Hello,
Here's the setup: 1993 940 with CR814 radio (everything stock)
Recently rear door speakers were having this intermittent problem. I could still hear the tweeters but the low frequencies were coming & going. (The front doors & dash were fine)

I looked for a faulty crossover but the system does not seem to have any.
I removed the radio, sprayed some contact cleaner.
I also removed the amplifier (3533004 from under the steering wheel) to check if anything was burnt (it's all fine there, no smell, no busted capacitor).

Now I've reconnected the whole thing, but I cannot hear much, even from the front.
Volume know has to be turned up to the Max to hear the radio (from all 6 speakers)

Can someone please shed some light? I don't know where to look anymore and my local parts recycler does not have spare amplifiers.

Thanks
Olivier