Service Preliminaries - Lexicon Prime Time 93 Owner's Manual

Refit the cover and the cord. Power up. If the unit still does not power up
or if a fuse blows once again, refer the problem to an authorized service
technician or return the unit to Lexicon.
5.2 SERVICE PRELIMINARIES
If the field service is attempted, first verify the operation of all power
supplies. A convenient place to probe power supplies is at their
chassi~­
mounted three-pin regulators, U68, U69, and U70. Their corresponding volt-
ages are printed on the circuit board near the appropriate leads. Use the
chassis as a ground reference and take care when probing that the probe does
not short adjacent leads of the regulators. See FIG. 5.0 to identify these
test points. The following table indicates appropriate voltage limits:
LIMITS
REGULATOR VOLTAGE MIN. MAX.
U68 +5V 4.75V 5.25V
U69 +15V 14.25V 15.75V
U70
-15V
-14.25V -15.75V
NOTE: If both memory and analog subsystem modules are removed from the mother-
board, the analog (±15V) ground and the digital (+5V) ground become
isolated. This means that correct voltage readings are obtained only
when measuring with respect to the corresponding ground. Do not remove
modules under power.
Should module removal be required proceed as follows:
Each module is held in place by four nylon standoff retainers. Each retainer
has a small locking barb which must be depressed with needle nose pliers or
screwdriver while carefully lifting the circuit board at the nearest corner.
Release one corner at a time and then lift the entire module from the mother-
board.
Installation of circuit boards require alignment of all connector pins with
their mating receptacles. After positioning board, firmly press each corner
until all lockin,g barbs are engaged.
57