Troubleshooting NFS2-640e SLC's

New to the forum, thanks for the add!

Working on an old NFS2-640e that’s showing a few invalid replies, but replacing the notifier modules makes no difference (FMM-1s and an FMM-101). However, only reading 15 to 16 VDC on these circuits, and that’s all the panel is providing, even when the circuits are removed. Resistance across the circuit wires (disconnected) is below the required 40-50 ohms and no sign of ground leakage (so far).

Am I wrong that there should be 24Vdc across these circuits? And could the low voltage be causing invalid reply faults?

Thanks for any help or pointers.

The SLC loop on that panel should read just under 15 volts dc at the panel. Check the modules for duplicate addresses. That will cause an INVREP for all of the devices with the same address. A bad module also could cause an INVALID REPLY on another address as well as its own. Look for any modules that could have water damage.

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Hi old and new generation onyx panels have “dead” address bug so you may need to change addresses for that modules, the voltage reading is fine, also clip mode only have access to address 01 to 99

Regards

Thanks for the tips pilot. Doesn’t appear to be water damage on or near these modules, but if a damaged module can cause a trouble signal on a different address, that could be happening, as there are some leaks in the building. Had another new INVREP show up inexplicably, this time on a detector, so will have to do some further digging, checking addresses and devices. Thanks for the help.

Thanks for the help fvilla, good tip! The address range on these is under 50, but we’ll try switching them to see if we hit some dead spots. Is there a list anywhere of what addresses to avoid?

hi, there are always random dead addresses no particular numbers, Another thing to check is that the panel has the latest firmware on it, the latest FW version is 27.

the INVREP modules are on loop1 or Loop 2?

regards

Good to know, thanks fvilla. I’ll check the firmware too next time I’m onsite. The INVREPs show up on one each loop, and it’s been the same addresses for a couple years as far as I can tell in the logs, but then a new one showed up on loop 1 recently.

If there’s a duplicate address, and we remove one of the INVREP’ing modules from that SLC, then in theory the panel (after reset) would show no trouble at that address anymore, yes?

Can do autoprogram to find if you have duplicate addresses

With SLC you won’t see a full 24VDC because you’ve got both power and communication (in the form of pulses) on that line. It’s even possible to read AC voltage on the SLC terminals. When you say the resistance across the circuit wires is below 40-50 ohms, do you mean that the SLC +/- wires at the panel have less than 50 ohms across them? If so, I’d say you’ve probably got a partial short, or waterlogged/faulty module somewhere on the SLC that’s causing your problem.
The 40/50 ohms max resistance spec is tested by shorting the SLC +/- at the last device then reading resistance at the SLC +/- at the panel, this test is only to ensure the length of wire connecting all devices is good (no weak/loose connections, corrosion, wire runs too long, etc)

fvilla, that’s a better idea than mine, thanks!!

theboginator, yes, I was referring to the specific SLC wiring guide’s method of testing resistance like you mentioned, so the wiring seems good.

And thanks for the helpful explanation about DC voltage readings. I thought the signalling was AC pulses superimposed on 24 V DC, so didn’t realize it would distort the readings that much, and since the modules are rated at 15 - 32 VDC, I thought this panel might have been too low based on what someone said on another forum.

So thanks for the clarification!

No problem - did you end up finding the module that caused the issue?

Yes - addressable devices will have a rating like “15-32VDC” because that’s the nominal voltage range; it’s similar to a 25/70V audio NAC where the actual voltage at any given point is dependent on the signal, with the given spec just being a min/max. If you search the forums for you’ll find a few fascinating topics where some guys have actually hooked an oscilloscope to an SLC to observe exactly how it works, each manufacturer is a little different. Really cool stuff.

Hoping to get back to that project soon, have been on other ones since I last posted, so sorry for the delayed reply. Thanks so much for the tips. I had a bit of a search as you suggested on the forums—interesting stuff. Always something new to learn!

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Finally got back to that project. Tried isolating the bad module, adding in a good module with the same address, and basically figured out it was the address that was the problem, not the wiring or the module.

So then did what I should have done earlier: Disconnected the batteries, re-booted, and voila, no more problems!