No Turn On - Debug Procedure; Internal Charger Test Debugging - Motorola T720 Service Manual

T720
TROUBLESHOOTING
The goal in trouble shooting is to quickly nar-
row down the possibilities to isolate a failure
to a single faulty component. This is espe-
cially important before deciding to replace a
large IC, filter or any component that is diffi-
culty or risky to replace. Sometimes the prob-
lem will be visually obvious. For example: a
cold solder joint, cracked chip, tombstone
parts etc., other times it will be necessary to
take some measurements.
NO TURN ON – DEBUG PROCEDURE
• Visual check – look for any damaged parts,
unsolder, Cold solder or missing parts
• Checking for short circuits – apply 4.4V
power supply with a 1A current limit through
the external connector. If the phone draws
more than 0.5A, check all the regulators sig-
nals for short to ground
• Check for the power B+ at C2102 or C2103,
if no B+ present replace U3800
• Place a zero ohm resistor at R2006
• Check the regulated output voltages
•.if the voltages on the regulators are not correct
Table 7:
Linear Regula- Nomi-
tor nal Volt-
age
VREG_MSMP 2.83V
VREG_MSMC 2.86V
VREG_MSMA 2.65V
VREG_IF 2.90V
VREG_TCXO 2.75V
reflow or replace U2000
• Check the RTC clock Y2000: check the
clock for 32.768 Khz signal if not present
check C2009,C2010, C2011 and C2023, then
replace Y2000
• Check the 19.2 Mhz clock signal at C2008 if
Remember to remove R2006 – zero ohm resistor
after the trouble shooting process.

Internal Charger Test Debugging

Phone must be in Phone T mode to analyze
charger.
In DMSS mode, the default state of the
charger is off unless a valid charger (fast or
mid rate) and battery (EPROM and Ther-
mistor present) are detected by software.
Charging circuitry (except for PM1000) is next
to battery contact block and not under any
shields.
When charger is disabled, the EXT_B+ current
should be ~150mA +/- 50mA. Otherwise battery
charge test current limits will be exceeded. This
failure may not be caused by the charger circuit.
When charger is enabled (using set DVT Option
command) with 3.6V battery connected,
EXT_B+ current should be at 1A for high current
test, and ~370 for mid rate current test. If not,
verify that EXT_B+ is >4.4V at CEBUS connec-
tor and battery voltage is 3.6V at the battery con-
tact block.
Location to
When charger is enabled, battery charge current
check
will be 1A – EXT_B+_Current for high rate, and
370mA – EXT_B+_Current for mid rate current
C2017
settings.
C2022
When charger is enabled, voltage on R2101
C2018
(side connected to U2101) should be at 1.5V.
This voltage is proportional to the EXT_B+ cur-
C2021
rent and is calculated by (EXT_B+_CURRENT/
C2019
CURRENT_LIMIT) * 1.5 where current limit is
either 1A or 0.370A.
6 2
Product Support Tools
not present replace U350
© 2002 Motorola, Inc.