Tektronix 2445, Instruction Manual

Page: 158 / 351

Maintenance— 2445 Service
layers. If any inner-layer conductive path becomes broken
due to poor soldering practices, the board becomes unus­
able and must be replaced. Damage of this nature can void
the instrument warranty.
> C A U T I O N <
Only an experienced m aintenance person, pro ficien t in
the use o f vacuum -type desoldering equipm ent should
attem p t rep air o f an y circuit b o ard in this instrum ent.
Excessive h e a t can cause the etch ed circuit conduc­
tors to sep arate from the circuit board. N ever allo w
the so ld er e x tra cto r tip to rem ain a t one p lace on the
b o ard fo r m ore than three seconds. S o ld er wick,
sprin g -actu ated o r squeeze-bulb so ld er suckers, an d
h e a t blocks (fo r desoldering m ultipin com ponents)
m u st n o t be used. D am age cau sed b y p o o r soldering
techniques can void the instrum ent w arranty.
Desoldering parts from multilayer circuit boards is espe­
cially critical. Many integrated circuits are static sensitive
and may be damaged by solder extractors that generate
static charges. Perform work involving static-sensitive de­
vices only at a static-free work station while wearing a
grounded antistatic wrist strap. Use only an antistatic vacu­
um-type solder extractor approved by a Tektronix Service
Center.
> C A U T I O N <
A ttem p ts to unsolder, rem ove, an d reso ld er leads
from the com ponent side o f a circuit b o ard m ay cause
dam age to the reverse side o f the circuit board.
The following techniques should be used to replace a
component on a circuit board:
1. Touch the vacuum desoldering tool to the lead at the
solder connection. Never place the iron directly on the
board; doing so may damage the board.
N O T E
Som e com ponents are difficult to rem ove from the cir­
cuit board due to a bend p laced in the com ponent
leads during m achine insertion. To m ake rem oval o f
m achine-inserted com ponents easier, straighten the
com ponent leads on the reverse side o f the circuit
board.
2. When removing a multipin component, especially an
1C, do not heat adjacent pins consecutively. Apply heat to
the pins at alternate sides and ends of the 1C as solder is
removed. Allow a moment for the circuit board to cool be­
fore proceeding to the next pin.
3. Bend the leads of the replacement component to fit
the holes in the circuit board. If the component is replaced
while the board is installed in the instrument, cut the leads
so they protrude only a small amount through the reverse
side of the circuit board. Excess lead length may cause
shorting to other conductive parts.
4. Insert the leads into the holes of the board so that the
replacement component is positioned the same as the origi­
nal component. Most components should be firmly seated
against the circuit board.
5. Touch the soldering iron to the connection and apply
enough solder to make a firm solder joint. Do not move the
component while the solder hardens.
6. Cut off any excess lead protruding through the circuit
board (if not clipped to the correct length in step 3).
7. Clean the area around the solder connection with an
approved flux-removing solvent. Be careful not to remove
any of the printed information from the circuit board.
8. When soldering to the ceramic crt-termination net­
work, a slightly larger soldering iron can be used. It is rec­
ommended that a solder containing about 3% silver be used
when soldering to the ceramic material to avoid destroying
the the bond. The bond can be broken by repeated use of
ordinary tin-lead solder or by the application of too much
heat; however, occasional use of ordinary solder will not
break the bond, provided excessive heat is not applied
when making the connection.
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