The BSM-6000 platform: main units, input units, boards and the signal path

Identify which BSM-6301, 6501 or 6701 and which input unit is in front of you, name the boards that carry each parameter from the patient socket to the screen, and know where settings, review data and software live before you open anything.

Three main units, one architecture

The BSM-6301, BSM-6501 and BSM-6701 are one family that shares a service manual, an input unit range, a board set and a software structure. The difference you see first is the screen: the 6301 carries a 10.4-inch colour LCD, the 6501 a 12.1-inch and the 6701 a 15-inch panel, and the main units behind them are the MU-631R, MU-651R and MU-671R. The 6301 uses its own versions of the main digital board and the power unit; the 6501 and 6701 share theirs. Everything that touches the patient sits in a separate input unit that plugs into the left side of the main unit, and that split is the single most useful thing to understand about this monitor.

Each model exists in an A and a K variant, and the label on the main unit tells you which one you have. The manual does not explain the letters; it only marks what differs. Not for the A series: the ZS-900P telemetry transmitter, the TG-950P CO2 sensor kit and the AY-660P, AY-661P and AY-663P input units. Not for the K series: AF detection in the arrhythmia list. The Canadian CSA listing is quoted for the 6501A and 6701A only. Record the A/K letter as a configuration fact and check option compatibility against it before you order.

In mon-l1 you learned how a monitor measures and how to test it. This course does not repeat that. It adds what is specific to this platform: where each parameter is processed, which board owns which function, what the built-in diagnostic screens can prove, which parts are field-replaceable and which faults engineers actually meet.

Identify before you touch

Write down the main unit model and serial number, the input unit model and serial number, any smart expansion unit, optional interfaces, recorder, battery packs and the software versions. The software versions are shown on the information page of the system setup window and on the diagnostic check screen; some blocks, such as arrhythmia, NIBP and 12-lead analysis on the main board and the SpO2 program on the input unit, appear only on the information page. Record both views.

The input unit model decides more than the badge on the main unit does. It decides how many MULTI sockets you have, which SpO2 technology is inside and therefore which probes are compatible, and which boards you will order. Engineers who swap input units between beds without noting this end up chasing SpO2 'faults' that are simply the wrong probe family.

• AY-631P and AY-633P: SpO2 by a Masimo OEM unit; the 631 has one MULTI socket, the 633 three.
• AY-651P and AY-653P: SpO2 by a Nellcor OEM unit; one or three MULTI sockets.
• AY-671P and AY-673P, and likewise AY-661P and AY-663P: Nihon Kohden's own SpO2 board (UR-3908); one or three MULTI sockets.
• AY-660P: own SpO2 board, one TEMP socket and one MULTI socket that takes either IBP or CO2, and no ECG/BP analogue output socket.
• AA-672P and AA-674P smart expansion units: clip onto the input unit and add MULTI-socket parameters through their own processing board.
• A BSM-1700 series monitor can also act as the input unit; it has its own service manual.

Inside the main unit

The MAIN DIGITAL board is the heart of the main unit. It runs the host CPU and the system software, holds the flash memory with the program, the FRAM with the settings, the SDRAM, the internal SD card for review data, the real-time clock with its lithium backup cell, the LVDS output to the LCD, the network interface and the audio. The manual also gives it the job of supplying power to the rest of the monitor, and the battery charging circuit is on it too. When the troubleshooting tables end in 'replace the MAIN DIGITAL board', this is why: very little in the main unit works around it.

Around it sit the smaller boards. The FRONT I/F board carries the remote control receiver and the touch screen controller and relays signals between the front panel and the main board. The front mother board set combines the power switch, operation keys, alarm indicator and record key boards and is replaced as one set. The touch panel interface board connects the touch screen. The INPUT I/F board is the link to the input unit: it passes supply voltages, the input detection line and serial communication. Two battery mother boards hold the two battery slots. The power unit, mounted on a heat sink block, converts mains to the internal supplies; on the larger main units it has a discharge switch that matters in lesson 5. The LCD has its own backlight inverter, LVDS cable and touch screen.

The batteries in this manual are SB-671P packs, nickel-metal hydride, up to two of them in slots on the sides of the main unit. The manual gives a nominal 9.6 V, a life of about one year or 200 full cycles, and a run time with new, fully charged packs of about 90 minutes on the 6301 and 6501 and about 60 minutes on the 6701. Separately, the main board carries a lithium coin cell for the clock and memory backup. Check the label of every pack you meet: if you find a different chemistry, follow the documentation for that pack, not this paragraph.

