Guide to repair Bosch H12 alarm siren

[sparky2]

Hi All, VCDS pinged up low battery on the alarm siren (Bosch),and upon testing had a very low output noise, so I thought I would cut it open and have a look inside to see if it was the common problem of the batterys leaking. So cutting round the seam of the unit with a junior hacksaw it came apart, the batterys had leaked but on cleaning the PCB it hadn't damaged the copper tracks,this unit was different to my last one where the batterys leaked all over the components and rotted the tracks etc  so a bin job !  This Bosch one was designed well as there was only a transformer and the batterys on one side of the PCB and components on the opposite side so not much to damage. I tried to find the correct edge mounted batterys,no chance,but found some normal Varta 3V150H ones so ordered them from buyabattery.co  (£13.47 inc p+p for 2 ) then soldered some wires onto the ends so I could mount them on there side, and put a band of heatshrink round them to hold them together,cleaned the PCB and painted it for protection,fitted batterys and sprayed both sides of the PCB with silicon spray to keep damp at bay,cleaned the cut edges of the case with a cotton bud with meths and stuck it together with Dow Corning 3145 non corrosive sealant as I had some in stock, tested on car then refitted with metal case etc.

[sparky2]

Component side of PCB 

[pikpilot]

Thank you for photos etc. I am sure it will prove useful.

 

Here is a link to the same issue on the H09 version in case future searchers need it:-