Ericsson GH 688 Guide

Approved according to 1776-2/FEA 209 544
Trouble-shooting
instruction
GH 688/GA 628
Standard electrical repairs
4/00021-2/FEA 209 544/1.G
GH688,GA628, Standard Electrical Repairs

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4/00021-2/FEA 209 544/1.G 2(112)
Table of contents
1 Conditions .......................................................................................... 3
1.1 Component classes. ......................................................................... 3
1.2 Abbreviations. ................................................................................. 4
1.3 Pin placements ................................................................................ 6
2 No serv or can´t place a call. ............................................................ 8
3 Doesn’t start. ................................................................................... 13
4 Audio. ............................................................................................... 22
5 Display. ............................................................................................ 30
6 Charging. ......................................................................................... 38
7 SIM fault (“Insert card”). .............................................................. 43
8 Keyboard. ........................................................................................ 48
9 Illumination and buzzer. ................................................................ 55
10 RTC .................................................................................................. 63
11 Component lists ............................................................................... 65
11.1 Explanation ................................................................................... 65
11.2 Mounting drawing tables ............................................................. 66
GH688 .............................................................................................. 66
GA628 .............................................................................................. 66
11.3 Component list GH688 ................................................................. 67
11.3.1 Revision change tables GH688 ......................................................... 80
Revision change table for
2/ROA 117 3307/1 and 2/ROA 117 3307/5, 2/ROA 117 3307/3 80
Revision change table for
2/ROA 117 3307/4 2/ROA 11 73307/6 ............. 84
11.4 Component list GA628 ................................................................. 88
11.4.1 Revision change tables GA628 ....................................................... 100
Revision change table for
2/ROA 117 3308/1, 2/ROA 117 3308/2 .......... 100
Revision change table for
2/ROA 117 3308/3, 2/ROA 117 3308/4 .......... 104
Revision change table for
2/ROA 117 3308/5, 2/ROA 117 3308/7 .......... 109

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1 Conditions
1.1 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.

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

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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.

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1.3 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. VCO circuit Crystal
Sixteen pin circuit Twenty pin circuit

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N800 D900
D600
D620 D610

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2 No serv or can´t place a call.
2.1 Find out if the problem is Tx- or Rx-related.
Connect the phone (with signaling program) to a GSM instrument and try to get
serv at –68.5dBm signal strength.
• If the phone gets serv proceed to section 2.2.
• If it doesn’t get serv it’s probably a problem located in the LO-part or the losses
in the signal path are too great.
Open the phone and check for liquid damage.
The component side of the board is shown in fig. 2.1.
Fig. 2.1
Check the antenna connector, X401 (class A, fig. 2.2), and make sure that it isn’t
damaged or dirty (glue, varnish, oxide…) and that the solderings aren’t faulty.
Fig. 2.2
Look for faulty solderings at G350 and C359 (fig. 2.3).

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Fig. 2.3
Measure the resistance of C853 (class B, >100 kohms, fig. 2.4).
Fig. 2.4
Give the board power and start it up.
Measure VVCO (~3.8V) at V451 pad 3 and VRAD (~3.8V) at C457 (fig. 2.5).
• If any of the voltages are incorrect, proceed to chapter 3 (“Doesn´t start”-fault).

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Fig. 2.5
Measure the DC voltage at pin 1 and 2 of G350. The voltage at pin 1 (control volt-
age) should always vary between ~0.8V - ~2.8V (usually starts at ~1.7V). The volt-
age at pin 2 (feed voltage) also varies but usually starts at ~3.3V (fig. 2.3).
• If the feed voltage is incorrect (usually no voltage at all), check the soldering at
D600 pin 102 (fig. 2.1).
* If the soldering isn’t faulty, send the phone to the next level.
• If the control voltage is incorrect (usually ~0V or ~3.6V), check if C370 (class
B) and R357 (class B) are mounted (both of them in fig. 2.3).
* If that is the case, replace N350 (class B, fig. 2.3).
* If that doesn’t help, replace G350 (class B, fig. 2.3).
Measure the resistance of C540, C541, C542, C543, C544 and C545 (all of them
class B, >200 kohms, fig. 2.3)
Check the solderings at C826 (fig. 2.4), Z201, Z500, Z501 and Z502 (fig. 2.3).
If the problem isn’t solved, send the phone to the next level.
2.2 Connect a call at powerlevel 5 using an
instrument with –68.5dBm signal strength.
• If it works, proceed to section 2.3.
• If it doesn’t work, open the phone and check for liquid damage. Make sure the
ground foil around the antenna connector isn’t dirty.
Check the antenna connector, X401 (class A, fig. 2.2), and make sure that it isn’t
damaged or dirty (glue, varnish, oxide…) and that the solderings aren’t faulty.
Replace the back cover and try again.
• If it doesn’t work it most likely means that the problem is Tx-related.
Check if C300, C403, L300, V300, V301 or V302 (all class A, fig. 2.6) are burnt.

