Alarm horn battery problems?

Hi all, I've recently sorted out my faulty alarm horn and thought I'd just post it up in case it helps others......
I heard it was a common fault and that the battery would just need replacing but this doesn't seem to be entirely accurate. The common problem is that the backup batteries fitted tend to leak over time, this eventually seaps down the contacts,onto the pcb and destroys some tracks and components. If you catch it soon enough you might be lucky but alas I was not.
First the alarm horn will need opening, a hacksaw does the job....
Then you'll find this ...

And this is the damage I faced :

I had to fit two links as shown and replace three surface mount resistors that were damaged but having done this I refitted it and its working perfectly.
Saved me £ 88 for a new one and not that hard to sort out .......

[thebluewhale]

Nice work fella

Just for the fact you replaced surface mount transistors

[Oli18]

Only 8 posts and already contributing! Thanks for sharing this

Oli

[Singh]

Thanks Darren, this is a very good post.

[jayzee]

One for the sticky?

cheers for the positive comments guys. I'm an electronic engineer by trade so I have to deal with surface mount components and explosive/corrosive damage all the time......
The only tricky thing was working out the value of the components without a schematic of the circuit .
I found a good hi@def picture of a good alarm pcb here :


Click on the image for a larger version. With this I could tell that the surface mount components with numbers are resistors and if you google the number on the front you can find out the value.
The plain smc's are capacitors and luckily these weren't damaged on mine, as they have no value printed on them.
With talk of making this a sticky I thought I should add a few more details........
As a guide to anyone attempting this I would equip youself with a scalpel,soldering iron,some isoprop or other pcb cleaning solution, a multimeter and a nice printout of the highdef image.
1 - go very careful when cleaning off the fuzzy acid debris as its easy go knock off a smc like I did , doh !
2 - using the scalpel scrape off the coating on the tracks in the damaged area.
3 - using a multimeter measure from point to point along each track for continuity to check for breaks - I had two that I linked.
4 - check the solder joints on the components as the acid tends to make them dry away from the pcb pad. I found it worked well to scrape the solder's surface with the scalpel to take off the dried acid before resoldering.
5 - be very careful not to knock any smc's off throughout the whole process and you'll make your life easier....
Just to note that the chip to the right of the large one, above the likely damaged area is the eeprom chip which is basically the brains of the system and due to its well thought out placement next to the battery contacts means any damage from leakage will prevent the circuit working !!!
A good thread to check out is this :

http://www.tt-forum.co.uk/forum/view...it=alarm+siren
This contains a nice guide to replacing the batteries too.......
All in all it sounds a more difficult process than it is , if anyone is attempting this and has issues just drop me a pm and I'll be glad to help........

[Conan_the_Librarian]

Added to repair sticky. Thank you Daz.g

[MikeSF]

Originally Posted by daz.g

cheers for the positive comments guys. I'm an electronic engineer by trade so I have to deal with surface mount components and explosive/corrosive damage all the time......
The only tricky thing was working out the value of the components without a schematic of the circuit .
I found a good hi@def picture of a good alarm pcb here :


Click on the image for a larger version. With this I could tell that the surface mount components with numbers are resistors and if you google the number on the front you can find out the value.
The plain smc's are capacitors and luckily these weren't damaged on mine, as they have no value printed on them.
With talk of making this a sticky I thought I should add a few more details........
As a guide to anyone attempting this I would equip youself with a scalpel,soldering iron,some isoprop or other pcb cleaning solution, a multimeter and a nice printout of the highdef image.
1 - go very careful when cleaning off the fuzzy acid debris as its easy go knock off a smc like I did , doh !
2 - using the scalpel scrape off the coating on the tracks in the damaged area.
3 - using a multimeter measure from point to point along each track for continuity to check for breaks - I had two that I linked.
4 - check the solder joints on the components as the acid tends to make them dry away from the pcb pad. I found it worked well to scrape the solder's surface with the scalpel to take off the dried acid before resoldering.
5 - be very careful not to knock any smc's off throughout the whole process and you'll make your life easier....
Just to note that the chip to the right of the large one, above the likely damaged area is the eeprom chip which is basically the brains of the system and due to its well thought out placement next to the battery contacts means any damage from leakage will prevent the circuit working !!!
A good thread to check out is this :

http://www.tt-forum.co.uk/forum/view...it=alarm+siren
This contains a nice guide to replacing the batteries too.......
All in all it sounds a more difficult process than it is , if anyone is attempting this and has issues just drop me a pm and I'll be glad to help........

Hi,
The post would really help me as I too have issues with my Alarm Horn and want to avoid forking out for a new one. I managed to salvage my horn by removing the batteries and running without them. Recently I decided to install an external battery pack but since fitting it the electronics no longer function. I didn't get the polarity wrong so this issue might be something to do with the fact that the inside of my car flooded when the air intake drains become blocked and +2 gallons of water ended up inside the car (What a **** design!). Anyway, watch out for this.

For some reason I cannot download your pictures. Is there any way you can add them again?

Thanks

Mike

PS, if you want to check the drains on your car you will need to put the car on ramps and check them from under the car just behind the engine. You are looking for two 1" pipes with a crimped end in the shape of a cross. Open the flaps and dig out the muck then flush out with a hose placed under the air intake box. Check both sides of the car.