Hi, I've just joined AAC and this is my first post.

I'm currently attempting to reverse engineer a circuit board in order to create a circuit diagram. On the PCB there are many standard components I recognize but also many miniature ones that I have no experience of. I would therefore appreciate if someone could clarify why they are used along side standard size components, and also how to correctly identify:-
a, What they are (resister, capacitor or diode)?
b, What their values are?
c, Polarity?

Using a magnifying glass and checking across the connections with an Ohmmeter, the values on the black components in the pictures tie up with their metered values, albeit they are still in circuit and therefore might be influenced by other components. But mainly why these tiny components are used in the first place and where I could read the why's and therefore's on them?

Many thanks

 

Welcome to AAC!

The black two terminal devices all look like resistors. With 3 digits, they conform to the E24 series labeling: 2 significant digits and a multiplier. 103 would be 10k.

The black three terminal devices could be transistors or diodes. You can find a SMD code listing to try to determine standard part numbers.

The two terminal yellow devices are tantalum capacitors. Value will be specified in pF, 2 significant digits and a multiplier.

Two terminal blue likely a resistor with 3 significant digits and a multiplier.

Can't see the Mini-MELF component clearly enough to guess. Most likely a diode.

 

The black devices with numbers on them are resistors. They are read the same way as color coded resistors. That is, 2 or three digits followed by a multiplier.

The tan colored units are tantalum capacitors. The black stripe is the positive end.

The three-leaded parts are transistors or diodes. The transistors can be either bipolar or FET's.

What appears to be a round, glass device is probably a diode. Going by its small size I would guess that it is a signal diode similar to a 1N4148. I could also be a Zener diode.


Why are these small parts used? Because they are small. Also, because they cost a lot less to make and install.

Because of their small size, they use less material than larger parts. Unlike through-hole components, these parts do not need any preparation such as bending and cutting of the leads. These components are put on the PCB by robots and soldered in a reflow oven -- There is very little hand labor involved. The printed circuit board requires fewer plated through holes so they are cheaper and more reliable.


@dl324 beat me to most of this.

 

Dennis

Many thanks for your quick response.

I've found an SMD code book online so I'll check that out to see if I can make sense of it. In the meantime could you please explain why these under board componetns are used instead of the regular sized ones? Is it PCB space or some other reason?

Thanks and best regards

 

The black devices with numbers on them are resistors. They are read the same way as color coded resistors. That is, 2 or three digits followed by a multiplier.

The tan colored units are tantalum capacitors. The black stripe is the positive end.

The three-leaded parts are transistors or diodes. The transistors can be either bipolar or FET's.

What appears to be a round, glass device is probably a diode. Going by its small size I would guess that it is a signal diode similar to a 1N4148. I could also be a Zener diode.


Why are these small parts used? Because they are small. Also, because they cost a lot less to make and install.

Because of their small size, they use less material than larger parts. Unlike through-hole components, these parts do not need any preparation such as bending and cutting of the leads. These components are put on the PCB by robots and soldered in a reflow oven -- There is very little hand labor involved. The printed circuit board requires fewer plated through holes so they are cheaper and more reliable.


@dl324 beat me to most of this.

Thank you Richard0, a precise response that has answered my question.

Many thanks