Renault 5, Renault 19, Renault 25, Renault Espace (late mk1) Renault Clio (early MK1).
The transmitter (Plip) has a TEA 5500 Phillips chip as does the receiver. These are programmed before fitting to the circuit board and need to be a matching pair.
When you withdraw the receiver, it should have an orange sticker with a code on it. Likewise, the transmitter (Plip) will have an orange sticker with a code on the circuit board. These numbers need to match.
You can test the transmitter (Plip) with your camera phone, pressing the button. There is no easy test for the receiver except for plugging it into the car!
These chips fail if they get wet or even with moisture in the air. Cars with sunroofs may have leaked on your receiver over the years, the aerial seal may have leaked or even just the moist air may have damaged it!
Best bet is to get hold of a known working matching pair. Mike at GT Turbo Spares has several sets, alternatively they do pop up on e-bay every so often.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... _685wt_811