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Sect. IV Page 0
00010-2
Model 721A
SERVICING ITCHED CIRCUIT BOARDS
Excessive heat or pressure can lift the copper strip from the board. Avoid damage by using a low power
soldering iron (50 watts maximum) and following these instructions. Copper that lifts off the board should
be cemented in place with a quick drying acetate base cement having good electrical insulating properties.
A break in the copper should be repaired by soldering a short length of tinned copper wire across the break.
Use only high quality rosin core solder when repairing etched circuit boards. NEVER USE PASTE FLUX.
After soldering, clean off any excess flux and coat the repaired area with a high quality electrical varnish
or lacquer.
When replacing components with multiple mounting pins such as tube sockets, electrolytic capacitors, and
potentiometers, it will be necessary to lift each pin slightly, working around the components several times
until it is free.
WARNING:
If the specific instructions outlined in the steps below regarding etched circuit boards without
eyelets are not followed, extensive damage to the etched circuit board will result.
1. Apply heat sparingly to lead of component to be
replaced.
If lead of component passes through
an eyelet in the circuit board, apply heat on com¬
ponent side of board. If lead of component does
not pass through an eyelet, apply heat to con¬
ductor side of board.
3. Bend clean tinned leads on new part and care¬
fully insert through eyelets or holes in board.
2. Reheat solder in vacant eyelet and quickly in¬
sert a small awl to clean inside of hole. If hole
does not have an eyelet, insert awl or a #57
drill from conductor side of board.
4. Hold part against board (avoid overheating) and
solder leads. Apply heat to component leads on
correct side of board as explained in step 1.
In the event that either the circuit board has been damaged or the conventional method is impractical, use
method shown below. This is especially applicable for circuit boards without eyelets.
3
Clip lead as shown below.
2. Bend protruding leads upward.
Bend lead of
new component around protruding lead. Apply
solder using a pair of long nose pliers as a
heat sink.
This procedure is used in the field only as an alternate means of repair. It is not used within the factory.
Figure 4-1.
Servicing Etched Circuit Boards
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