Lenovo YOGA Tablet 2-851F – Ac adapter test procedure – How to remove the case – How to check battery status

Lenovo YOGA Tablet 2-851F 

To verify a symptom, follow the steps below:
1. Turn off the computer.
2. Remove the battery pack.
3. Connect the AC adapter.
4. Make sure that power is supplied when you turn on the computer.
5. Turn off the computer.
6. Disconnect the AC adapter and install the charged battery pack.
7. Make sure that the battery pack supplies power when you turn on the computer.
If you suspect a power problem, see the appropriate one of the following power supply checkouts:
“Checking the Computer AC Charger”
“Checking the internal battery status”
Checking the Computer AC Charger
When you use the computer AC Charger to charge the tablet but no power is charged, see the instructions in this topic to check the computer AC Charger.
To check the computer AC Charger, do the following:
1. Disconnect the micro-USB cable from the tablet.
2. Measure the output voltage across the connector marked B of the micro-USB cable. Refer to the following figure:

Note: The output voltage across pin 3 of the micro-B connector might be different from the one you are servicing.

3. If the voltage is not correct, replace the micro-USB cable.

4. If the voltage is acceptable, replace the system board.

Checking the internal battery status
To check the battery status of the tablet, do either of the following:
Approximate information about the battery status
Get the approximate status of the battery at any time by checking the battery status icon on the system bar in the upper-right corner of the screen. The shorter the green bar is, the less the battery power remains.
Accurate information about the battery status
To get the accurate information about the battery status of the tablet, do the following:
1. Open the Android Settings screen.
To open the Android Settings screen, do either of the following:
From the main Home screen, touch the Android Settings icon on
Lenovo Launch Zone. The Android Settings screen is displayed.
Pull down the application icon from the action bar and then touch Settings. The Android Settings screen is displayed.
2. Touch Battery in the Device section on the Android Settings screen.
3. The accurate percentage of the remaining battery power is shown on the screen.

Disassembling procedure 

How to remove Rear cover
1. Open the hinge frame.

2. Open the card slot cover using a thin flat blade or guitar pick.

3. Remove screws 1 on the rear cover as shown in the figure below.

4. Separate the bottom right corner of the rear cover from the main body of the tablet using a suction tool as shown in the figure below.

5. Hold the tablet in one hand and use a guitar pick to unlock the rear cover from the tablet along the joint line as shown in the figure below.

6. Slowly remove the rear cover.

Telwin technica 150 inverter for welding – schematic – Part 2 of 2

Visual inspection of the machine
Make sure there is no mechanical deformation, dent, or damaged and/or disconnected connector.  Make sure the power supply cable has not been damaged or disconnected internally and that the fan works with the machine switched on. Inspect the components and cables for signs of burning or breaks that may endanger operation of the power source. Check the following elements:

Main power supply switch

Use the multimeter to check whether the contacts are stuck together or open. Probable cause:
- mechanical or electric shock (e.g. bridge rectifier or IGBT in short circuit, handling under load).

Current potentiometer R52

Probable cause:
- mechanical shock.

Relay K1

If the relay contacts are stuck together or dirty, do not attempt to separate them and clean them, just replace the relay.

Electrolytic capacitors C4,C5, C6, C7

Probable cause :
- mechanical shock;
- machine connected to power supply voltage much higher than the rated value;

broken rheophore on one or more capacitor: the remainder will be overstressed and become damaged by overheating;
- ageing after a considerable number of working hours;
- overheating caused by thermostatic capsule failure.

IGBT's Q1, Q2, Q3, Q4

Probable cause:
- discontinuation in snubber network;
- fault in driver circuit;
- poorly functioning thermal contact between IGBT and dissipator (e.g. loosened attachment screws: check);
- excessive overheating related to faulty operation.

Primary diodes D40, D41

Probable cause:
- excessive overheating related to faulty operation

Secondary diodes D20, D21, D22, D23

Probable cause:
- discontinuation in snubber network;
- poorly functioning thermal contact between IGBT and dissipator (e.g. loosened attachment screws: check);
- faulty output connection.

Power transformer and filter reactance

Inspect the windings for colour changes. Probable causes:
- power source connected to a higher voltage than 280Vac;
- ageing after a substantial number of working hours;
- excessive overheating related to faulty operation.

