Remote central locking stopped working

[hamx5ter]

Ok, i've got an NB8A with the factory remote & alarm. This is the one with the three blue buttons in different sizes.

It doesn't lock / unlock the doors anymore.

I noticed over the last couple of months that the range over which the remote worked had dropped substantially, but now, no un/locking at all.

I've got a spare remote and tried that one - same result, so it can't be low batteries on the remote.

Both locks work when the key is used or if the driver's door is locked manually from the inside, so it seems the actuators are fine.

Arming / disarming the remote turns the alarm on / off, so no battery issue (although it does look weak).

Any ideas?

I'm no electrical guy so i'm just trying to see if there is some simple troubleshooting to be done before i take it to the shops and pay up.