Single Drive XRFD Amplifier Troubleshooting

Overview

The water-cooled, single drive XRFD RF amplifier is installed on some MR450w systems. The MR450w system originally had an air-cooled SRFD2 single drive RF amplifier. Newer systems have the water-cooled single drive XRFD RF amplifier.

The solid-state, water-cooled, single drive XRFD RF amplifier accepts a single RF input from an independent digital exciter (DTX1) unit to produce the single drive body and single drive head RF outputs. The DTX signal input at RF amplifier J14 provides the RF drive for the body RF output when the amplifier is in body mode. It also provides the head RF output when the amplifier is in head mode. A single unblank signal input at RF amplifier J20 is used to control the body and head output ports. The body output channel port is capable of 16 kW peak envelope power at 63.86 MHz, while the head port is capable of 2 kW peak envelope power at 63.86 MHz.

The amplifier has a single step digital rotary encoder used for RF gain adjustment. In body mode, it is used to adjust gain that controls body RF output. In head mode, it is used to adjust gain that controls head RF output. Due to the fact that it is a digital device it must only be adjusted when the amplifier is actively pulsing RF. Adjusting it when the amplifier is idle will have no effect later when the amplifier is actively pulsing RF.

In normal operation, the driver module provides a separate body and head TR bias signal to the RF amplifier. The amplifier couples the corresponding bias signal onto the body and head transmit outputs.

Similar to the 3T single drive XRFD, this unit is equipped with monitoring sensors located in key areas of the amplifier to aid with service activities.

Table 1 XRFD Amplifier Sensor Locations
Callout on Functional Block Diagram	Connector Location	Sensor
1	J14	RF In Exciter sensor
2	J4	Body RF Out sensor
3	J3	Head RF Out Sensor
4	None	Signal Conditioner Gain
5	None	Mode Gain
6	None	PSU1 and PSU2 Low Voltages
7	None	PSU1 and PSU2 High Voltages
8	None	Cold Plate Temperatures

The RF amplifier communication interface is based on the CAN open protocol. This provides enhanced transfer of information to the system. The CAN link provides communication to/from the amplifier from the scan control processor (SCP). The amplifier I/F (AIF) board provides unblank control, emergency shutdown, and a rudimentary secondary control link to the dual drive RF amplifier.

Diagnostic RF, voltage, and temperature sensors are located in various sections of the RF amplifier. Diagnostic tools gather data from these sensors during scanning. This data can then be used to help assess the condition of the head and body transmit circuits as well as the general health of the RF amplifier. The RF amplifier is designed to be a single replaceable FRU. This XRFD RF amplifier does not contain any replaceable internal FRUs.

For replacement information about the XRFD amplifier, see 1.5T RF Amplifier Replacement.

Connector Layout

The XRFD amplifier has connectors labeled specifically for body and head operation. There are also communication connectors, A/C power connectors, and two coolant connectors. For more details, see Figure 4.

See the table below for the connectors for body transmit on the XRFD amplifier.

Table 2 Connectors for Body on XRFD Amplifier
Designator	Chassis Label	Description	Connector Type	Signal Type
J8	BODY SAMPLE A	Body forward RF power sample	BNC female	Low level RF
J6	BODY SAMPLE B	Body forward RF power sample	BNC female	Low level RF
J4	BODY RF OUT	Body RF power out	7/16 DIN female	High power RF with TR bias
J10	BODY TR	Body TR bias input	BNC female	Switching DC control

Connectors for Head

See the table below for the connectors for head on the XRFD amplifier.

Table 3 Connectors for Head on XRFD Amplifier
Designator	Chassis Label	Description	Connector Type	Signal Type
J3	HEAD RF OUT	Head RF power out	N female	High power RF with TR bias
J9	HEAD TR	Head TR bias input	BNC female	Switching DC control
J7	HEAD SAMPLE A	Head forward RF power sample	BNC female	Low level RF
J5	HEAD SAMPLE B	Head forward RF power sample	BNC female	Low level RF

Other Connectors

The illustration below shows J1, J2, J13, J14, J18, J19, and J20. The table below lists the connectors and their signal types.

