help! how to diagnose smd components if its good or bad

[naruto11]

masters can you help me , how to diagnose smd components if its good or bad
or any site that has tutorial in smd electronics how to test smd electronics and identifying smd components also best electronics equiptment to be used

thanks to all who would give me some tips

 

[Sceadwian]

Lots and lots of experience... Use Google to search and know what the circuit the chip is in is designed to do to help you search properly. There is no magic tool, or best site to go to, there are massive amounts of SMD components, many with no markings, identifying them is an art more than a science.

 

[Diver300]

Well when I am looking at a circuit board, and trying to work out what is broken, I start by looking for component damage. This is sometimes physical damage, but often there is heat damage, in discoloured components or the board near the component. If the plastic packaging is distorted, that is a sure sign that the component is dead.

After that, it's a matter of trying to work out what the components do. There may be markings, and it is very common for one type of component to be used many times in one circuit. It's often useful to look on the internet for a circuit diagram of what I'm fixing. If that doesn't work, I'll draw out a circuit diagram for at least part of the circuit.

I often check the forward junction voltage drop on bipolar transistors, and that can often be done while they are in-circuit, as long as it is not powered. If the forward junction voltage drop is not in the range 0.4 - 0.7 V, the transistor is definitely broken, although for tests done in-circuit, there can be other current paths that show the voltage as being lower than it would be if the transistor were removed for testing.

Diodes can usually be checked the same way. LEDs will often light up when being tested, which is an absolute way of showing that they work.

I usually find it useful to check the resistance of resistors in-circuit. Although there are often other current paths that give a low reading, if the resistance is higher than the marked value, it is certainly blown. Also, it is rare for other current paths to give a reading many times lower than the marked value.

I hope this gives you some pointers.

 

[Dean Huster]

Smoked resistors are usually secondary failures caused by another component failing. A more modern example might be a charred bridge rectifier caused by a shorted filter capacitor. Antique radio restorers are always cautioned to "recap" an old radio, replacing ALL of the paper dielectric capacitors as they usually begin to get very leaky with age. A leaky paper coupling cap between a preamp and an output amp can cause the output tube to conduct with all its might, overheating and finally burining out the primary of the output transformer.