Service Manuals, User Guides, Schematic Diagrams or docs for : . Rare and Ancient Equipment Ericsson Mobile Phones ERICSSON GF786, GF788, GF788E ERICSSON GF786, GF788, GF788E
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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
1
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.
2
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.
3
Troubleshooting guide 4/00021-2/FEA 209 544/6 C
Pin placements
Single diode (PIN diode). Electrolytic capacitor.
Double diode or single trans- Five pin circuit (usually volt- Double transistor.
stor. age regulator).
Eight pin circuit. 688 VCO circuit 788 VCO circuit
Sixteen pin circuit Twenty pin circuit Crystal
4
4/00021-2/FEA 209 544/6 C Troubleshooting guide
N800 D900
D600
D620 D610
5
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.
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