Check, Add Resistors On Optimod-Fm Card #Ps - Orban 8100A/XT2 Operating Manual

Installation
2-7
2) Check, add resistors on PTIM D-FM Card #PS.
Allow about 45 minutes for this step.
a) Check the values of resistors R103 and R104 on the OPTIMOD-FM Card #PS, the
power supply regulator card. If the values of R103 and R104 are already 0.62 ohms
(blue-red-gold-gold), or if " piggyback " resistors of 1.8 ohms (brown-gray-silver) have
been added in parallel to existing 0.91 -ohm resistors, skip to step d.
Card #PS is mounted on the inside of the rear panel. These large resistors can be seen
by opening the front panel, removing the subpanel, then looking in the rear interior of
the unit to the left of Card #3. A flashlight will be necessary.
b) Remove the OPTIMOD-FM from the rack, place it on a bench, and carefully open the
rear panel.
Set the unit on a pad with the rear panel facing you and about 6 " (15cm) back from
the edge of the bench. Make certain the power cord is unplugged. Remove the screws
which attach the top and bottom covers to the rear panel (eight screws on each cover).
There is no need to remove the other cover screws. Remove the nine screws circled in
black on the rear panel. Very carefully and slowly pull the rear panel out about 3/4 "
(2cm), then tilt the top edge down until the rear panel is horizontal.
CAUTION
Watch for snags in the internal wiring and for any stress on
the ceramic capacitors on the divider wall or input filter box.
These capacitors are very fragile and difficult to replace.
c) Connect a 1.8-ohm resistor in parallel with R103. Connect another 1.8-ohm resistor
in parallel with R104.
Two 1.8-ohm (brown-gray-silver-silver or brown-gray-silver-gold), 1-watt wirewound
resistors are supplied with the XT2. Bend each lead at right angles (about 1/8 " from
the resistor bodies), then " piggyback " the new resistors onto the old on the component
side of the board. To avoid heat damage, solder the leads together as far away from the
resistor bodies as practical. We suggest you mark these changes on the power supply
schematic. The net value of each resistor pair is now approximately 0.62 ohms.
d) If your OPTIMOD-FM is a Model 8100A (with a serial number below 638000),
skip to step 3.
If you have a Model 8100A/1 (serial number 638000 or above), close the rear panel
(but not the front panel) if open, remount the unit in the rack, skip the rest of the
RETROFIT INSTRUCTIONS, and follow the INSTALLATION INSTRUCTIONS on
page 2-3.
When replacing the rear panel, make sure that no wires are pinched under the flanges.