Repair.IT – Repeller Car Alarm Remote Control

Most recent cars have some sort of remote control, usually to allow central locking and or activate the inbuilt security, engine inhibitor, etc. Cars from more than 10 years ago, might have central locking, but a lot of them didn’t. We have always added an after-market security system, which in the Honda Civic was a Repeller Car Alarm, fitted by the car dealer. These car alarms and keyless entry system usually rely on a key fob remote control that disables the alarm and unlocks the doors. Generally there is a battery inside that needs replacing from time to time. Don’t you just hate it when you try swapping the battery and the key fob still doesn’t work? Usually that is the time to use the spare remote, but what do we do with the one that isn’t working? That is what I had to do, a few weeks ago, to use the spare remote – I didn’t have spare batteries, but at least the spare remote works.

Most of the time, the electronics in the remote control or key fob are very reliable. They have to be, as they are carried in pockets with all sorts of items such as keys and coins. Many times they are dropped on the pavement – how often have you fumbled with the car keys and dropped them in the night time?

So what could go wrong – usually it is the switch that is failing. The simplest way of checking this is to open the key fob or remote control. Generally it is held together by one or two screws, then the housing comes apart. A 12V battery is usually found inside, depending on the car – I know some manufacturers use coin batteries, which don’t last long but is easy to replace. If the battery contacts look a bit green, then the battery has been leaking and the contacts will need cleaning, otherwise they will be covered in an oxide that has a high resistance which can prevent the remote from working. On the small circuit board, there is likely to be at least one switch, quite often two or even three. I didn’t have spare switches as these are surface mount and quite small, 6mm x 3.5mm in size, and 2.5mm tall – I did find them on eBay so ordered some and waited for them to arrive.

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The above photo shows the circuit board with the two switches, the red button is what is pressed when you press the rubber knob on the key fob. The white one is one of the replacement switches that arrived this morning. If you press the centre of each switch slowly, you should hear or feel a small click when the switch is activated. On my remote there are two switches, bottom one is to lock or unlock, and the top one is a panic switch – pressing the panic switch sets the alarm off, which is handy if someone is bothering you or trying to steal your car. I don’t think many remotes have this duress switch, but it can be handy at times. The lock/unlock switch doesn’t click which means it has more than likely failed.

If you have a multimeter, you can set it to measure resistance, then touch the probes onto each switch contact and press the switch – it is easy to say, but hard to do in practice. My switch is 6mm long, so after putting the probes on the switch, I need to use a small screwdriver to press the switch button. In my case, the resistance drops briefly but does not stay low, which confirms that the switch has failed. I can get it to stay low by pressing quite hard, but if I relax a little, it goes back high resistance. Ok, so to replace the switch.

I could use my hot air rework station to remove this switch, but I happen to already have a smd rework iron, which has tweezer tips. It is a simple matter of waiting a minute for the iron to heat up, then using the iron, clamp on both switch contacts, wait a few seconds, then lift the switch off the circuit board. Heating the contacts is fine, but when clamping on the switch, it does melt the switch plastic a little. To solder the replacement switch back on, we can do the same – but it is easier to use a conventional soldering iron since I need to hold the switch in place, solder one contact first, then solder the other end.
The replacement switch cost a princely sum of $2 for a packet of 20 – good price. I could have bought one if I could find a local supplier, but it would have cost a few dollars, so now I have 19 spares. Anyone need a switch?

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The photo shows it soldered in – yes, I know it is at a slight angle, but it should be fine. I tested it and it is working better than the original switch. However, during testing, the battery started to die. It did unlock and disable the alarm, but I could not get it to lock, unless I waited a few minutes for the battery to recover some charge. But at least the switch replacement is working, so now, I can order a couple of spare batteries – or maybe 5 because 5 costs less than buying 2 – how does that work?

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