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Product Number: MAS-28M= and MAS-28C=
The replacement part for this procedure is the MAS-28 175 watt power supply, and is recommended for use in M and C chassis currently equipped with the MAS-28 power supply. You must determine the power supply you have and use the appropriate documentation for that power supply.
 | Caution This procedure is recommended only for experienced technicians and engineers because access to the chassis interior is required. Before beginning this procedure, it is strongly advised that you read through the entire document. If you have any doubts about your ability to perform any part of this procedure, contact a service representative for further guidance. |
 | Warning Before accessing to the chassis interior, turn off power to the chassis and unplug the power cord. Use extreme caution around the chassis since potentially harmful voltages are present. |
The MAS-28 will operate with either 110 volt or 220 volt alternating current (AC) source input (auto-ranging) and provides direct current (DC) output voltages of ± 5 volts and ± 12 volts.
Note: The kit you received includes the MAS-28, a new switch assembly, and assorted components and hardware. For this procedure, you will use only the MAS-28 power supply and mounting plate. The other accessories in the kit are not used for this replacement procedure.
Electrostatic discharge damage (ESD) occurs when electronic printed circuit cards are improperly handled and can result in complete or intermittent failures. ESD can impair electronic circuitry and equipment. Always follow ESD prevention procedures when removing and replacing cards.
Following are steps for handling printed circuit cards:
Step 2: Connect the strap to an unpainted chassis frame surface or another proper grounding point or surface to safely channel unwanted ESD voltages to ground (see Figure 1).
Step 3: Use the ejectors to remove the card. Handle the card by its sides. Place the card on an antistatic surface or in a static shielding bag. To prevent further damage to the card by ESD voltages, defective cards must remain in the static shielding bag when returned for repair or replacement.
Step 4: Handling the new card by its edges only, insert it into the chassis. Avoid contact between the card and clothing. The wrist strap only protects the card from ESD voltages on the body; ESD voltages on clothing can still damage the card.
Use an ohmmeter to check the ESD wrist strap to ensure that the resistor is providing proper ESD protection. For safety, the measurement should be in the range of 1 to 10 Mohms.
Refer to the following procedures and accompanying illustrations to access and remove the suspect power supply and to install the new MAS-28 power supply. Before you start any procedures, read through this entire document to familiarize yourself with the required tasks.
 | Warning Before accessing the chassis interior and removing any cards, turn off power to the chassis and unplug the power cord. High voltages may exist in or near the power supply. Use extreme caution when working with the power supply. Attach appropriate ESD protection before beginning this procedure. |
Once you have taken the necessary ESD precautions, you can proceed with the installation of the new MAS-28 power supply.
The following items are required for installation of the MAS-28 power supply:
n Two Phillips screwdrivers: No.1 and No. 2
n One medium flat-blade screwdriver
n One pair of medium needle nose pliers
n Digital Multimeter (DMM) or Digital Voltmeter (DVM)
Note: The following procedures differ for M and C chassis; refer to the appropriate section depending upon your chassis type.
Following is the procedure for accessing the M chassis:
Step 2: Locate the three screws that secure the card cage access panel. Use the flat-blade screwdriver to turn each of these screws 1/4 to 1/2 turn counterclockwise until the screws pop up.
Step 3: Loosen the three screws at the bottom edge of the card cage cover (do not remove these screws completely). Carefully remove the cover and set it aside.
Step 4: Orient the chassis so that the back (the side with the ports) is to your left; the front of the chassis (the side with the LED) is to your right; and the card cage opening is on the side of the chassis facing away from you. This will place the power supply on the side of the chassis closest to you. Looking straight down at the power supply, the position of the terminal strips and wires attached to them should resemble the wiring diagram in Figure 4.
Proceed to "Removing the Suspect Power Supply."
Following is the procedure for accessing the C chassis:
Step 2: Orient the chassis so that the back (the side with the ports) is on your left, and the front (with the LED) of the chassis is on your right. This will place the power supply on the side of the chassis closest to you after you remove the cover.
Step 3: Pull the front of the cover to the right while securing the back of the chassis with your left hand. Pull slowly and carefully; the fit is snug.
 | Caution Several cables are located close to the interior of the C chassis cover. Avoid damage to these cables by ensuring that they do not impede the cover as you remove it. |
Step 4: Pull the cover to the right until the power supply and the card cage are completely exposed, but do not pull the cover completely off.
Step 5: Looking straight down at the power supply, the position of the terminal strips will resemble the wiring diagram in Figure 4.
Proceed to "Removing the Suspect Power Supply."
Following is the procedure for removing the suspect power supply from both the M and C chassis:
Step 2: Loosen (but do not remove) all of the screws on TB2 (to which wires are attached).
Step 3: Once loosened, pull the wires from beneath the screws.
Step 4: Loosen (but do not remove) all three screws on TB1.
Step 5: Once loosened, pull the wires from beneath the screws.
Step 6: Locate the Phillips screws securing the power supply mounting plate to the chassis base (see Figure 4.
Note: In the M chassis, five screws are used for the mounting plate. In the C chassis, four screws are used (the lower right screw hole in Figure 4 is not used in the C chassis).
