Radio Suppression Relay mystery
 

Last October whilst trying to rectify another fault (turned out to be fuel pump), I replaced the car's old radio suppression relay with a brand new one (sealed in a bag from Volvo main stealers). Immediately prior to fitting the new one I didn't have the following problem but immediately afterwards I did. Whilst turning the volume knob on the radio/cd player there is all sorts of awful noise and interference but once the volume is adjusted to the correct level there is no awful noise (at this moment in time I am reluctant to remove the new one and put the old one back in as having removed the old one last time I just couldn't get the new one back in no matter how hard I tried and in the end a neighbour did it for me)

Could the new one be causing this problem?

Totally unconnected as far as i can see Ellie, it sounds like a very noisy volume control pot to me. Quick method of basic cleaning is (with the radio off) turn the volume up and down quickly several times, all the way in each direction. Granted you need to be a bit of a contortionist to manage this but it's possible - just!

If you are able to remove the radio and locate the volum control pot, squirt some contact cleaner into it and repeat the up/down quickly several times. Should cure it. :thumbs_up:

Once upon a time you could disassemble the variable resistor 'pot' and using a nice soft 2B pencil (lots of carbon their) to re-constitute the trackway. Bob :)

Thanks guys, must just be an awfully big coincidence! Its actually the volume of the Sony CD player (I only play CDs, not radio) which is programmed/linked to the Volvo radio/cassette player. I have to choose a particular station to get the CD player to play through it, the car came fitted/operating thus so. (I hate MP3, too thin a sound, no point trying to convert me, I love my 10 changer CD player!).

I have just learned the word 'potentiometer' from Google. Thanks, nice word that. Does it meter the potential of something?

I'd be the last person on here to try and persuade you MP3 was a better media than CD Ellie! As an apprentice, i worked on the 1st/2nd gen CD players before the system (as we know it now) was officially launched 33 years ago yesterday. As such i've got a soft spot for it.

Anyway - potentiometer - you've pretty much guessed it but not quite. Imagine a 12V battery, like in your car. Now imagine you have a 6v bulb you want to light. The 12v battery will blow it pretty quick. With a potentiometer you can "tap off" 6v for the bulb.

Now think of a bucket of water, lift it 12ft in the air and it has a 12 ft head of pressure courtesy of gravity for the water to flow out of it and water your plants. Trouble is, that will flood your plant pot, washing soil away from the roots and the plants can't absorb the water quickly enough so they die.
However, if the bucket is 6 ft in the air, it only has a 6 ft head of pressure to water the plants with which they can cope with, it will take 24 hours to drain so you can come back next day and refill it.

Now imagine a device that you can simply tap off the water level you need.

In more technical terms, the potentiometer is a potential divider where the potential is the voltage. It has 3 legs, one to connect to earth/0v, the other to connect to battery +ve/12v and the third to tap off the voltage you need - this is called the wiper.
It's usually a carbon track resistor and the wiper slides along it to enable the required voltage to be "metered" off the potential. This is why Bob was mentioning using a soft pencil to revive the carbon track to restore operation on a worn component.

I hope that all makes sense, i've tried to keep it simple while not insulting your intelligence, i hope i've succeded! For a more in-depth explanation, have a look at the Wiki page, it goes into more details abot the plethora of uses of potentiometers - you'll be amazed just how many you've got in one form or another!

https://en.wikipedia.org/wiki/Potentiometer

Thanks Dave, thats interesting! I will have an attempt at finding mine whilst armed with the right pencil one day!

I don't think a pencil will help these days Ellie! This stuff would be a better bet :

https://www.ebay.co.uk/itm/9893-MANN...n/303081768191

Squirt it into the offending potentiometer and "exercise" it like i described above. :thumbs_up:

Sorry, not paying proper attention! I do have aerosol switch cleaner. One day I'll hunt out my potentiometer and have a go with it!

That conjures up some strange mental imagery involving a cave-girl type character, a spear and a giant, living predatory potentiometer! :eek::tounge_smile:

Think it was the "hunt out" phrase that triggered it! :lol:

No, that's 'hunt down'! Hunt out means to look for, I will have to look hard as I am not very well up on electronics but I an at least Google image!