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Fig. 2.6
Check soldering at G300 (fig. 2.5).
Measure the resistance of C853 (class B, >100 kohms, fig. 2.4).
Measure the resistance of R403 (class B, <1 ohms, fig. 2.6).
Measure the resistance of L300 (class A, <1 ohms, fig. 2.6).
If the problem isn’t solved, send the phone to the next level.
2.3 Read the Rx-level and output power values
from the instrument while the call is still
connected.
• If the Rx-level value is at 40 - 46 steps, check that the output power is 31-
35dBm.
* If it is correct it means that the phone probably isn’t faulty. Lower the signal
strength at the instrument to –102dBm and make sure that the Rx-level value
is 6-12 steps and that the Rx-quality value is 0-2 steps.
* Try running the phone through the test again.
* If the phone passes the test but doesn’t manage to connect a call at
the “real” net, make sure that it isn’t because it is stolen. If it isn’t,
replace D600 (class B, fig. 2.1).
* If you get one of these error messages; “phase and frequency
error”, “burst timing”, “power level 5-19”, ”Rx-quality” or “Rx-
level” that differs slightly from the default values, try replacing the

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back cover and run the phone through the test again. This applies espe-
cially for the GA 628.
• If the output power is too low or the Rx-quality value is too high, send the phone
to the next level.
• If the Rx-level value is too high, the phone has to be calibrated and therefore you
have to send the phone to the next level.
• If the Rx-level value is below 40 steps at –68.5dBm signal strength or below 6
steps at –102dBm signal strength, the problem is Rx-related.
Open the phone and check for liquid damage.
Check the antenna connector, X401 (class A, fig. 2.2), and make sure that it isn’t
damaged or dirty (glue, varnish, oxide…) and that the solderings aren’t faulty.
Measure the resistance from C426 (fig. 2.2, measure from the marked side) to
ground (>1 Mohms). The resistance is usually only a few ohms when Z200 (class B,
fig. 2.7) is broken.
Fig. 2.7
Measure the resistance from the anode of V403 (class B, fig. 2.2) to ground (~60
kohms).
• If it’s less (a few kohms), lift one of the V402 pins from the pad and measure
again at the same place.
If it’s correct (~60 kohms), replace V402.
• If the resistance is still too low, replace both diodes.
Measure again after replacing the component(s).
• If the resistance is still too low, measure the resistance of R421 and R422 (both
of class B, 100 kohms, fig. 2.2). Both the resistors are 100 kohms but when you
measure them the instrument will show ~60 kohms.
Check the solderings at C826 (fig. 2.4), Z201, Z500, Z501 and Z502 (fig. 2.3).
Measure the resistance of C540, C541, C542, C543, C544 and C545 (all of them
class B, >200 kohms, fig. 2.3)
If the problem isn’t solved, send the phone to the next level.

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3 Doesn’t start.
3.1 Find out if the phone will start by using the
On/Off-button.
Insert a fully charged battery and press the On/Off-button.
• If the phone doesn’t start, proceed to section 3.2
• If the phone starts, check the charging function by connecting a charger at the
system connector.
If the phone doesn’t charge, proceed to chapter 6 (“Charging”-fault).
If the phone starts (lights the background illumination, asks for SIM/PIN,
seeks the net…) and charges it’s probably not faulty or the problem is inter-
mittent.
Open the phone and make a visual examination of the circuit board.
The component side of the board is shown in fig. 3.1.
Fig. 3.1
Check for liquid damages anywhere at the board. Also check for burnt or damaged
pads at the system connector and faulty soldering at, for instance, D600, D610 and
D620 (fig. 3.2).

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GH688
GA 628
Fig. 3.2
As soon as the problem is solved, send the phone through the flow as usual.

