Lenovo 20RK, Hardware Maintenance Manual

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Safety inspection guide
The purpose of this inspection guide is to assist you in identifying potentially unsafe conditions. As each
machine was designed and built, required safety items were installed to protect users and service
technicians from injury. This guide addresses only those items. You should use good judgment to identify
potential safety hazards due to attachment of non-ThinkPad features or options not covered by this
inspection guide.
If any unsafe conditions are present, you must determine how serious the apparent hazard could be and
whether you can continue without first correcting the problem.
Consider these conditions and the safety hazards they present:
• Electrical hazards, especially primary power (primary voltage on the frame can cause serious or fatal
electrical shock)
• Explosive hazards, such as a damaged CRT face or a bulging capacitor
• Mechanical hazards, such as loose or missing hardware
To determine whether there are any potentially unsafe conditions, use the following checklist at the
beginning of every service task. Begin the checks with the power off and the power cord disconnected.
Checklist:
1. Check exterior covers for damage (loose, broken, or sharp edges).
2. Turn off the computer.
3. Disable the built-in battery. For the instruction on how to disable the built-in battery, see “Disabling the
built-in battery” on page 42.
4. Disconnect the power cord.
5. Check the power cord for the following:
a. Make sure that a third-wire ground connector is in good condition. Use a meter to measure the third-
wire ground continuity. Ensure that the continuity between the external ground pin and the frame
ground is 0.1 ohm or less.
b. The power cord is the type specified in the parts list.
c. Insulation is not frayed or worn.
6. Remove the LCD module assembly.
7. Check for cracked or bulging built-in batteries.
8. Check for any obvious non-ThinkPad alterations. Use good judgment as to the safety of any non-
ThinkPad alterations.
9. Check inside the unit for any obvious unsafe conditions, such as metal filings, contamination, water or
other liquids, or signs of fire or smoke damage.
10. Check for worn, frayed, or pinched cables.
11. Check that the built-in battery fasteners (screws or rivets) have not been removed or tampered with.
Handling devices that are sensitive to electrostatic discharge
Any computer part containing transistors or integrated circuits (ICs) should be considered sensitive to
electrostatic discharge (ESD). ESD damage can occur when there is a difference in charge between objects.
Protect against ESD damage by equalizing the charge. So that the machine, the part, the work mat, and the
person handling the part are all at the same charge.
Chapter 1
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Safety information
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