C926 Troubleshooting

KONKA Telecommunication R&D Center

2005

Confidential Page 1 2005-12-15

Version history

Ver Date Author Comments

0.00 11/01/05 Yuping Tang Draft

0.01 12/14/05 Yuping Tang Draft

Confidential Page 2 2005-12-15

1 Component Identification

1.1 About the troubleshooting

The mobile phone is complex electronic device, the aging of components, the abnormal
use of the mobile phone may course unknown problem. There are some ways help to find
out what the problems are. For example, you can exchange mobile components to locate
the problem, or you can use the some instruments to check them. We provide a command
[*#66*#] to verify the basic hardware functions.

1.2 Components Identification

Key component identify.

Baseband chip (MT6205B)

PMIC (MT6305)

RF Transceiver (MT6119)

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 TXVCO

VCTCXO 26MHz

RF Power Amplifier (RF3140)

Antenna Switch Module

Board-to-Board Connector

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 I/O Connector

RF Connector

Golden Capacitor

32KHz Crystal

2in1 Speaker

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 Vibrator

Microphone

FPC (Flexible Printed Circuited board)

Hinge

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2 C926 Troubleshooting

2.1 The common problems

1. No display, display white/blue screen.
[Diagnosis]:
The LCM (LCD Module) is connecting with Baseband circuit through a FPC (Flexible
Printed Circuit board); one of the LCM related connection has problem, it will cause
abnormal display, and the main reasons list as follow.
a) The functional fault of LCM.
b) The functional fault of FPC.
c) The functional fault of PCBA.
d) The connection problems at the both end of FPC.

[LCM connector]

2. Display black line (horizontal/vertical) on the screen.

[Diagnosis]:
The cause of back line is the connection problem inside the LCM, in this case we must
replace with a new LCD module.

3. Status LED doesn’t flash.

[Diagnosis]:
There are 3 colors status LED in the LCD module, 3 control lines connecting with
Baseband circuit through a FPC. The functional fault of LCM, FPC, and the PCBA maybe
the cause reason.

4. Keypad LED doesn’t work.

[Diagnosis]:
The keypad LED control by Baseband circuit, we can use the multi-meter or oscilloscope
to check the control signal, it is a PWM output signal.

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5. No ringing sound.
[Diagnosis]:
The 2in1 Speaker is mount at the upper case of C926, one for ringing, and the other one
for speech call Receiver. To locate the problem, we need to check resistance of the 2in1
Speaker, the Speaker(Blue) should be 8Ωand the Receiver(Red) should be 32Ω.

[Solder pad for Vibrator, Speaker and Receiver]

The electronic components mounted at upper case are connected through the FPC. We
can use multi-meter or oscilloscope to check the output signal at the solder pad, before we
can check the output signal, we must turn it on in factory mode, the item6 “Loud Spk”.

Tips: Key in *#66*# to enter the factory mode.

6. No speech
[Diagnosis]:
This case is similar to the ringing system, the speech is coming out through the 2in1
Speaker, and the red wire is the Receiver output. Check the resistance of the Receiver, it
should be 32Ω. If the resistance of Receiver is OK, then we need to check the output
signal at the solder pad. The output signal must be active in factory mode.

7. No vibration
[Diagnosis]:
As discuss previous, the electronic components mounted at upper case are connected
through the FPC. So we need to make a functional check of the vibrator, and then check
the LCM and FPC. If all this items being checked, and they all are okay, the problem will
be the Baseband circuit. We can also change a spare PCBA to prove this.

8. Clamshell detection failed

[Diagnosis]:
The clamshell mobile phone has a magnetic detection system. There is a magnetic sensor
(Hall sensor) in the Baseband circuit, and a piece of magnet in the upper case. The circuit
can detect the close and open states of clamshell. When detection fails, we need to check
if the magnet stone is still there? Is magnetism strong enough to being detect by the
circuit?

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[Magnet stone for clamshell detect]

9. Invalid key function

[Diagnosis]:
There are 3 cases, single key failed, columns or rows failed, all keys failed.
[Case1]
There maybe some dusts on the keypad surface or metal dome; clean them can solve this
problem.
[Case2]
This maybe the problems of Baseband circuit, the most case is pseudo soldering of BGA.
[Case3]
The mobile phone can detect one key presses and key releases, if one of the keys in press
status, the other key could not respond. The most case is the side-key problem, the key can be
released after press, and it maybe the functional fault of the key.

10. Cannot make outgoing calls

[Diagnosis]:
When happens, if the mobile phone shows “Check operator services”. You need to check the
Line Switching in Menu->Settings->Call Setup->Line Switching, this service provide by service
provider, there are Line1 and Line2, the default setting is Line 1.

11. Automatically power down

[Diagnosis]:
The C926 has the function of “Schedule Power On/Off”; some people didn’t know he/she
already set this function. Please check by following path, Menu->Settings->Phone
Setup->Schedule Power On/Off.

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12. Poor signal
[Diagnosis]:
All the mobile phone being calibrated and tested in factory, the cause reasons list as
follow.
a) Connection problem of antenna, you need to check the antenna pogo pin. See the
following picture for the detail. Is the screw loosening? Is the screw-holder cracked?
b) For the circuit problems, we can use the Agilent 8960 or CMU 200 from
Rohde&Schwarz to make the measurement.

[Antenna pogo pin]

13. Dead Phone

[Diagnosis]:
Dead phone means that the phone can’t respond for the user’s operation. As we know the
mobile phone is a complex electronic device, the cause reasons maybe the hardware
problem, software problem, and the network problem.
a) If the problem appears only once, and it can be eliminate by reboot, is acceptable
error.
b) If the problem appears frequently, it is unacceptable error, we can exchange the
hardware components (PCBA), or software upgrade.
c) Cannot be power on, it is fatal error; sometimes software upgrade can solve this
problem. The LCM and memory sharing the same data bus, the functional fault of
LCM also cause power on failed.

14. Charging problem

[Diagnosis]:
a) Cannot be charge; exchange with a new charger or a new battery to confirm the
problem.
b) Cannot fully charge, the problem maybe the battery fault. Exchange a new one to
make sure.
c) Error message, if the dirty battery pad will cause this problem, there 3 main

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 connections to the battery, the positive, the negative, and the battery temperature
detection pin, see the following picture for the detail.

[Battery Pin description]

15. Short standby time.

[Diagnosis]:
If the standby time is shorter much than normal, the aging of battery will cause standby
being shorter, exchange a new one to make sure. If it is main board, we need to check the
circuit, test the current consumption of the phone in ideal or calling state.

16. Phone lock.

[Diagnosis]:
Sometimes someone change the phone lock password, and forgot the password number.
This time you need to use the pc software to unlock the password.

17. Automatic Key lock

Sometimes someone didn’t know how to set this function, please check by the following
path: Menu-> Settings ->Security Setup -> Auto Keypad Lock, the default is None.

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