Table 4 Other Connectors
Designator	Chassis Label	Description	Connector Type	Signal Type
J1	WATER IN	Supply water	Male QD	N/A
J2	WATER OUT	Return water	Male QD	N/A
J13	HSS/TEST	RF (HSS) test port output	BNC female	Low level RF (400 mW ∓10%) (26 ∓ 0.4 dBm)
J14	RF IN	RF input for Body and Head	BNC female	Low level RF (-4 to 4 dBm)
J18	CAN IN	CAN communication (input)	9-pin sub-D, female	Logic and 24 V
J19	CAN OUT	CAN communication (output)	9-pin sub-D, male	Logic and 24 V
J20	COMM	General communication (input)	25-pin sub-D, male	RS422
N/A	FACTORY PORT	Unused	9-pin sub-D, female	Unused

AC Line Power Input Connector

The AC line power TB1 input connector is a terminal block supporting 3-phase power provided by the power distribution unit (PDU). These power connectors are located on the upper left portion of the XRFD amplifier. There are three incoming lines (L1, L2, and L3) and a ground connector.

Circuit Breaker

The XRFD amplifier is protected by a circuit breaker.

LED Indicators

The XRFD RF amplifier has two parallel banks of 6 LEDs.

The LEDs in the top bank (from right to left) are labeled FLT, RFLK, OPER, WAIT, STBY, and OFF.

The LEDs in the bottom bank (from right to left) are labeled HEAD, BODY, TEST, UNBL, DCHV, and PWR.

Table 5
Chassis Label	Color	Description
OFF	Yellow	Module in power off state.
STBY	Green	Module in standby state.
WAIT	Yellow	Module in transient, processing state.
OPER	Green	Module in operate state.
RFLK	Yellow	Module RFLOCK signal active.
FLT	Orange	Module in fault condition.
PWR	Green	Module AC power is on.
DCHV	Green	High voltage power supply active.
UNBL	Yellow	Unblank signal present.
TEST	Green	Module in test mode.
BODY	Green	Module in body mode.
HEAD	Green	Module in head mode.

Troubleshooting Support

Diagnostic Capabilities

The XRFD amplifier contains several sensors that permit the monitoring of:

Internal PSU voltages
FET junction temperatures
Input and output peak and average RF power and VSWR for head and body RF output

These sensors are read by real-time system functions and diagnostic tools.

General Fault Isolation and Testing Process

Follow these general guidelines for troubleshooting XRFD amplifier issues:

From the Common Service Desktop, select Error Log > GE System Log to check for error messages regarding amplifier faults.
Read any extended error messages associated with the error fault (the error code number is highlighted in blue). Perform any recommended actions.
If necessary, execute one or more of the following tools or diagnostics:
- For XRFD amplifier communication problems, run CAN Link Diagnostic to confirm communication of all devices on the CAN Link, including the XRFD amplifier.
- For intermittent faults or those that only happen at a certain power level, run RF Power Check Tool .
- For image quality problems due to the following:,
  - Poor RF stability or fidelity: Run the RF Analysis (RFA) tool. This tool permits testing and isolation to each component in the transmit chain.
  - Coherent Noise: Poor shielding inside the XRFD can result in coherent noise on the head transmit port. Refer to the Coherent Noise Troubleshooting procedure and search the PSDB for XRFD and Noise for the latest information.
- To test the operation of the NB IF board in CAM and interconnection to XRFD amplifier, run RF Amp Interface Board Level Diagnostics.

Peripheral Hardware Reset

The system has a utility that allows you to start a hard-line reset to the amplifier if you think the microprocessors in the RF amp are locked up. This procedure is more aggressive than the CAN node reset executed by TPS. To access this utility from the Common Service Desktop, select the Utilities tab. In the Toolbox, select Peripheral Hardware Reset. Clear all check boxes except RF Amplifier Reset before running the utility.

Troubleshooting Hints

A poor RF load on the body or head RF transmit line can cause RF amplifier faults on a good, working RF amplifier. To prevent RF faults due to a bad RF load, connect the failing body or head RF output to a known good dummy load from the power measurement kit during testing. When using the 35kW dummy load, be sure to energize the dummy load fan.
The RF Amp Power Check Tool provides information about: output RF power, input RF power, unblank period, PSU voltage, and so on.
RF amplifier faults usually have an associated extended error message in the GE System Error log.
View XRFD PSU voltages in real time by typing mgd_term in a C-shell. Then in SCPWindow (at the prompt), type printVolts.
View XRFD PSU temperatures in real time by typing mgd_term in a C-shell. Then in SCPWindow (at the prompt), type printTemps.
View XRFD RF power in real time by typing Mgd_term in a C-shell. Then in SCPWindow (at the prompt), type printPower. The accuracy of the reported values depends heavily on the RF waveform in use and is inferior to that of the RF power measurement kit used during system calibration. Values reported by printPower are intended for troubleshooting purposes only. The RF waveform used by RF Amp Power Check Tool is designed to produce the best reported value results.