I have a very old (c1986) Scantronic alarm unit which is working normally except that it is starting to hum fairly loudly: normally it is very quiet. This sort of hum usually only occurs when the power has been down for some time (eg 24hrs) and the battery is recharging from low-level. Does this hum suggest that the transformer or battery is failing? If so, how can I replace them without setting the alarm off?

Any ideas would be appreciated .

Rob, May 2010

Rob, sorry i forgot to say, if you enter the correct engineers code the panel sounder will start a high pitched ringing sound. This is normal and will stop when you remove the lid and thereby open the tamper switch. If you try to remove the lid without entering the correct engineers code the panel will go into full alarm mode, sounding the bells etc., and also dialling out to your monitoring station if you have this facility. You will then need the correct engineers code to reset this. Best of luck.

Terry, May 2010

Rob, certainly the battery sounds as though it needs replacing. This may well cure the humming. I'm not sure what size battery is in this model but it will be a 12volt lead acid either 7Ah or 3Ah. You can get this for about £12-£18 from screwfix depending on model. To change the battery you will indeed need to remove the main panel lid. There is a tamper switch on this. To remove the lid you first need to enter the Engineers code, which is not the same as the customer code. The default engineers code is 0 (zero) then enter, then 7890 enter. However, there is a high chance that this was changed by the original installer. But you could try it. Once the engineers code has been entered successfully you can then remove the lid, change the battery, do NOT remove mains while you do this otherwise you will lose all settings and will have to completely reprogram. When you have replaced the battery, replace the lid, key in 99 then enter, and you have finished. Whilst you have the lid off, check that the mounting bolts for the transformer are tight, which is about 1/3 the way down from the top on the right. If the default engineers code does not work, all is not lost. The panel can be completely reset to factory defaults and then reprogrammed. But I would strongly suggest that you get a good alarm engineer to do this for you. Best of luck mate.

Terry., May 2010

Thank you. It is a Scantronic 9100 model for which I have an engineering/installation manual but it does not help with this sort of problem. The humming is coming from the box itself rather than the keypad. However, I am pretty sure that the problem is with the battery since the life after power down is now only 6hrs whereas usually it is in excess of 24 hours (I do this regularly to prolong battery life). Do you know which battery I need to replace it with please? Presumably, when I open the box to do so the anti-tamper device will activate the alarm. Will keying in the customer code stop this?

Rob, May 2010

What is the model number of your alarm panel? I may be able to provide you with the installation/maintenance manual. Is the humming coming from the main control box or the keypad? It could be the transformer if its the main panel, or if its the keypad it sounds like mains noise which could be a broken down capacitor somewhere.

Terry, May 2010

Thanks -- I should have said that the battery was replaced around 15 years ago (and the alarm regularly powered down every six months ever since) but perhaps that's the problem? But how do I overcome the tamper mchanism?

Rob, May 2010

Has the battery ever been replaced?
It's not the original I hope?

Should be replaced at a MAX. of 5yrs, just because it appears to be charging does not mean it is.

acorn, May 2010