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3.2 Visual check.
Make a visual check. Make sure that the battery screws are intact and properly
mounted, that the isolator sleeve (GH 688) is properly mounted, that the volume
keys aren’t stuck and that the system connector isn’t dirty or liquid damaged. Con-
tinue at 3.3.
3.3 Current consumption with On/off-key
pressed.
Insert a dummy battery.
• If the phone consumes current immediately it usually means that C403 (class A,
fig. 3.3) is faulty but first you should make sure that the frame gasket isn’t in con-
tact with the positive battery connector pad at the circuit board (fig. 3.4).
Fig. 3.3
Fig. 3.4

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Start the phone using the On/Off-key and check the current consumption.
• If the phone doesn’t consume any current at all when the On/Off-key is
pressed it is most likely liquid damaged. Open the phone and check this. Also
check that the keyboard and the keyboard pads are functional and clean.
• If the phone consumes more than 200mA, remove the display elastomer and try
again.
* If the consumption is reduced it was probably the elastomer or the display.
* If the consumption is just as high as before, proceed to section 3.4.3.
• If the phone consumes ~60mA (average, varies), the battery indicator blinks
once or twice and then the phone turns itself off, then it’s probably X820 (the
pads to the volume flex film, fig. 3.5) or the volume flex film (J820) that is
shorted out. Replace the flex film and if that doesn’t work, proceed to section
3.2.
* If the same phenomena arises without the On/Off-key being pressed it
means that V704 is broken (fig. 3.2).
Fig. 3.5
• If the phone consumes 1-200mA, starts (asks for SIM/searches for the
net…etc…) and works as long as you keep the On/Off-key pressed, proceed to
section 3.4.4.
• If the phone doesn’t start, try to program it in the flash programmer.
* If it doesn’t start in the flash programmer, proceed to section 3.4.1
* If you are able to program the phone in the flash programmer but it doesn’t
start afterwards or if it is troublesome when trying to program it, proceed to
section 3.4.2.
* If the phone starts after programming it in the flash-programmer then the
problem is probably solved, but to eliminate intermittent errors check the cir-
cuit board for liquid damage or faulty solderings on D600, D610 and D620
(fig. 3.2).

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3.4 Measuring at a powered circuit board.
3.4.1 Doesn’t start in the flash programmer.
Open the phone and check for liquid damage.
Make sure the system connector pads aren’t burnt.
Place the board in the fixture. Start it up and keep it running by keeping DCIO high.
Check VDIG and VDSP voltages (~3.2 V, fig. 3.2).
• If any of the voltages are too low, measure the resistance to ground (VDIG > 500
ohms, VDSP > 25 kohms).
* If the resistances are correct, replace the corresponding circuit (VDIG –
N702, VDSP – N701, both of class A).
* If the resistance is too low, send the phone to next level.
• If any of the voltages are too high, replace the corresponding circuit.
Check the power reset voltage at C710 (fig. 3.2, >3V).
• If it’s lower, replace N450 (class A, fig. 3.6) and try again.
* If it didn’t work, replace C710 (class A).
Fig. 3.6
Check VRAD, VVCO and VRPAD (~3.8V, fig. 3.6).
• If all three voltages are wrong, measure the resistance from N450 pads 8, 11, 12,
13 and 14 to ground (~0 ohms).
* If the resistance is too high there is a foil damage and the phone is to be dis-
carded.
* If it is correct, replace the circuit and eventually the transistors (V452,
V451 and V450, all of them class A).
• If one or two of the voltages are wrong, measure the resistance from the corre-
sponding voltage source to ground (>50 kohms).
* If the resistance is correct, replace the corresponding transistor.

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* If that doesn’t help, replace N450 (class A).
* If the resistance of any of the voltage sources is too low, send the phone to
the next level.
Measure the amplitude of B551 pin 3 (class C, >1V t-t) with an oscilloscope, spec-
trum analyzer, frequency counter, diode probe…
• If the amplitude is too low, send the phone to the next level.
Check for bad solderings at D600, D610 and D620 (fig 3.2).
• If they look ok, replace D600 (class B).
* If that doesn’t work, first replace D610 (class A) and then D620 (class A).
Try to program the phone in the flash programmer for every circuit you
replace. Don’t replace any circuit if you haven’t established the fact that
B551 is working.
3.4.2 Is programmable in the flash programmer but
doesn’t start afterwards or is troublesome in the
flash programmer.
Open the phone and check for liquid damages.
Make sure the system connector pads aren’t burnt.
Insert the board in the fixture. Start it up and keep it going by keeping DCIO high.
Check VDIG and VDSP (~3.2V, fig. 3.2).
• If any of the voltages are too low, measure the resistance from it to ground
(VDIG >500 Ohms, VDSP >25 kohms).
* If the resistance is correct, replace the corresponding circuit (VDIG – N702
– class A, VDSP – N701 – class A).
* If the resistance is too low, send the phone to the next level.
• If any of the voltages are too high, replace the corresponding circuit.
Check VRAD, VVCO and VRPAD (~3.8V, fig. 3.6).
• If all the voltages are incorrect, measure the resistance from N450 pads 8, 11, 12,
13 and 14 to ground (~0 ohms).
* If any of the resistances are too high there is a foil damage and the phone
should be discarded.
* If all the resistances are correct, replace the circuit and eventually the tran-
sistors (V450, V451, V452, all class A).
• If one or two of the voltages are incorrect, measure the resistance from the incor-
rect voltage(s) to ground (>50 kohms).
* If the resistance is correct replace the corresponding transistor. If that
doesn’t help, replace N450 (class A).

