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| Illustration 1 | g01337095 |
Maintenance Bypass Cabinet Left Panel Components (1) Maintenance Bypass Cabinet Controller Board (2) Maintenance Bypass Cabinet Power Supply Board (MPS) (3) Time Delay Relay | |
The Maintenance Power Supply Board receives 21V power from the T11 transformer in the Maintenance Bypass Cabinet cabinet.
Refer to Systems Operation, Testing and Adjusting, RENR7654, "Transformer (Maintenance Bypass Cabinet)" for additional information about the T11 transformer.
These two unregulated power supply inputs are paralleled through diodes. These two unregulated power supply inputs prevent a failure of the filter capacitor in one power supply to cause a failure in the other supply.
The Maintenance Power Supply Board is used to supply control power to the Maintenance Bypass Control Board and to the Maintenance Bypass Cabinet Time Delay Relay.
The on-board power supplies have a dry contact (NC) output to indicate that the power supplies are OK. These outputs are in series so the OK signal is only good if both the 24Vdc and 12Vdc switcher is functional.
An additional function of the Maintenance Power Supply Board is to provide a hardware level of protection to prevent two specific failure modes that cannot rely solely on firmware for implementation.
The first fault condition is if both the Maintenance Bypass Cabinet and K5 breakers get closed at the same time and stay closed. The Maintenance Power Supply Board provides the fused power to a Time Delay relay that will be set to 4 seconds. If both breakers are closed for this amount of time this relay will time out and will provide a trip function to the K5 breaker thereby removing the fault condition.
The second fault condition is the prevention of back-feed during a transfer from Maintenance Bypass where the utility feed to the Maintenance Bypass Cabinet circuit breaker has been opened. In that condition, The Maintenance Power Supply Board prevents the Maintenance Bypass Cabinet Controller Board from closing the K5 breaker, which would cause the back-feed condition until the Maintenance Bypass Cabinet breaker has been opened. This fault condition is signaled to the Maintenance Bypass Cabinet Controller Board via dry contact closures so the proper machine state may be executed.
Fuses
Fuses, type, and function are indicated in Table 1. Visually inspect the fuses. Replace the fuse, if the fuse is blown.
| Maintenance Power Supply Board Fuses | ||
|---|---|---|
| Fuse | Specification | Protects |
| Maintenance Power Supply Board-F1 | 250VAC 10A | 24V Control Power |
| Maintenance Power Supply Board-F2 | 250VAC 3.15A Time Lag | Time Delay Relay Coil |
| Maintenance Power Supply Board-F3 | 250VAC 5A Time Lag | Time Delay Relay |
Maintenance Power Supply Board Diagram
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| Illustration 2 | g01273592 |
Removal
| NOTICE |
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Electrostatic discharge can damage integrated circuits or semiconductors if you touch bus connector pins. When not in use, keep the module in the static-shield bag. Follow these guidelines when you handle any module: Touch a grounded object to discharge static potential. Wear an approved wrist-strap grounding device. Do not touch the bus connector or connector pins. Do not touch circuit components inside the module. If available, use a static-safe work station. |
- Perform steps in the Systems Operation, Testing and Adjusting, "Internal Component Preremoval Steps (Maintenance Bypass Cabinet)" in order to de-energize the system and gain access to internal components.
- Disconnect all connectors from the board. The connectors locations in the unit are labeled. Verify each connector to make sure that the label is present and legible.
Refer to Illustration 2.
- Disconnect the eight white plastic standoffs connecting the board to the left panel using the following method.
Note: The board must be removed from the stand-offs without bending the board.
- Pinch the head of each stand-off so that the board is not locked to the stand-off but is still attached to the stand-off.
- Remove the board by gently and evenly pulling the board from all stand-offs at the same time.
Installation
| NOTICE |
|---|
Electrostatic discharge can damage integrated circuits or semiconductors if you touch bus connector pins. When not in use, keep the module in the static-shield bag. Follow these guidelines when you handle any module: Touch a grounded object to discharge static potential. Wear an approved wrist-strap grounding device. Do not touch the bus connector or connector pins. Do not touch circuit components inside the module. If available, use a static-safe work station. |
- Position the board in the cabinet over the eight white stand-offs that are connected to the left panel.
- Push the board, gently and evenly, onto all the stand-offs simultaneously. Make sure all stand-offs are locked in place.
- Plug the wire connectors into the correct connectors on the board. Check the labels on each connector for proper placement.
Refer to Illustration 2.