8 QSC Audio Products, LLC
TD-000163-00 Rev. B
Solder braid
Solder
Solder
Tweezers
Solder
1.4 Working with surface-mount components
ISA amplifiers, like many modern electronic products, use surface-mount technology (SMT) components where appropriate in order to
make high-density circuitry that is reliable and economical to manufacture.
SMT components in the ISA amps are used in the small-signal and control circuits, so they do not handle significant amounts of power;
therefore, they are subject to very little stress and should seldom fail. Sometimes they do fail, or they require replacement for a
performance upgrade or modification. Thus, it is important to know how to work with SMT components.
Specialized tools and equipment exist for soldering, unsoldering, and removing SMT components quickly and efficiently, but they are often
expensive. Most SMT repairs, though, can be handled reasonably well with common tools and equipment, such as tweezers, solder braid, and
fine-tip soldering irons. The original factory components are tacked to the board with a spot of glue, so you might have to apply some force
to break the adhesive.
Two-terminal components (resistors, capacitors, diodes, etc.)
Removal
1 Use two soldering irons, preferably about 25 to 40 watts, with fine tips.
2 With a soldering iron in each hand, hold one tip on the solder at one end of the component and the other
tip on the other end (Figure 1.1).
3 Once the solder melts on both ends, grip the component between the two tips and lift it from the circuit
board.
4 Use solder braid and a soldering iron to remove the solder from the two pads (Figure 1.2).
Insertion
1 With a soldering iron and appropriate solder, melt just enough solder onto one pad to create a small
mound (Figure 1.3).
2 Grasp the component in the middle with tweezers. Melt the small mound of solder with the iron and
place the component across the two pads (in the correct orientation, if the component is sensitive to
direction) and press it flat against the circuit board, with one end of the component immersed in the
melted solder (Figure 1.4).
3 Hold the component in place and take the soldering iron away. Let the solder harden to tack the component in place.
4 Fully solder the other end of the component to its pad. Let the solder harden (Figure 1.5).
5 Fully solder the tacked end of the component to its pad (Figure 1.6).
Three-terminal components (transistors, etc.)
Removal
1 With a soldering iron and solder braid, remove as much solder as possible from the middle terminal of
the component.
2 With a soldering iron in each hand, hold one tip on the solder at the terminal at one end of the compo-
nent and the other tip on the terminal at the other end.
3 When the solder on both ends melts, grip the component between the two tips and lift it from the circuit
board. You might need to quickly touch the pad on the middle terminal with a soldering iron to melt any
remaining solder that might be holding the component down.
4 Use solder braid and a soldering iron to remove the solder from the three pads.
Insertion
1 With a soldering iron and appropriate solder, melt just enough solder onto one pad to create a small
mound of solder.
2 Grasp the component with tweezers. Melt the small mound of solder with the iron and place the
component in the correct orientation across the three pads and press it flat against the circuit board,
with one terminal of the component pressed into the melted solder.
3 Hold the component in place and take the soldering iron away. Let the solder harden to tack the
component in place.
4 Fully solder the other terminals of the component to their pads. Let the solder harden.
5 Fully solder the tacked terminal of the component to its pad.
Figure 1.1.
Figure 1.2.
Figure 1.3.
Figure 1.4.
Figure 1.5.
Figure 1.6.
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