Checking the power and signal wiring

It is important to check that all the connections are in good  condition and the connectors are inserted and/or attached correctly. To do this, take the cables between finger and thumb (as close as possible to the fastons or connectors) and pull outwards gently: the cables should not come away from the fastons or connectors. N.B. If the power cables are not tight enough this could cause dangerous overheating.

Electrical measurements with the machine switched off

With the multimeter set in mode check the following components (junction voltages not less than 0.2V):
- rectifier bridge D1
- IGBT's Q1, Q2, Q3, Q4 (absence of short circuits between collector-gate and between emitter-collector );
- secondary board diodes D20, D21, D22, D23 between anode and cathode, The secondary diodes can be checked without removing the power board: with one prod on the secondary board dissipator diodes and the other in sequence on the two power transformer outlets;
- viper U2 (absence of short circuits between pin 3 - pin 4 and between pin 4 pin 2, )

With the multimeter set in ohm mode check the following
components:
- resistor R1: 47ohm (pre-charge );
- resistors R44, R45: 22ohm (primary snubber );
- resistor R20: 10ohm (secondary snubber );
- thermostat continuity test on the power transformer: clean the resin from the bump contacts of ST1 (A,B) and measure the resistance between the two bump contacts, it should be approx. 0 ohm.

if no signal is present, it may be necessary to replace the integrated circuit U2.

 Wiring diagram power board - power supply / control 

Wiring diagram - control board

Wiring diagram - change voltage board 115/230V (only for TECNICA)

Replacing the boards
If repairing the board is complicated or impossible, it should be completely replaced. The board is identified by a 6-digit code (printed in white on the component side after the initials TW). This is the reference code for requesting a replacement:
Telwin may supply boards that are compatible but with different codes.
Before inserting a new board check it carefully for damage that may have occurred in transit. When Technica supply a board it has already been tested and so if the fault is still present after it has been replaced correctly, check the other machine components. Unless specifically required by the procedure, never alter the board trimmers.

Before making the replacement make sure the components piloting the IGBT's are not also damaged:
- with the multimeter set in mode make sure there is no short circuit on the PCB between the 1 and 3 bump contacts (between gate and emitter) corresponding to each component;
- alternatively, resistors R40, R41, R42, R43 could have burst and/or diodes D32, D33, D34 and D35 may be unable to function at the correct Zener voltage (this should have shown up in the preliminary tests);
- clean any irregularity or dirt from the dissipaters. If the IGBT's have burst the dissipaters may have been irreversibly damaged: in this case they should be replaced;
- apply thermo-conductive grease following the general.

instructions.- Insert the new IGBT's between the dissipater and the spring, taking care not to damage the component during assembly (the spring should be inserted under pressure on the dissipater so as to lock the component);
- place the dissipaters with the new IGBT's and primary diodes D40 and D41 ( Make sure there is insulation between the case of diode D41 and the dissipater) in the PCB bump contacts, placing 4 spacers between the dissipater and the PCB (2 for each dissipater) and fasten them down with the screws (torque wrench setting for screws 1 Nm ±20%);
- solder the terminals taking care not to let the solder run along them;
- on the welding side cut away the protruding part of the rheofores and check they are not shorted (between the gate and emitter in particular).

The 4 SECONDARY DIODES are attached to the same dissipater, and when a replacement is required, all of them should be replaced:
- undo the screws attaching the dissipater to the board, to replace diodes D20, D21, D22 and D23;
- remove the 4 secondary diodes unsoldering the rheofores and cleaning any solder from the bump contacts on the board;
- remove the dissipater from the board;
- remove the spring locking the 4 diodes;
- clean any irregularity or dirt from the dissipater. If the diodes have burst the dissipater may have been irreversibly damaged: in this case it should be replaced;
- apply thermo-conductive grease following the general instructions;
- insert the new diodes between the dissipater and the spring, taking care not to damage the component during assembly (the screw should be inserted under pressure on the dissipater so as to lock the component);
- place the dissipater with the new components in the PCB bump contacts and fasten them down with the screws (torque wrench setting for screws 1 Nm ±20%);
- solder the terminals taking care not to let the solder run along them;
- on the soldering side cut away the protruding part of the rheofores and check they are not shorted (between cathode and anode); make sure resistor (R20) and capacitor (C20) on the snubber have been soldered to the PCB correctly.

