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www.technozen-electronics.co.uk

pecker wrote: wrote:

hi can anyone help
my mg tf , when press keythob to lock , car lights flash and it locks , when press keythob to unlock car lights flash but car does not unlock
any ideas what the cause is
thankyou

Remove the passenger side footwell light panel (2 crosshead screws) if you look behind you will see the side of the Pektron BCU/SCU, there is a steel strap holding the unit in place, undo the screw (it may be a tamper proof Torx) bend the strap down and pull the unit out towards the passenger footwell, remove the 4 wiring plugs to release the unit.

With the unit on the bench tease the plastic cover open with a couple of small screwdrivers to release the board, on the board you will see the 5 relays, the relays are double units so 10 relay functions in total (2 relays in 1 unit) Identify the central locking relay from my image below (the relay has been un-soldered in the image but you can see where it sits on the board) if you turn the board over you will see the soldered pin-outs of the relay, if you open the attachment at the bottom of this post you will see my drawing of the relay pin-out positions, with a multi meter set to ohms measure the resistance across the 2 coils (one relay coil for unlock and the other relay coil for lock) you should get a reading of around 200 ohms on both coils (measure across pins 1 & 2 then 1 & 3) if you find one coil open circuit then you have found the fault (this is a common failure on the Pektron board giving exactly the issue you have)

If this is the case then you have a couple of options, replace the relay yourself as there are plenty for sale on Flea Bay from £5 to £7 per unit, or send the board away as suggestions on the posts above.

Whichever option you go for its best to replace all the relays on the board that have Pektron written on them as these are the relays that the coil windings fail by going open circuit.


Relay identification (note: central locking relay has been removed ready for replacement)

Excellent.
Here's the pdf.

Could this be my problem too??

Car locks with fob and alarm sets, when I unlock with fob it blows the under bonnet fuse and sounds the alarm.

I can't stop alarm until I fit a new fuse and turn off immobiliser.

If I unlock with the key it's the same.

Currently I haven't replaced the blown fuse so have no central locking or immobiliser.

It's a square Lucas fob btw.

That sounds more like you have a wire(unlock) from the lock that is grounded to earth. Frayed or broken.
Check the cable loom that enters the door.
And also the famous boot hinge loom too.

cheers for the info,
pins 1 & 3 got 220 ohms but nothing on pins 1 & 2
so ive sent for some relays , should be here middle of week ,
ill replace the relay and let you know how it goes
thank for the help
Dave