Field Engineer’s Notes (From the Trenches)
The “Gotcha” is Sourcing vs Sinking Wiring (PNP vs NPN) and V+ Terminal Landing.
Sourcing (This Module): The load connects between the Output terminal and 0V (return). The module sources+24V fromthe V+ terminal throughthe FET tothe Output terminal.
- Wrong Way: Landing 0V to the V+ terminal and the load between Output and +24V. That’s Sinking (NPN) wiring. The MDL753 won’t work that way (open circuit / reverse polarity protection may block it).
- Correct: Land +24V DC Supply Positive to the V+ (or V1-V4) terminal(s) on the IC697TBB007. Land the other side of the load (solenoid/relay coil) to 0V DC Supply Return. Land the Output terminal (e.g., A1) to the load’s +24V side.
V+ Terminals: There are 4 V+ terminals (one per group of 8), labeled V1, V2, V3, V4 on the TBB007. They are notinternally tied. You must land a +24V wire to eachV+ terminal, or jumper them externally if you want a single-point +24V feed. Forgetting to land V3 causes “Outputs 17-24 dead despite LED being On” (because the FET has no supply to switch to the output pin).
Inductive Loads: For DC solenoids (>0.2A inductive), use an external flyback diode across the load(Cathode to +24V side of load, Anode to 0V side). The internal protection handles momentary spikes, but continuous inductive kick on a 0.5A point will eventually degrade the FET. If a point fails “On” (welded) or “Off” (shorted), check for missing suppression on the coil.
Real-World Applications
- Automated Case Packer (24V DC Solenoids): A 90-70 rack with driving 32 x 24V DC pneumatic solenoid valves (0.3A each). Groups 1-2 run the main lane diverters, Groups 3-4 run the flap folders. When a jammed flap shorted Group 3, only those 8 outputs dropped; the diverters kept running, allowing the operator to clear the jam without resetting the whole line.
- Water Treatment Plant (Pump Starter Pilot Lights): 32 x 24V DC LED stacks and seal-in relays for pump run/stop status, driven by MDL753. The individual point LEDs made verifying the “Pump 2 Running” light circuit a 5-second visual check during FAT.
High-Frequency Troubleshooting FAQ
Q: Point LED is ON (Green), but the field device (solenoid/relay) does not energize.
A: Missing V+ (Supply) or Wiring Polarity.
- Check the V+ terminal for that group on the TBB007. Is +24V DC landed and tight? If the V+ is floating, the FET has no source voltage—current can’t flow, so the load sees 0V across it despite the LED indicating the logic command is active.
- Verify Wiring Polarity: Output terminal → Load +24V side; Load 0V side → Supply 0V. If you swapped and landed Load between Output and another+24V source (not through the module), the module can’t switch it.
- Check Load Integrity: Is the solenoid coil open? Measure resistance (should be 20-200Ω for a 24V DC solenoid). If OL, the load is bad, not the module.
Q: “FUSE” LED is ON (Amber/Red) for a group, those 8 outputs are dead, others OK.
A: Group Short or Overload.
- The electronic fuse tripped. Turn the output group Off in the PLC (write 0 to those %Q bits) or power cycle the rack to reset the electronic fuse.
- Find the Short: Disconnect the field wires from the 8 Output terminals of the faulted group. Power the group back On (command all 8 On via PLC force). If the Fuse LED stays Off, the short is in the field wiring. Reconnect one wire at a time to find the culprit.
- If the Fuse LED immediately re-illuminates with no field wires connected, the module’s group driver is damaged (unlikely but possible from a severe transient). Swap the module (Hot-Swap if rack allows).
A: Yes, with the correct Terminal Block.
- The is mechanically/electrically compatible with the RX7i backplane (VME64/PCI hybrid).
- It requires the IC697TBB007 Terminal Block (Series 90-70 style), notthe RX3i IC694TBB032 (different keying/pinout).
- Configure it in Proficy Machine Edition as “” in the appropriate slot.
- Ensure total backplane current draw (CPU + I/O) is within the PWR710/711/PSA100 capacity. For heavy loads, confirm the +5V backplane rail isn’t overloaded (check PWR module FLT LED).
Please note: The listed price is not the actual final price. It is for reference only and is subject to appropriate negotiation based on current market conditions, quantity, and availability.
