Alarm 926 (FSSB ALARM)

Causes and actions

A fault occurred on the FSSB (serial servo bus) that connects servo amplifiers to the CNC.

This alarm is issued if a fault occurs in any of the axis control cards making up the FSSB, optical cables, and servo amplifiers.

•  Identifying the defective location

Use the LEDs on the servo amplifiers.

Using the 7–segment LEDs installed on the servo amplifiers, the defective location can be identified.

FSSB connection example

If portion A, indicated by dotted line, contains the defective location, the LEDs on the servo amplifiers will be as shown in the table below.

In this case, any of the following locations may be defective:

1. Optical cable connecting together the servo amplifier whose LED is “L” or “–” and that whose LED is “U”. In the above figure, the optical cable in portion A may be
2. Either of the servo amplifier whose LED is “L” or “–” and that whose LED is “U”. In the above figure, either amplifier 2 or 3 may be defective.

If portion B, indicated by dotted line, contains the defective location, the LEDs on the servo amplifiers will be as follows:

In this case, any of the following locations may be defective:

1. Optical cable connected to the In the above figure, the optical cable in portion B may be defective.
2. Any of the axis control cards in the CNC
3. First servo amplifier In the above figure, amplifier 0 may be defective.

•Identifying the defective location

Use the display on the CNC screen

If alarm 926 is issued, information such as the following is displayed at the bottom of the CNC screen. It can be used to identify the defective location.

Bits 12 to 15 of the MODE information indicate the number of the slave in which the alarm occurred. The unit nearest the CNC (such as a servo amplifier) is assigned a slave number of “0”. For a 2–axis amplifier, for example, one number is assigned for the first axis, and the next number is assigned for the second.

Details of the MODE information

Using the bits of the STATUS information, the fault can be estimated.
Details of the STATUS information

If the pattern of the STATUS information is A

1. The optical cable that connects together the slave corresponding to bits 12 to 15 of the MODE information and the preceding slave may be defective. Or, either of the slaves connected together with that optical cable may be
2. The voltage of the power supplied to the slave amplifier dropped, or a power fault occurred in the
3. Any of the axis control cards in the CNC may be

If the pattern of the STATUS information is B

1. The optical cable that connects together the slave corresponding to bits 12 to 15 of the MODE information and the preceding slave may be defective. Or, either of the slaves connected together with that optical cable may be
2. The voltage of the power supplied to the slave amplifier dropped, or a power fault occurred in the

If the pattern of the STATUS information is C

1. The slave corresponding to bits 12 to 15 of the MODE information may be
2. The voltage of the power supplied to the slave amplifier dropped, or a power fault occurred in the

•Power fault in a servo amplifier

If a power fault occurs in a servo amplifier, the FSSB alarm is issued. A power fault occurs, causing the FSSB alarm to be issued, if the amplifier control power supply voltage drops, if the +5 V conductor of the pulse coder cable is ground, or for other reasons.

If any of the axis control cards are found defective because of the above diagnosis, replace the axis control card on the motherboard (main CPU board).

•Replacing the axis control card

If any of the axis control cards are found defective because of the above diagnosis, replace the axis control card on the motherboard (main CPU board).

•Installation position of the axis control card
[For the LCD–mounted type]

Motherboard

NOTE

This drawing shows a motherboard without a PC (A20B–8100–014x). For motherboards with a PC (A20B–8100–014x, A20B–8100–046x, and A20B–8100–054x), the positions and the orientations of the connectors and the DIMM module socket differ slightly, but their relative positions are the same.

[For the stand–alone type]

•FSSB alarm on the sub–CPU board or loader control board

If alarm 972 is issued, indicating on the screen that an FSSB alarm occurred on the sub–CPU or loader, take appropriate action on the sub–CPU board or loader control board.

Screen display example