Jeff's DIY

Advice on doing your own diagnosis and repair


Advice from the book Can I Do It Myself?


Electronics Repair

 

Common electronics faults and possible causes.

 

Device battery charge does not last as long as it originally did.

Even rechargeable batteries wear out. You can buy a new battery for almost anything and replace it yourself. Some of them pop right in, but others may require installation. Iphones are one example for which you have to use tools to open the phone and remove the battery. Buy the tools with the battery. If the battery is held in by adhesive, you may need to heat the adhesive with a heat gun or hair dryer to get the battery out without damaging the phone.

 

Computer is much slower than it used to be.

This can be due to insufficient random access memory (RAM). Software requires more and more RAM as technology advances to allow it. Check your system parameters to see how much RAM to you and check to spec to see how much it can handle. If possible and you want to keep the computer another year or more, upgrade the memory.

 

Front or back glass of phone is cracked.

Most phones on the market these days have replaceable glass and touch screens. Look for replacements online and google for the procedures. Youtube often has them. You may need a heat gun or at least a hair dryer in addition to the tools normally supplied with the LRU.

 

Desktop computer does nothing when you try to start it.

This can be due to a failed power supply. Replacing the power supply in a desktop us relatively easy, but you want to be sure that is the problem before buying a new one. Make sure AC power is getting to the power supply and that no DC power is showing in the cables coming out of the power supply, before buying a new one.

 

Computer will not boot.

There are a lot of possible reasons for this condition. I'm assuming the machine powers up and shows something on the monitor. If it will boot to safe mode, the problem is likely software. See if you can restore the software to before the last change. If you can get to a DOS window, run chkdsk on the hard drive to see if the boot sector is damaged. If it is, you may need a new hard drive. Data on the drive can be recovered by connecting it as slave to another computer. In fact, you can use another computer to run chkdsk on the drive, if you have one. If all this is OK or you cannot do chkdsk, see if you can boot a recovery disk of the operating system from the optical drive or an external hard drive. If none of that works, your processor may have failed. Some motherboards use a socket for the processor. In these cases, it is not difficult to replace. Make sure you apply thermal compound to the heat sink before reinstalling.

 

Addition of cards to desktop computer.

Desktop motherboards have slots to allow certain LRUs to be replaced or added. These slots may allow graphics cards, Ethernet cards, USB hubs, etc. Before buying a card, check to see what the interface is and whether or not there are spare slots for any new functionality you want to add. The cards are held in by a single screw on the back panel of the desktop. When handling circuit cards, always take care to discharge any static electricity to the frame of something grounded before handling a card. Use care when removing or installing cards, making sure the male and female interfaces are identical. Some interfaces are very similar but not identical to prevent use of an incorrect LRU. For example, DDR and DDR II memory interfaces use slightly different slots.

 

Circuit Board Repair.

Repairing circuit board electronics is most easily done when one has a wiring diagram and understands the basic operation of the device in disrepair. The novice may get lucky sometimes by merely spotting and replacing components that are obviously damaged, but often doing such only results in the new components burning up again; because the real cause of failure has not been found and repaired.

Understanding the function of the product and its components is often still not enough without a diagram, but an oscilloscope can help considerably. With an o-scope, you can trace a signal through the device to see what parts are working. The scope displays voltage over time. A DC voltage displays a horizontal line. An AC voltage displays as a sinusoid. An audio signal displays as a squiggly line somewhere between 20 and 20,000 Hz. After a signal passes through a power transistor, its voltage should be amplified many times. You must power up the device to read these signals, so be careful not to touch anything inside.

To remove a component from the circuit board, use some wicking and a soldering iron to get the solder off the leads that hold the components to the board. Don't use more heat than is needed to melt the solder. Use rosin-core solder to attach the new component.



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