433 MHZ device - why short life?

I have had (got) a few 433 MHZ devices -cordless front door bells and remote control lights and a remote weather station. The life of these devices seem to be short, the longest life, seems to be one of my remote door bell set ups at 7 years. Do the transmitters drift or is it the shoddy components that these ultra-cheap consumer items use. One problem is, no one offers any high quality devices. Has any one fixed these things? What sort of faults do they have. The problem is that I have not got a spectrum analyser and a proper receiver to actually find out which end is broken.
Frank

Look at where it is made. The workers there who make its parts and assemble it are paid almost nothing and might be uneducated children.
You are lucky that it lasted longer than one month.

Instead of subtle faults like frequency drift, I would expect simple ones like broken solder joints or corroded PCB traces, possibly broken COB bonds. Mostly problems that can be detected with basic measurements like circuit DC or RF level.

After locating some faults you'll have a clearer view of failure mechanism.

In my view there might be two more possibilities apart from frequency drift issues -
1) the receiver response may be decreasing over a period of time....
2) the gain of transmitter amplifier might be also decreasing over a period of time....

With regards,

Milind

Hi, it must be because of the poor quality. But im using 433Mhz tranmitters and receivers most of my custom projects. They practically never die.

" They practically never die. " What does that mean, what is their mean lifetime? Have you got any running for > 10 years?
Frank

Update.
I having looked at a couple of mains powered modules and the problem in both (two different units) was that the DC power supply is badly designed. Both circuits, use a low value series resistor in series with a voltage dropping capacitor then a bridge rectifier which feed a large reservoir capacitor with a zener diode across it. On both the zener diode had gone short circuit. the problem is that the output relay consumes two watts or so, so when the relay is de-energised, this two watts has to go some where which over stressses the zener, which dies. Also any mains spike energy ends up going into the zener at more or less full amplitude, which does not help. If the circuit had an inverter and sent the same current as the relay takes into a resistor when the relay is off, then the zener would hardly be necessary, as the load would be constant.
On a fan timer module, the DC line was 15V when the output triac was off, when it was energised the voltage fell to 7.8Y, due to the added current (~5mA) feeding the triac. This causes the timing cap to have to partially discharge via the internal input protection diodes on the CMOS 4000 chip. Not good for the chip as there is no current limiting!
Frank