Simplex 4008 IDNet Issues

Hello all,

This is my first post here, I apologize if I do anything wrong.

I have a Simplex 4008 that is having some issues with the IDNet channel that I can’t figure out. A few things to note are that all the addressable devices are compatible and wired correctly, the class b jumpers are installed on the IDNet terminals, and I am using proper 18/2 fplr wiring. The system will operate normally for about a week at a time, but then I will randomly get this trouble:

“Card 3, IDNet Card, Class A”

Warm starting the CPU will clear this trouble. However, a few hours after clearing that trouble, the whole IDNet channel will shut down, and the panel will display the following troubles:

“Card 3, IDNet Card, XTRA”

“Card 3, IDNet Card, Short Status”

“No Answer” troubles on each addressable device

I checked the resistance across the IDNet wiring, and it read open as it should, so there does not seem to be a physical short across the wiring. Powering down the system for a while seems to resolve the problem for a week or so and then this cycle repeats.

Does anyone have any thoughts? Any help would be appreciated.


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The only similar situation I saw similar to this was on an original style 4010. Turned out replacing a smoke sensor that had gotten wet from a leak AND the cable going to it fixed the issue. Remember that an ohmmeter only places 0.4 volts across the circuit and the panel puts 28 volts across the IDNet circuit. The higher voltage from the panel can reveal leakage that the very low voltage from the ohmmeter cannot.

Is this an installed system or a test/demo/hobby system?

This is a home system, so it’s not actively protecting a commercial building. There is wiring for the IDNet outside however. Would replacing that wiring possibly solve the problem?

That outside wiring brings up another question. Did this issue start sometime after thunderstorm activity nearby? Is there suppression installed on the wiring going outside? Is the shield on the outside wiring connected to a good earth ground where the wiring leaves the end closest to the panel? What devices is the outside wiring going to?

This issue started a few weeks ago, but not after a thunderstorm. The only devices on the IDNet channel after the outdoor run are two 4908-9714 detectors on 4098-9792 bases. Both of them operate normally. I don’t have a good suppression on that lead though.

You should start splitting off wiring runs to see if there is one that resolves the problem. Then troubleshoot that run. I would start with the run going outside. If the system runs normally then that is where the problem is. If it comes down to any connected run still brings up the failure then the problem could be the system board. A known good device connected at the panel with no other devices or wiring could help make that decision.

Thank you, I will try that when the troubles start again. Do you have an explanation for the Class A trouble though?

The IDNet communication to the devices normally operates from the B+ and B- terminals. The A+ and A- connection monitors the voltage on the return side of the loop. The voltage on the A terminals is compared with the circuit source voltage. If the voltage across the A+ and A- terminals falls to a certain point the circuit turns on a relay. That relay connects B+ to A+ and B- to A- so the communications continues to both sides of an open loop. This also causes the Class A trouble to be generated. The relay is turned off at system reset or restart to test if the circuit is repaired.

My best guess is that something is loading the IDNet circuit causing the voltage across the SLC loop to fall to the level that causes the Class A circuit to trip. That loading is also causing the data to be garbled which can cause the XTRA trouble. That indicates a device is connected to the IDNet which is not in the program.