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* If the resistances from any of the voltages to ground are too low, send the
phone to the next level.
Make sure that there are no faulty solderings on D600, D610 and D620.
• If the solderings look good, replace D610 (class A).
* If that doesn’t help, first replace D600 (class B) and then D620 (class A).
Try to program the phone in the flash programmer for every circuit you
replace.
3.4.3 Consumes more than 200mA.
Open the phone and check for liquid damage.
Make sure that the system connector pads aren’t burnt.
Insert the board in the fixture. Start it up and keep it going by keeping DCIO high.
Check VDIG and VDSP (~3.2V, fig. 3.2).
• If any of the voltages are too low, measure the resistance from it to ground
(VDIG >500 ohms, VDSP >25 kohms).
* If the resistance is correct, replace the corresponding circuit (VDIG – N702
– class A, VDSP – N701 – class A).
* If the resistance is too low, send the phone to the next level.
• If any of the voltages are too high, replace the corresponding circuit.
Check VRAD, VVCO and VRPAD (~3.8V, fig. 3.6).
• If all three voltages are incorrect, measure the resistance from N450 pads 8, 11,
12, 13 and 14 to ground (0 ohms).
* If the resistance is too high there is a foil damage and the phone should be
discarded.
* If the resistance is correct, replace the circuit and eventually transistors
(V450, V451, V452, all class A).
• If one or two of the voltages are incorrect, measure the resistance to ground (>50
kohms).
* If the resistance is correct, replace the corresponding transistor.
* If that doesn’t help, replace N450 (class A).
* If the resistance from any of the voltages to ground is too low, send the
phone to the next level.

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3.4.4 The phone works as long as the On/Off-key is
pressed.
GH688
Open the phone and check for liquid damages.
Make sure the system connector pads aren’t burnt.
Insert the board in the fixture. Start it up and keep it going by keeping DCIO high.
Measure the voltage at C692 (~3.1V, fig. 3.2).
• If there is voltage, check the soldering at D600 pin 119.
• If there isn’t voltage, measure the resistance of C692 (class A, >200 kohms).
* If the resistance is correct, measure the input voltage at N706 pin 2
(VBATT) and the output voltage at N706 pin 3 (~3.5V). Make sure that the
regulator has ground at N706 pin 1. There is a foil damage if the ground or
VBATT is missing at N706 and the phone should be discarded.
* If the input voltage and the ground are correct, replace N706 (class A).
* If the output voltage is correct, measure the voltage at the positive side
of the backup capacitor (C720, class A, ~3.1V).
* If there is no voltage, replace V711 (class A).
* If there is voltage, check the resistance from the positive side of C720
(fig. 3.5) to C692 (~0 ohms).
* If the resistance is too high there is a foil damage and the phone
should be discarded.
GA 628
Open the phone and check for liquid damage.
Make sure that the system connector pads aren’t burnt.
Insert the board in the fixture. Start it up and keep it going by keeping DCIO high.
Measure the voltage at C692 (~3.1V, fig. 3.2, the figure shows a GH 688 board but
the capacitor is placed at the same location).
• If there is voltage, check the soldering at D600 pad 119.
• If there is no voltage, measure the resistance of C692 (class A, >200 kohms).
* If the resistance is correct, measure VDIG.
* If the voltage at VDIG is incorrect, see 3.4.1, 3.4.2 or 3.4.3.
* If VDIG is correct, check the resistance from N702 pin5 (fig. 3.2) to
C692 (~0 ohms).