TECNICA 150, 152, 170, 168GE Inverter troubleshooting - Part-1 of 2

Block diagram and descriptions

Block 1: EMC Filter

Consisting of: C1, C2, C3, L1.
Prevents noise from the machine from being transmitted along
the main power line and vice versa.

Block 2: Pre-charge

Consisting of: K1, R1.
Prevents the formation of high transitory currents that could damage the main power switch, the rectifier bridge and the electrolytic capacitors.
When the power source is switched on the relay K1 is deenergised, capacitors C4, C5, C6, C7, C8 are then charged by R1. When the capacitors are charged the relay is energized.

Block 3: Rectifier Bridge

Consisting of: D1.
Converts the mains alternating voltage into continuous pulsed voltage.

Block 4: Filter

Consisting of: C4, C5, C6, C7.
Converts the pulsed voltage from the rectifier bridge into continuous voltage.

Block 5: Chopper

Consisting of: Q1, Q2, Q3, Q4.
Converts the continuous voltage from the filter into a high frequency square wave capable of piloting the power transformer.
Regulates the power according to the required welding current/voltage.

Block 6: Current transformer

Consisting of: T2.
The C.T. is used to measure the current circulating in the power transformer primary and transmit the information to block 14 (primary current reader and limiter).

Block 7: Power transformer

Consisting of: T3.
Adjusts the voltage and current to values required for the welding procedure. Also forms galvanic separation of the primary from the secondary (welding circuit from the power supply line).

Block 8: Secondary diodes

D20, D21 converts the current circulating in the transformer to a single direction, preventing saturation of the nucleus.  D22, D23 recirculate the inductance output current (block 9) when the IGBT's are not conducting, bypassing the power transformer (block 7).

Block 9: Inductance

Consisting of: L2.
Levels the secondary board diodes’ output current making it practically continuous.

Block 10: Secondary EMC filter

Consisting of: C21, C22.
Prevents noise from the power source from being transmitted through the welding cables and vice versa.

Block 11: Flyback power supply

Consisting of: T1, U2.
Uses switching methods to transform and stabilise the voltage obtained from block 4 (filter) and supplies auxiliary voltage to power block 12 (driver) and the control board correctly.

Block 12: Driver

Consisting of: ISO2, ISO3.
Takes the signal from block 11 (flyback power supply) and, controlled by block 14 (duty cycle maker), makes the signal suitable for piloting block 6 (chopper).

Block 13: Primary current reader and limiter

Consisting of: R63, R64, R65 and part of the control section.  Reads the signal from block 6 (current transformer) and scales it down so it can be processed and compared in blocks 14 and 15.

Block 14: Duty cycle maker

Consisting of: U2 (control board).
Processes the information from block 15 (adder) and block 13 (primary current reader and limiter) and produces a square wave with variable duty cycle limiting the primary current to a maximum pre-set value under all circumstances.

Block 15: Adder

Consisting of: U1C (control board).
Gathers all the information from block 13 (primary current reader and limiter), from block 16 (alarms) and from block 18 (current potentiometer), and produces a signal with a suitable voltage for processing by block 14 (duty cycle maker).

Block 16: Alarm block

Consisting of: U1A, U1B (control board).
When an alarm is detected the power source output current is drastically reduced by making direct adjustments to block 14 (duty cycle maker) and directly changing the reference signal obtained from block 18 (current potentiometer).

Block 17: alarm LED

Consisting of: D14.
It is switched on by block 16 (alarms) in the event of:
1) Triggering of thermostatic capsule/thermostat on power transformer.
2) Triggering due to undervoltage.
3) Triggering due to overvoltage.
4) Short circuit at output (electrode holder clamp and earth cable connected to one another or electrode stuck to piece being welded).

Block 18: Current potentiometer

Consisting of: R52.
This is used to set the reference voltage needed to adjust the output current: when the potentiometer knob is turned the cursor voltage varies, thus varying the current from the minimum to the maximum value.

Block 19: max; current adjustment

Consisting of: R56, R57, R58.
Used to adjust the maximum cutting current to be supplied by the power source.

Block 20: Power transformer thermostat

Consisting of: ST1.
When the temperature of the power transformer is too high, the thermostat transmit the information to block 21 (galvanic separation). It is reset automatically after the alarm condition has ceased.

Block 21: Galvanic separator

Consisting of: ISO1.  The signal arriving from blocks 20 and 21 (power transformer thermostat and secondary diodes) is separated galvanically and sent to block 16 (alarms) for detection of a possible alarm event.

