Table of Contents
Advertisement
PAC HANDLING AND REPAIR PROCEDURES
Inserting and Removing System PACs
CAUTION
Turn off de power before inserting or removing
circuit cards.
Failure to turn off the power might
damage the PAC.
a.
Insert µ,-PAC modules by engaging theµ -PAC in the appropriate slot of the
µ-BLOC and pressing the µ-PAC into position until the connector engages and sets.
The
µ-PAC module is inserted with components on the bottom.
b.
Remove µ-PAC modules from µ-BLOCs by engaging the two holes at the handle
end of the µ-PAC with the µ-PAC extractor tool.
A 20-lb force is sufficient to disengage any
µ-PAC from its mating connector.
The µ-PAC can then be removed with the fingers.
PAC Troubleshooting
The Extender PAC, Model XP-330 permits access to points on the PACs.
Signals
on the pins of the PACs may be ascertained from the PAC descriptions.
Leads for observing
current waveforems using an ac current probe are provided on special extender PACs.
Component Checking
Many PACs have several identical channels.
In most cases components can be
checked by resistance comparison with parts on other channels or other PAC s.
a.
Transistor Checking.
Transistors on a PAC can be checked with an ohmmeter.
Do this carefully to avoid damaging the transistors by large meter currents.
Check the
base-emitter and collector -emitter junctions in both directions, using the meter scale which
will apply the least amount of current to the transistor and still provide a reading.
Replace
any transistors having open or shorted junctions, or whose resistance readings differ con-
siderably from those obtained on a transistor on an identical channel or PAC.
b.
Diode Checking.
Check diodes by comparing their forward and back resistances
with diodes of the same type on other channels or PACs.
c.
Resistors and Capacfrors.
Free one end of the resistor and check its resistance
by using an ohmmeter in the conventional manner.
To check most small capacitors for open
circuits, a vacuum-tube ohmmeter is needed to induce a needle "kick."
Component Replacement
a.
Use only top quality rosin-core 60/40 solder (60% tin, 40% lead).
b.
Use a small hot soldering iron.
Use a heat sink on the lead of the component,
in the form of a pair of pliers or an alligator clip, to conduct heat away from the body of
the component while soldering.
c.
Remove excess solder from the etched side of the printed circuit board.
Use a
piece of large-diameter spaghetti or a commercially available tool for removing excess
solder from eyelets.
3-2
Advertisement
Table of Contents
