Simplex 4004 NAC Issue.

So tonight I wired up my 4903-9104 plate to my 2901-9846. That was on NAC 1. Because the way the strobe plate came to me, I had to put the EOL in the NAC 1 terminals on my panel. And that’s where the trouble begins.

All of a sudden, NAC 2 (which cannot be coded; it’s always steady per manual) starts doing march time with NAC 1. Both the panel and the strobes are going crazy with the Commander 3 flashing at 120bpm. Around the same time, the horn begins to hiccup and the panels indicators are completely spazzing out. The 9846 doesn’t even sound how it normally does! It sounds like a 9838 which must mean it’s underpowered! I assumed the wires made contact somewhere which caused the glitch, but when I removed the alarm, both were perfectly separate. I have no idea why it’s doing this or what’s going on; it has NEVER done this before even when tested before I installed it onto the wall, it worked like it was supposed to then. What’s the problem? I need help! I’m really scared my panel is broken and now I can’t use mechanical horns or coding at all! It has never done this in the past and NAC 2 has no reason to be coded. There is no way they are on the same NAC either because they are completely separate and no troubles are showing. I may try taking the Commander strobe down and see if that’s the issue. But I have no idea how NAC 2 would mysteriously code itself and follow NAC 1 and cause the panel to behave so bizarre.

Note: I have never changed NAC 2’s wiring to where it would mistakenly be on NAC 1 either.

Pic of strobe plate wire setup: https://www.instagram.com/p/BbsioHXlIOg/

Here’s the video.

I’m thinking it might be the strobe or it could have something to do with the audible silence being switched off on NAC 2 perhaps? But that still doesn’t make a lot of sense…

Check the NAC operation jumpers on the board. Either or both NACs can be coded.

I scanned the manual for NAC 2 and did not find anywhere where it states that NAC 2 can’t be coded. The manual does state that the factory default for NAC 2 is On Until Reset, which can’t be coded. But that jumper could be changed to the On Until Silence position, which can be coded.

First thing I’d do is remove the devices you’re currently using and swap in some known good devices on each NAC, then make sure the EOLs are connected properly, the panel isn’t indicating a NAC fault, and test the system again. If it continues to behave strangely, I’ve listed some additional troubleshooting steps below.

The troubleshooting steps I would do are in this order. If any of these steps fail, stop there and report back. Make sure you disconnect power from the panel before making any kind of electrical connection on it. I’d just leave the batteries disconnected for this since you’ll be constantly plugging in and unplugging the power.

  1. Disconnect field wiring and resistors from the FACP then power it up. The panel should indicate NAC trouble.
  2. Put the proper type of EOL Resistor across the terminals of both NACs then power the FACP up again. The panel should not indicate any NAC troubles. If it does, remove power, verify the resistors are the correct value and have not been damaged, and check again.
  3. Take a known good device from your collection, and connect it to one of the NACs with a temporary length of wire. Strobes and 2-wire horn/strobes should be on a NAC programmed for continuous. Put the EOL resistor after this device. Set the coding to continuous, then power the panel up. If it still indicates normal, initiate an alarm and see if the signal sounds as expected. If it works just fine, try setting coding options and make sure the devices perform properly. Note that strobes typically do not like coded power supplies and should be receiving continuous power.

If steps 1-3 are successful then we can likely rule out panel failure as the cause of your problem and begin focusing on device failure and/or wiring issues.

  1. Connect your NACs back up the way you originally had them, 1 NAC at a time. Use known good devices for this test, wire up the entirety of NAC 1 with the EOL resistor at the end. If the panel still indicates normal, initiate an alarm and check that the device works as intended. Once you have verified NAC 1 is working, reconnect devices to NAC 2 with the EOLR at the end of the loop, and test the panel again. If at any time during this process you notice a trouble condition occur, it’s likely you have a wiring issue (i.e. the wire sheath was stripped and the conductor underneath is touching bare metal or the connector of another NAC.
    Again, remove power from the panel prior to connecting wires to it. NACs are designed to withstand direct shorts during supervision (but not alarm), but if you were to accidentally touch 2 separate wires together and backfeed voltage into a NAC you could destroy it. I ruined my first MS-4 this way and a Simplex 4004 is almost certainly more expensive to replace so definitely be careful! Post a reply if you have any luck!

Yep, that’s the issue then! I’ll set it back to on until reset. Thanks for the help!

It was the NAC jumpers. NAC 2 has to be on until reset to override the coding from NAC 1.

So was this a programming issue? I always enjoy reading these posts about Simplex panels. I’ll never really understand them, but I still like to read it. As a wise foreman once told me, “I don’t mess with Simplex.” These devices seem pretty quirky and I appreciate quirky things. If anyone could describe the issue in layman’s terms, I’d love to read up on it.

Glad you figured out the issue. Having never owned a Simplex panel I can’t give stories of firsthand experience but I’d love to maybe get my hands on a 4006 or a 4010 some day. I’ve heard that the Simplex panels can be really sensitive and the addressable stuff (which is highly proprietary) is really hard to program and requires an expensive dongle to connect to the programming computer.
As for setting coding for conventional panels, the “software” they run (like the MS-2 and MS-4 for example) is really really basic. The panel reads a series of DIP switches upon startup to determine its configuration and, for the MS-2 and MS-4 it offers sync or non-sync continuous OR code-3 on BOTH NACs since the CPU likely isn’t capable of controlling NAC coding independently and small panels like the MS-4 or Simplex 4004 don’t have extensive NAC features.