Block 22: Overvoltage safeguard

Consisting of: R71, R73 and part of the control section.
If the main supply voltage exceeds the maximum value this safeguard triggers (a tolerance of approx. ±15% of the power supply voltage is allowed: outside this range the safeguard triggers).

Block 23: Under voltage safeguard

Consisting of: R72, R70 and part of control board.
If the main supply voltage falls below the minimum allowed value this safeguard triggers (a tolerance of approx. ±15% of the power supply voltage is allowed: outside this range the safeguard triggers).

Block 24: Power supply identification 115/230V

Consisting of: U1A, Q2, Q1 (voltage change board).
This is only present on machines with the automatic identification function.
Identifies the power supply voltage level (115V or 230V) and compares the values with a reference signal. The comparison causes enabling of block 5 (filter) for operation in standard mode (230V) or as voltage duplicator (115V). This block also adjusts for the correct maximum current in relation to the different operating modes.

Block 25: Power supply LED

Consisting of: D12 (D13 for Tecnica 152).
Indicates when the power source is correctly powered and ready for use.
On machines operating exclusively at 230V it is green. On machines with automatic voltage identification (Tecnica 152) it is green for operation at 230V and orange for operation at 115V.

Block 26: Fan

Consisting of: V1.
Powered directly by block 13 (power supply) and cools the power components.

Troubleshooting details and schematic – by next post

Lenovo MIIX 3-830 Tablet – Disassembling procedure – How to remove the battery – How to test the AC Adapter

Lenovo MIIX 3-830 

To verify a symptom, follow the steps below:
1. Turn off the computer.
2. Connect the AC adapter.
3. Make sure that power is supplied when you turn on the computer.
4. Turn off the computer.
5. Disconnect the AC adapter.
6. Make sure that the battery pack supplies power when you turn on the computer.
If you suspect a power problem, see the appropriate one of the following power supply checkouts:
“Checking the AC adapter”
 “Checking operational charging”
Checking the AC adapter
You are here because the computer fails only when the AC adapter is used.
If the power-on indicator does not turn on, check the power cord of the AC adapter for correct continuity and installation.
To check the AC adapter
1. Unplug the AC adapter cable from the computer.
2. Measure the output voltage at the plug of the AC adapter cable. See the following figure:

Note: Output voltage for the AC adapter pin No. 2 may differ from the one you are servicing.

3. If the voltage is not correct, replace the AC adapter.
4. If the voltage is acceptable, do the following:
Replace the system board.
Note: Noise from the AC adapter does not always indicate a defect.
Checking operational charging
To check whether the battery charges properly during operation, use a discharged battery pack or a battery pack that has less than 50% of the total power remaining when installed in the computer.

Perform operational charging. If the battery status indicator or icon does not light on, remove the battery pack and let it return to room temperature. Reinstall the battery pack. If the charge indicator or icon is still off, replace the battery pack.
If the charge indicator still does not light on, replace the system board. Then reinstall the battery pack.

Restore of factory default

The Lenovo MIIX 3-830 computers come with a pre-installed Recovery system. In order to save application files and the initial backed-up files of the system, the hard disk in a Lenovo computer includes a hidden partition when it is shipped. If you need to restore the system to the point of your first boot up, just enter the Recovery System.

DISASSEMBLING PROCEDURE 

How to remove LCD cover
Note: To separate the LCD cover from the tablet, use a prying tool (such as a thin plastic plate).
Insert a prying tool between the base cover and the panel module and slide it around the tablet in the direction shown by arrows 1, 2 and 3 to separate the base cover from the rest of the tablet.

Then carefully remove the LCD cover in the direction shown by arrow 4.

How to remove Battery pack

Note: The battery pack is stuck to the LCD module. To separate the battery and the LCD module, use a piece of strong and thin string (such as fishing line).
Remove the tape that secures the battery connector. Then unplug the battery connector in the direction shown by arrow 1.
Note: Do not use too much force when you disconnect the battery connector, otherwise the connector or the cable may be damaged.

Insert a piece of string between the battery pack and LCD module. (from the right side of the battery).

While Pulling the string with both hands as shown by arrows 2, carefully move the string in the direction shown by arrow 3 to separate the battery from the LCD module.
Attention: The battery pack is thin and easy to distort or wrinkle. Please be careful when you remove it.

Remove the battery pack in the direction shown by arrow 4.