Simplex 2001 Nac card

I am repairing a 2001 and I have not been able to figure out the Nac card

It is a 2001-8023 board and the card is 556-874 what slot does it go in and what terminals are used

Without seeing the panel this will not be easy to help you with.



The 2001-8023 is the dual bay panel that has a single large motherboard.



Please tell me the following:


  • Simplex often placed labels on the dress plate indicating which card goes into which slot. Take a look and see if there is a label indicating where the NAC card goes.


  • Is there a march time card in the panel?


  • Finally can you provide some pictures of the panel?

Top bay

Control module is slot 1 slot2-8 are zone cards



Bottom bay



1-3 are zone cards 4 is city and 5 is nac card



No march card but I would like to get one so please explain how to install it



I cannot get a picture now as in I am not home

Are there any wires soldered between the numbered pads on the motherboard? If not, the panel is in default general alarm with steady ring NACs. If there are wires on the motherboard, those will have to be figured out.



There are four 24 terminal strips. Left and right sides at the top and bottom left and right. Each card position gets 6 of the terminals on each strip. The top left four cards get 6 terminals each on the top left 24 terminal strip. Same for the top right four module positions. The bottom just follows along the same pattern. For example the first zone card in slot 2 uses terminals 7 -12. 7-8 is the first zone on the, card 9-10 is the second zone on the card, 11 is annunciator output for first zone, and 12 is annunciator output for second zone. Can’t remember the polarity, but that is what voltmeters are for.



Adding a march time module takes adding some wires to the motherboard and cutting a diode on the control module. This will get you started.

Adding a march time module also requires cutting some jumpers on the NAC module.

Here’s a picture

I just want it to perform basic functions

Should I remove the jumper wires?

Looks like a spaghetti factory. Pure speculation is that the panel was set up for custom AHU shutdown, elevator control, or updated monitoring. Since there are wires next to bottom row PC slots 6,7, and 8 some modules were in those slots at some time. I can’t make out the solder pad numbers in the picture. If you could list some of the pad numbers with wires attached I can figure out what the use is on the cards. Start at the control module slot and a few zone module slots I should be able to help.

I can find those for you but is there a way to just make the panel run basic functions by removing the wires? If not I will get the info for you

Just from what I can see, the added wires all seem to be going to added terminal strips external to the motherboard instead of module to module. That may not inhibit default operation of the panel. The NAC module slot has no custom wires next to it, so the signal operation should be default. If this panel had a remote reset that was a normally closed switch wired between TB-1 terminals 2-3. TB1 terminal 1 is a ground connection for earth fault monitoring.

So what is your recommendation on what should be done

Taking another look at the picture, I see remnants of double stick tape on the right side. They are just the right size to mount additional relays like ice cube relays in sockets (2001-3005).



At your own risk, I think the panel will work as long as none of the wiring going off motherboard is shorted or otherwise compromised. Additionally I think the extra wires can be removed as they SEEM not to be involved in normal panel operation. On these systems standard general alarm, constant ring NAC operation did not need any added wiring to the motherboard.



The one module in this system that did require added wires is the city module. If you want to keep the city module operational, the wires between the city module slot and the control module slot should remain.

Ok I removed the wires and everything works the same

But I cannot figure out how tot wire the nac card

Terminals 1234 of the six it has says on the multimeter that it’s giving out 24vdc. But when I apply to the horns no sound

What is the 6 digit part number of the NAC card on the component side of the board?

OK, no answer, so I speculate again. Unless some special operation was needed, these systems typically were supplied with 2001-2076 (556-874) dual circuit NAC modules. When installed in PC position J13 they would use terminals 1 2 3 4 of TB4.

Polarity is>

P N S 13 on the card edge connector.

1 2 3 4 on TB4.

        • in standby condition - cannot sound horns - supervisory current only.
        • in alarm condition - can sound horns - full power supply current available - fused at 2 amps on card.



          When a zone is put into alarm the polarity should reverse as indicated above. If it does not check for jumper wires 15 to 16 and 29 to 30 on the NAC card being cut. Also check the control module for D25 being cut. These are the modifications for some special signaling, such as march time module being installed.



          I’m going to the den because the big TV is in there.

The card number is 556-638

And I tried the polaritys and it won’t work

The 556-638 number does not show up in the parts list I have. That is the number on the side of the card the parts are on - right? There is a 556-639 dual speaker circuit card shown but it is not compatible with the 2001 expanded repack panel.



If the 556-638 number is on the soldered side of the board, that is the number for a blank board with no parts on it. The number on the component side of the board is the number for the finished assembly. In a 2001 the same blank board can be used in several finished cards with different part numbers. Which one it is depends on which components and jumpers are installed. The number on the component side may be silk screened like the component numbers. The 556 may be silk screened next to a blank place that is used to write the last three digits with a sharpie like pen. Sometimes the entire part number is written with a pen. The finished assembly number is on the side of the board with the component parts.



Plug the control module in the upper left connector (J1). Plug in a zone card and the NAC card.

Your voltmeter should show the supervisory polarity on the NAC terminals.

The NAC circuit polarity should reverse when you activate a zone into alarm. Does it?

I found this good example of the part numbers in pictures of a NAC module on Ebay.

I don’t know the horns do not ssound either way I wire the nac. and I believe the model card I have is the 556-874 nac card


This may seem too basic, but I have caught people on this. Are there good fuses in the NAC card?



So I go back to the test in the quote above. This test will determine if the panel is working.



Do you know for sure the horn you are using is good?



The 2001-8023 panel puts out FWR power on the NACs. Be sure the device you are testing with is compatible with FWR. However, even if not they usually make some sort of noise.



When you attach the horn do you also have a voltmeter connected to the NAC? If so, what is the voltage reading?

I don’t understand this

It reads the voltage as 25.8 in alarm and Normal

The trouble led goes off when a 10k resistor is attached but the voltage drops to 16.1

I cannot tell if polarity changes do I need a certain multimeter?

I also got a march time card and I want to know how to get that to work and also cont. coding

And the card in the photo is the one I am using