Siemens LMV5 Quick Start Manual page 128

CANBus Wiring "AZL not on Bus"
When the AZL5 displays "AZL not on Bus", or is stuck in "System Test", this is typically means that
there is a voltage problem on the CANBus. This usually does not mean that the AZL5 needs to be
replaced. Make sure that the neutral and chassis ground are bonded, meaning having no electrical
potential (voltage) between them. The 5 points mentioned on the previous page should also be
checked, especially points 1, 2 and 4.
It is possible that one or more actuators are being overloaded and are consuming too much power
from the CANBus. Voltage should be checked by probing the CANBus terminals.
There should be 12 volts AC between 12VAC1 and GND.
There should also be 12 volts AC between 12VAC2 and GND.
Voltage between 12VAC1 and 12VAC2 should measure 24VAC.
If the voltage is significantly less than these values, the CANBus is overloaded, a short exists, a
fuse is blown, or some part of the CANBus is improperly wired.
It is much easier to troubleshoot the CANBus in pieces rather than all devices at once.
When a CANBus problem is discovered, all actuators and the O2 module can be disconnected,
so that ONLY the AZL5 is connected to the LMV5.
The actuators / O2 Module can then be connected one by one, to see when the CANBus fault
appears. This method is easy to perform since the actuators / O2 Module have plugs that can be
connected and disconnected with ease.
Grounding
The second largest category of wiring problems concerns the grounding and the shielding of LMV5
components.
The LMV5 has three different types of ground, each with a different function. The three types are:
1) Protective earth or chassis ground (PE)
2) Functional Earth or Shield (FE)
3) Reference Ground (Labeled as 0, M, or GND, hereafter labeled as 0)
All PE's that exist on the forward facing plugs (white plugs) of the LMV5 are bonded together.
All 0's that exist (green plugs) are internally bonded.
FE's are bonded to one another on the individual internal circuit boards of the LMV5,
and are then bonded to the 0's with capacitors on each individual board.
At the 12VAC transformer's 4 pin SEK2 plug, Pins 2 and 3 are tied together, thus connecting 0 and
FE directly on the circuit board that has the CANBus connectors. It is highly recommended that
SEK2 Pin 3 on the transformer, and X52.4 are connected to chassis ground (PE), effectively
connecting 0 to chassis ground (PE). This also connects 0 and PE directly to FE, on the CANBus
board only. FE on other boards is isolated from 0 with capacitors.
In short, FE are exclusively for cable shields, 0 is the reference ground for all low voltage sensors,
and PE should be connected to the main grounding lug (main chassis ground).
Note:
The main step down (480VAC to 120 VAC) transformer must have the neutral and
chassis ground bonded together on the low voltage (120VAC) side.
All other devices connected to the LMV5 (such as a VSD and blower motors) must
also be grounded to chassis ground.
LMV5 QSG Rev 4 Sec 5 Pg 2 www.scccombustion.com