Spooky P.a. Activation

[SIMONADT]

Hey everybody, hope you're all having a good weekend..... (while someof us are on call )

Anyway, a couple of weeks ago i was called to a large orange branded diy store for a false activation of a PA switch (silver box with two red switch's style) My login name suggests the company i work for so you might be familiar with the type. There are two of these on the same circuit running off a n old Galaxy 500 series - (512 i think)

They are not the newer styled switches with the built in resisters and dip switches, they are the ones with the reed switch and the ols school silver plated terminal. My question is this... the zone has gone into high resistance within the log in the past and calls the police about twice per week. I have replaced the switches, re-made the wiring and of course, told the Manager of the store to ensure there is a green window in the button housing everyday and to check the state after activation. It has been confirmed by the Police as well that NO MANUAL activations of the button have been witnessed/recorded.

Any ideas? (I have already checked the A/C number with the ARC to ensure the account has not been deactivated etc

Many Thanks

Simon

[arfur mo]

hi simon,

i'm not familiar with the panel, but my 1st reaction is after what you have already done is to check for any earths on the system. simply meter on voltage range from each side of the 12 volt rail to a good earth to see if there is any leakage, if so eradicate it.

(if anyone don't know why that test is done i'm happy to do a tips section on it - just ask).

can you split the button's up onto separated zones or move one pab to an existing (behaving) pa zone even for a temporary period? if the cables and joints are sound i'd suspect you might have a faulty expander, but have a real close look for any naught repairs hidden behind girders or the likes by some lazy git of an engineer (very common fault). a slim chance of RFi through a cable passing near some high power or motor equipment perhaps.

although you have change the old style pab's it's worth doing a test with a meter over say 10 operations and ensure the resistance measurement is the same each time, often a cracked reed will go h/r if you 'worry' it enough.

regs

alan

[SIMONADT]

Magic i think the chances of running in a new cable for seperating the switches is nearly impossible because of the location of the till to the position of the panel (and the cable run is 40' up in the air ) but i will check for earth. Also, being as there are only three engineers over here in the Isle of Man, there is a very slim chance there will be any cr@ppy fix's as we all know they will come back to haunt us!!!! B)

Right, Monday morning my meter will be working its behind off to find the location of the problem then!!!!!!!!!!!!!!!!!

[magpye]

Magic i think the chances of running in a new cable for seperating the switches is nearly impossible because of the location of the till to the position of the panel (and the cable run is 40' up in the air ) but i will check for earth. Also, being as there are only three engineers over here in the Isle of Man, there is a very slim chance there will be any cr@ppy fix's as we all know they will come back to haunt us!!!! B)

Right, Monday morning my meter will be working its behind off to find the location of the problem then!!!!!!!!!!!!!!!!!

Magnets, can any sort of magnet get close to the PAs, loud speaker for example at a checkout?

Have come across this sort of problem in the past, someone buys a new set for their car and at the checkout passes over the PA - F/A, something worth looking for.

[Guest Dave the alarm man]

normal, cable / device / enviroment or controls (one or more ) thing

twist join the pair @ control end, measure the cable should be low ohmn's (compare to or swap to spare pair if present)

or maybe duff expander ect..... link it our & leave on soak test?

[spider]

Checking the reed for damage as has already been said, also check that the magnet is fully 'home' in the plastic holder and that the friction screws are tight (this will make a difference if the unit is mounted with the buttons showing on the top (not good practice))

Cable to earth, (maybe staple if you use them) remove from panel, twist together and either perform an insulation resitance test (Not 1000v lol) or use MOhm range to check for leakage.

If you have spare circuits at the panel end, try moving the circuit at the panel (could be pcb tracking /moisure ingress??)

Replace resistors at the device, I have these go high in the past.

Could be a disgruntled staff member knocking hell out of it? (pensioners can get a bit cranky lol)

Good luck

[SIMONADT]

thanks all

will try tomorrow!!!!!!!!

[arfur mo]

i seem to have had an earlier post removed, anyone care to own up and tell me why?

a faster and easier way initally to test for earths is to place your meter on 20 volt range and measure between each rail and a good earth point, you might see about 1 - 2 volts which can often mean induced voltage from say fluorescents rather than a true earth, modern dvm's have very high input impedance compared to the old swing needle types i cut my teethe on (mIni test & TMK500 those were the days )

Regs

Alan

[amateurandy]

a faster and easier way initally to test for earths is to place your meter on 20 volt range

AC, DC or both?

[camerabloke]

yes