of plating, or the board itself, is broken, it can be repaired as
shown in figure 5-1. The printed wiring is covered with a fungus
proof coating, therefore, the coating should be removed in the area
to be repaired before soldering.
SERVICING TRANSISTORIZED EQUIPMENT.
ized circuitry is similar to servicing equivalent vacuum tube circuitry.
some special techniques must be acquired before servicing
Some of these are listed below.
(1) When using battery eliminator bench type power supplies,
The output of the
the ripple voltage should be held to a minimum.
supply should be well regulated to prevent exceeding the safe poten-
The proper polarity must
tial limits under varying load conditions.
be observed to prevent damage to transistors.
(2) When transistor replacement is required, avoid over-
Excessive heat from the
heating the transistor while soldering.
soldering iron can also damage other transistors close by.
replacing diodes or transistors, use a small soldering iron (25 to
With a pair of long nose pliers, hold the lead between
the part and the soldering iron.
new transistor, check for circuit defects which may damage
the new transistor.
20,000 ohms per volt, or better, on all voltage ranges.
a lower sensitivity draw too much current from the circuits and
cause inaccuracies; in addition, high current may damage the
(4) Soldering guns or irons of the heavy duty type should
A check for current leakage should be made on all
never be used.
soldering irons used, or they should be operated from an isolation