Security & Fire Protection Systems/CADDX


Dave - Mik here, again.  Last time I wrote you, I reported that the resistances on all three zones were the same with doors open and then with doors closed, which indicates to me that the loop wiring is OK.

This afternoon I swapped the wires from loop 1 and loop 3.  Remember zone 3 was the working zone and zone 1 (and zone 2) would not clear (yellow light was on constantly.)  With loop 3 connected to the zone 1 input, zone 1 still will not clear (yellow is on constantly.)  With loop 1 connected to the zone 3 input, zone 3 still works fine (yellow light goes out with door closed, and alarm bell sounds when door is opened.)

Hopefully the description of my little test makes sense.  

I believe that the same resistance on all the loops, plus the swap  test, indicates that the zone/loop wiring for zones 1 and 3 (I haven't yet tried swapping the wiring for zone 2) is probably OK.  

I believe it also indicates that the PCB is likely defective as the problem stays with zone 1 even when loops 1 and 3 are swapped at the PCB.

Hopefully I have adequately described my tests, results, and conclusions.  Let me know if I need to clarify them.

At this point, I'm considering replacing the CADDX circuit board with a new GE NX-4 board if it is compatible with my existing sensors and keypads, which preliminary indications are that it is.

What do you think?  Are there other tests that I can make to be more certain the problem is with the board?

Is the NX-4 board a direct replacement for the CADDX board, or is there something better that you can recommend?

Thanks again, Mik

Well, this is getting confusing. (There's information you sent in a separate post that I'll try to answer here as well.

First -- the end-of line resistor by definition should be located at the last piece of protection in the loop. So for your two-door loop, I'd expect to see it at the door farthest from the control box. However, installers sometimes take short cuts. Electrically, the EOL resistor can be anywhere in the loop, as long as it's in series. So you could connect one end of the resistor to terminal 1, splice one of the two zone wires to the other end, and complete a good circuit. The problem with that is that if you have a short on the loop beyond the resistor, the alarm will never go off when a door contact opens the circuit.

I think you would have mention it if you saw resistors hanging in the control

The second part is that you're reading a closed loop with no apparent resistor in it. And for zone 3, this seems to work just fine. And THAT does not make sense.

Add to this the fact that you took a working zone (3) and connected it to the zone 1 terminals and then zone 1 didn't clear -- that means, as you said, that the control has an issue.

The best test to confirm this is to remove the zone wires, and replace them with a 3.3K resistor directly across terminals 1 and 2. If the zone does not clear in that configuration, then the control is definitely bad.

You asked wither the NX-4 board is a direct replacement. I can't tell for sure. Looking at the specs, I think it'd be fine electrically for AC, battery, and protective circuits. What I can't tell is whether your keypad will be compatible. And I can't tell whether the standoffs in your 8600 control box will match the mounting holes on the NX-4 board. (I did see that the dimensions of the "can" or the box itself are different, so that's a concern.)

One thing I'd like you to try just to satisfy my curiosity... take a short piece of wire, and with zone 3 in its normal state, short out terminals 4 and 5. The zone should go into trouble.


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Dave Neuweiler


The design and application of burglary and fire systems for homes and businesses. Helping alarm owners understand how their system works. Helping to troubleshoot false alarm problems. Questions about monitoring issues.


Over a quarter century in the industry. Experience in installation, service, and monitoring centers. Training manager for a national protective services company; director of education and training for a national trade organization for for alarm dealers.


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