Real time clock. The clock that keeps track of time and date.

SIMCLK: Clock signal from the processor used for communications with the SIM.

SIMDAT: Data signal from the processor used for communications with the SIM.

SIMRST: Reset signal from the processor used for communications with the SIM.

SIMVCC: Feed voltage for the SIM.

SWDC: Switched VBATT.

VANA: DC voltage for the analogue part of the logic (N800).

VBATT: Battery voltage.

VDIG: DC voltage for the processor and memory.

VDSP: DC voltage for the DSP (Digital Signal Processor).

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

VRAD: DC voltage for the radio part except the synthesizer.

VRPAD: DC voltage for the radio part in D600 (also used for the top diode and the buzzer).

VRTC: DC voltage for the real time clock.

VSIMPAD: VDIG voltage that has been switched up to 5V used for SIM.

VVCO: DC voltage for the synthesizer.

I2C: Two line serial communications standard using one clock and one data line.

LO: Local oscillator.

PWM: Pulse width modulation.

Troubleshooting guide 4/00021-2/FEA 209 544/6 C

Pin placements

Single diode (PIN diode). Electrolytic capacitor.

Double diode or single trans-

stor. Five pin circuit (usually volt-

age regulator). Double transistor.

Eight pin circuit. 688 VCO circuit 788 VCO circuit

Sixteen pin circuit Twenty pin circuit Crystal

4/00021-2/FEA 209 544/6 C Troubleshooting guide

N800 D900

D600

D620 D610

Troubleshooting guide 4/00021-2/FEA 209 544/6 C

1. RTC

1.1 Find the fault.

Start the phone with a SIM-card and a fully charged battery inserted. Set the correct time. Remove the battery and

reinsert it after a minute.

• If the clock says 00:00, go to 1.2.

Compare to the correct time.

• If the clock is speeding or if it is halted, go to 1.3.

The component side of the circuit board is shown in ﬁg. 1.1.

Fig. 1.1

1.2 The phone shows 00:00 after removing and reinserting the battery.

Open the phone and make sure that the backup capacitor, C720 (class A, ﬁg. 1.2), is correctly soldered.

Fig. 1.2

If it is, replace it. Assemble the phone, start it up and set the correct time. Wait a few minutes for the capacitor to

charge. Remove the battery and reinsert it after a minute. Check that the fault is ﬁxed (the backup capacitor needs

4/00021-2/FEA 209 544/6 C Troubleshooting guide

a few hours of charging to get fully charged). Compare to the correct time. If the clock is speeding or if it is

halted, go to 1.3.

1.3 The clock is speeding or is halted.

Open the phone and make sure the RTC crystal, B600, is correctly soldered. If it is, replace B600, C690 and C691

(all of them class A, ﬁg. 1.3). Assemble the phone and compare to the correct time.

Fig. 1.3

Troubleshooting guide 4/00021-2/FEA 209 544/6 C

2. Keyboard

2.1 Kind of keyboard fault.

Insert a SIM-card and a fully charged battery into the phone. Start the phone using the On/Off button. If it doesn’t

start at all, go to chapter 6.

Press all the keys (including the volume keys) and verify which of them that doesn’t work. Veriﬁcation is most

easily done like this:

1. Applies for GF 788/788e/788c:

Change the menu size to extended.

Go to “Settings/Key sound” in the menus and change to “click”.

Applies for GF 768/768c:

Go to “Key sound” in the menus and change to “click”.

2. Press the keys 1, 2, 3…*, 0, #. A clicking sound should be heard and the corresponding sign should be

shown in the display at every key pressed. Then press Yes, No, CLR, “<” and “>”. When pressing Yes the

phone should try to place a call, when pressing No it should disconnect it. Pressing CLR should make it

clear the display and “<” and “>” should make it scroll through the menus.

3. Press the volume keys. At every press there should be a clicking sound.

• If only the volume keys are non-functional, go to 2.2.

• If one or more keys are non-functional, go to 2.3

• If one or both of the volume keys and one or more of the other keys are non-functional, read both 2.2 and 2.3.

2.2 The volume keys are non-functional.

Open the phone and check for water damage, especially at the microswitches J820 and J821 (ﬁg. 2.1).

Fig. 2.1

Make sure the microswitches J820 and J821 (both of them class A) are intact and correctly soldered.

Measure the resistance of the microswitch that is broken. You measure from leg 1 or 3 to leg 2 or 4 (ﬁg. 2.2). The

resistance should be more than 100 kohms when not pressed and ~0 ohms when pressed.

4/00021-2/FEA 209 544/6 C Troubleshooting guide

Fig. 2.2

• If the resistance is high all the time, replace the corresponding microswitch.

• If the resistance is low all the time, replace the corresponding microswitch. If that doesn’t help, check the sol-

derings at D600 pads 1, 123, 124 and 128. If the solderings are correct, replace D600 (class B, ﬁg. 2.3).

Fig. 2.3

• If the switches work, replace the volume buttons and try again.

• If that doesn’t help, check the solderings at D600 pads 1, 123, 124 and 128. If the solderings are correct,

replace D600 (class B, ﬁg. 2.3).

2.3 One or more keys non-functional.

Open the phone and check for water damage. Remove the dome foil and check for water damage and mechanical

damage, especially at the non-functional keys.

Clean the key pads thoroughly. Mount a new dome foil and check the keyboard for damages. Assemble the phone

and check the kayboard function as described in 2.1.

If that doesn’t help, open the phone, give it power and start it up (using the On/Off key or by setting DCIO high).

Functional schematics are shown in ﬁg. 2.4.

Troubleshooting guide 4/00021-2/FEA 209 544/6 C

Fig. 2.4

Measure VDIG (ﬁg. 2.5, ~3.2V).

• If the voltage is incorrect, go to chapter 6.

• If it’s correct, check if there’s any voltage (~3.2V) at marked sides of R630, R631, R632, R633 and R634 (all

in ﬁg. 2.5).

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