Step 7: Remove the screws from the power supply mounting plate.
Step 8: Lift the suspect power supply (and plate) out of the chassis and set it aside.
Proceed to "Installing the New Power Supply."
Following is the procedure for installing the new MAS-28 power supply in both the M and C chassis:
Step 2: Remove the new power supply (with the attached mounting plate) from its packaging.
Step 3: Loosen all of the screws on terminal strips TB1 and TB2 (to which wires will be attached).
Step 4: Place the new power supply in the chassis. Refer to Figure 4 for correct positioning.
Step 5: Use the No. 2 Phillips screwdriver to install the screws that secure the power supply mounting plate (attached to the MAS-28) to the chassis base.
Note: In the M chassis, four screws are used for the mounting plate. In the C chassis, three screws are used (the lower left screw hole in Figure 4 is not used in the C chassis).
Step 6: Locate the red and black wires from the backplane; there are four of each color. Two of each of these colors are shorter than the other two.
Step 7: Group the two short red wires together and then group the two long red wires.
Step 8: Group the two short black wires together.
Note: These three wire pairs will be attached to specific terminal positions in the following steps.
Step 9: Starting with terminal position TB2-1, attach the wires to TB2 (follow the wiring diagram in Figure 4). Make certain to attach the wire-pairs to TB2-7 through TB2-9 (see Table 1).
Table 1 Connections to Terminal TB2
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Step 10: Attach the long chassis ground wire (green with yellow stripes) to TB2-5.
Step 11: When all wires are secure, double check the color-coding for the wires in Figure 4 and Table 1.
Step 12: Following the wiring diagram in Figure 4, attach and secure the three wires (brown, blue and green with yellow stripes) to TB1 starting with TB1-1 (Line, brown wire).
 | Caution When all wires are secure, double check the color-coding in Figure 4. |
Proceed to "Testing the New MAS-28 Power Supply."
After you install the new MAS-28 power supply in your chassis, you can test the installation by measuring the voltages on the new power supply. Testing will first be done with all cards removed from the chassis, and then with one card installed in the chassis. Testing with all cards removed will prevent damage caused by improper power supply wiring. This procedure requires the DVM set for DC-voltage operation.
 | Warning High voltages may exist in or near the power supply; use extreme caution when working with the power supply. Connect all ESD protection at this time. |
Following is the procedure for testing the new power supply in the M and C chassis.
Step 2: C chassis only—Locate the two clamps that hold the printed circuit cards in place in the card cage (see Figure 5) and use the flat-blade screwdriver to loosen the screws on the two clamps. Remove these clamps and set them aside.
Step 3: Locate the edge ejectors on the cards inside the card cage. Partially remove all cards so that they make no electrical contact with the backplane. Do not remove the cards completely from the card cage. Follow the card removal procedures described earlier (see Figure 6).
 | Caution To avoid overheating the chassis during the following steps, apply power to the chassis only long enough to check the fan operation. |
Step 4: Plug in the power cord and turn on power to the chassis. You are operating the power supply with no cards installed to protect them from damage due to an improperly wired power supply.
Step 5: Observe that the chassis fan(s) is (are) operating, which will indicate that the + 12 volt power supply is operational. Also check that the LED on the front panel of the chassis is on, indicating that the +5 volt power supply is operational.
Note: If the front-panel LED flickers, this is a typical condition with no load applied and does not indicate a failure in the power supply.
Step 6: Turn off power to the chassis and unplug the power cord.
Step 7: Re-insert only the processor card (in the top chassis slot) making certain it is properly seated. This card will provide a load to the power supply.
 | Caution To avoid overheating the chassis during the following steps, apply power to the chassis only long enough to check the power supply voltages. |
Step 8: Plug in the power cord and turn on power to the chassis.
 | Warning To avoid a short circuit and electrical shock hazard, exercise great care with the DVM probes. Do not touch more than one wire with one probe. A short circuit could cause damage to all cards and the power supply. |
Step 9: Referring to Figure 7, locate position 1 at the far left of the backplane (black wire). Touch this ground reference point with the black probe of the DVM and maintain contact through the following step.
Step 10: Touch the red probe to each wire position (positions 2 through 9), exercising extreme caution, and compare the voltage measurements with those listed in Table 2. If the measured values fall outside the range given in Table 2, confirm your wiring connections and recheck your voltages.
Table 2 Voltage Ranges for Backplane Test Points (TP)
If all measured voltage values are within the specified ranges, turn of the power, disconnect the power cable, and proceed as follows:
n M chassis only—Re-insert all remaining cards and replace the top cover and the card cage cover on the side of the chassis using all removed screws (see Figure 2).
n C chassis only—Re-insert the remaining card, reattach the card clamps at either end of the card cage, and replace the top chassis cover using all removed screws (see Figure 3).
The system is ready to be installed in the network.
If any measured voltage values are not within the specified ranges, check problematic power supply connections and repeat the tests.
If, after repeating the tests, measured voltage values are outside the specified ranges, immediately turn off power to the chassis and contact your service representative for further guidance
Posted: Thu Nov 6 16:18:36 PST 2003
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