Tamper fault on PIR

[phantomzone]

I've recently been doing some redecoration which necessitated the removal of a PIR. When I put it back I seemed to have damaged it somehow. The alarm panel is now showing a constant tamper fault light which I can't deactivate.

Usually just removing and replacing the cover does the trick but this time it's with no effect. I don't know how the tamper sensor works so can't work out what else to try with the PIR itself.

The system is, quite an old, Scantronic 4700 system with wireless PIRs.

I don't have the engineer code for this box only the general activate/ deactivate code.

Can I replace the PIR using something generic? I'd rather not have to replace the entire system as this one does the job very well normally.

Any alarm techies here who can advise?

Ham

[Andrew Gabriel]

In most (particularly cheap, home) PIRs, it's nothing more than a mechanical contact, e.g. a microswitch, piece of bent metal, or a spring pressing on a PCB mounted minature push button mechanisn.

In some more expensive PIRs, it's a signal generated by the microcontroller. It will operate if the unit loses power (probably not in the case of a wireless sensor) or if the microcontroller detects a fault in the unit.

Some panels will require (or can be programmed to require) the engineer code after a tamper fault even if the fault is cleared. Sounds like you know from past experience that isn't the case with yours though?

Wired ones, yes. Wireless tends to require the exact same part, which are usually no longer available by the time one breaks :-(. However, I don't know about your Scantronic.

[Mike Harrison]

One common mechanism is a spring fitted to a pcb-mounted pushbutton -maybe this fell off... The tamper switch will be a mechanical switch of some sort - have a good look and you should be able to find it, and then you may see why it isn't working when the lid is replaced.

[cj]

Hi Scantronics systems are still amongst the most reliable and Cooper Menvier who now are Scantronics have a very good archive. However the 4700 series is no longer with us being superseded by the 500r and now even that is out of date. The 4705 pir you refer to IIR has both rear and front tampers and was prone to a rear tamper fault if the cover was hit causing it to fall off. Remove the pcb and hold it in your hand pressing both the front and rear tamper micro-switches then try resetting the panel. When testing the 4705 PIR detector you must remember that the detector will go to sleep after an activation for about three minutes to conserve battery power.

If you have the engineers code you can put the panel in walk test instead. I have a PDF of the manual should you need it to help in your struggle. HTH CJ

[phantomzone]

Hi, firstly thanks to all of you for your input it is as always greatly appreciated.

I found the microswitch. Once I pushed it down I can hear a definite click which removes the fault from the panel and leaves the tamper light on. When I put the cover back on the fault light re-appears thus preventing me from clearing the tamper light.

I looked on the other working PIRs and I dont see what keeps the tamper switch depressed. i.e. when the cover is lifted it would raise and then show tamper. So I cant seem to work out how that switch is actually activating.

Andrew- In the past when i replaced the battery on the PIR it would show tamper and then I would just need to put in the user code and it would clear. So in that case it didnt need an engineer code.

CJ - I couldnt see a rear tamper (I removed the whole PCB from the casing to look at the back. On the front part of the PCB it has a 4700 sticker so I assume that maybe the 4700 and 4705 PIRs differ in this respect.

I've put some pics here

you have any further suggestions...

...although I'm getting the feeling that the new TV will have to wait a bit longer until a new alarm is fitted :(

[cj]

Hi The tamper switch is the small micro-switch on the corner of the PCB. It is activated by a plastic rib on the inside of the lens cover a common fault with all Scantronics pir's is that if the sensor is not exactly flat to the wall the switch will not make. A very easy fix is to carefully bend the switch arm . To do this hold the switch closed with one finger and gently bend the arm away from the switch making sure the bend is between the actuator pin and the free end. (IE The steel strip is fixed to the switch body at one end it then passes over a raised actuator pin about 1/4 of the way down the switch length before continuing for the length of the switch.). Also check that the cover fits snugly they should locate with a click . HTH CJ