Inside the input unit

The input unit is a self-contained measurement front end with its own processors. The ECG connector board takes the lead wires and carries the defibrillation protection resistors; the ECG RESP board behind it amplifies ECG and runs the impedance respiration carrier, and its processor is the block shown as EPU in the software list. The MPU board, which sits inside the NIBP unit assembly, processes NIBP, IBP, temperature, thermistor respiration, cardiac output and FiO2 and talks to the SpO2 and CO2 modules; its program is DPU0. The TEMP board carries the dedicated temperature sockets and passes power and serial lines to the MPU. The MPU PWR board generates the isolated floating supply for the measurement side and hosts the SpO2 interface. The AY MOTHER board ties it all to the main unit connector and also contains the drive and power switching for the NIBP pump and valves.

The NIBP unit, SG-670P, SG-671P or SG-673P depending on the input unit, contains the MPU board, a small rolling pump, the solenoid valves and the internal tubing with a filter, a check valve and joints. The MPU board carries two separate pressure sensors: one for measurement, whose gain and offset are set at the factory and stored on the board, and one that feeds an independent safety monitor. That safety monitor cuts power to the pump and valves and dumps the cuff if pressure goes too high or stays up too long. You will test it in lesson 2, and it is the reason a NIBP accuracy fault on this platform ends in a part replacement, not a user adjustment.

In the smart expansion unit the EXTMPU board does the same work as the MPU for the extra MULTI sockets, with its own program, DPU1.

The signal path, socket to screen

Follow one parameter at a time. ECG enters at the ECG/RESP socket, passes the protection network on the connector board and is amplified and digitised on the ECG RESP board. SpO2 enters at the SpO2 socket and goes to the OEM unit or the UR-3908 board through the MPU PWR board. A MULTI socket identifies the cord plugged into it and routes IBP, temperature, cardiac output, thermistor respiration, FiO2, CO2 or BIS to the MPU or EXTMPU processing. The NIBP socket detects whether an adult or neonatal hose is connected and sets the mode accordingly. All of these results travel as serial data through the AY MOTHER board, the input unit connector, the INPUT I/F board and its cable to the MAIN DIGITAL board, which draws them, runs the alarms and sends them to the network.

This path gives you the split-half test you will use all through lesson 4. A problem that follows the accessory is the accessory. A problem that stays with one socket but clears on another MULTI socket is in that channel of the MPU or EXTMPU. A problem that stays when the input unit is moved to a known-good main unit is in the input unit; one that moves away is in the main unit, its INPUT I/F board, or the cable between them.

Patient protection is built into the input side. The manual classifies the ECG, respiration, IBP, temperature, SpO2, CO2, O2, NIBP and BIS inputs as defibrillation-proof type CF applied parts, and gives the ECG and impedance respiration inputs protection against a 400 J defibrillator discharge. Cardiac output on a MULTI socket is type CF but not defibrillation-proof, and the manual warns against touching the CO cord during defibrillation. The ECG/BP OUT socket supplies analogue ECG, IBP and a heart-rate trigger for synchronising other equipment; the manual allows only its own defibrillators to use that trigger for synchronised discharge.

Network, options and where data lives

The monitor connects to the central station through the network socket on the side of the main unit. The manual requires that connection to go through a LAN isolation unit and that every network job is agreed with, and done under the direction of, the hospital's network administrator. Optional rear interfaces add multi-link ports for external devices, nurse call, USB for a mouse or barcode reader, RS-232C and a video output for a slave display; the QI-670P adds a Bluetooth module. The interfaces themselves are replaced as units.

Before any service work, know where things are stored. Settings live in the FRAM on the MAIN DIGITAL board. Review data, meaning trends, alarm history, full-disclosure waveforms and arrhythmia recall, lives on the internal SD card. Replacing the MAIN DIGITAL board loses everything; replacing the internal SD card loses review data; replacing the lithium cell loses review data and the clock. Settings can be backed up to the internal SD card or to an optional SD card and loaded back, but only between the same model and the same software version. That is lesson 5 in detail; for now, remember that the first thing you do on this monitor is find out what you are about to lose.

There is one more trap. With SHOW ADMIT CONFIRMATION WINDOW off in the system configuration, the monitor erases the admitted patient and the measurement data, and resets settings, half an hour after it is switched off. When data transport using the input unit is enabled, that setting is forced off. In a maintenance job where the data must survive, check both settings with the ward first.

On-site checklist

• Main unit model, A/K variant and serial number recorded
• Input unit and smart expansion unit models and serial numbers recorded
• Software versions read on the system setup information page and the diagnostic check screen
• Optional interfaces, recorder and number and type of battery packs noted
• SpO2 technology of the input unit identified and probe family checked
• Network connection checked to run through the LAN isolation unit; network administrator known
• Automatic data erase setting checked before any power-off during service

Check yourself