Classic cars forum & vehicle restoration.

peppiB

Annoying fault on radio in my 1990 Merc. It is a Blaupunkt. The original radio/cassette which I didn't use was replaced with a radio/cd. It works fine for about 20 mins then goes off. Turn it off, wait 15 mins or so and then it will work for another 20 mins. I have tried 2 different radios and they do the same thing. I have replaced the speakers (the originals were well past it and gave a distorted sound) changed wiring, changed connectors, renewed the aerial (electric) and still can't get the thing to work
Any ideas? (does the same with both the radio and cd player)

ukdave2002 · Joined: 23 Nov 2007 Posts: 4104 Location: South Cheshire

I'd wire a volt meter to the supply, quick check when the rad goes off will determine if it's a supply or unit fault...intermittent faults are the worst !

Dave

Greeney in France · Posted: Thu Mar 27, 2014 7:26 am Post subject:

Has your merc still got the 'aluminium' fuses
These create so many niggles as they corrode against the bronze terminals.

Take them out clean all the terminals with a small soft wire brush and replace then all with Copper/brass replacements.

Sounds like a 'heat' related issue when something 'wire, terminal' heats up it separates enough to cut contact.
If all the wiring is exposed turn the radio on and apply heat from hair dryer to see if you can 'make it happen'..
_________________
www.OldFrenchCars.com

We do these things not to escape life but to prevent life escaping us

peppiB · Posted: Thu Mar 27, 2014 9:57 am Post subject:

Thanks guys.

Greeney - yes some of the fuses are still the aluminium ones and occasionally have their issues. I have a bag full of copper/brass ones so will do a complete clean and replacement

Dave - usually when the thing goes off I am out in the car with the mentally ill epileptic girl I am carer to and she goes spare at the thought of any breakdown so if I were to pull over and take the radio out and start using the volt meter she would probably go into a seizure!! The next time I take her to see her mother I will secrete the meter about my person so she doesn't suspect anything and then take the radio out whilst she is indoors talking (something she is very good at!!)

Greeney in France · Posted: Thu Mar 27, 2014 10:02 am Post subject:

Bitumen Boy · Posted: Thu Mar 27, 2014 10:51 am Post subject:

Good suggestions here, but something else comes to mind for me. What I've noticed with car radio/CD units (though admittedly fairly old ones) is that they seem to draw more current and generate more heat than radio/casette units used to. Now what I'm thinking is if the ventilation (and thus heat dissipation) around the unit is poor it might be getting hot enough to activate some sort of over-temperature safety cut-out. A fair number of electronic devices have such things nowadays, usually they reset automatically when the unit cools down sufficiently.

A few years ago I was using an old laptop which would get quite warm anyway, but it got into a habit of just shutting itself down while I was working for no apparent reason. It did this a few times before I cottoned on why. What was happening is that our cat would come up on the table while I was working on the laptop, and after a bit of fussing would settle down behind the laptop where the cooling fan blew warm air out of the vents - you know what cats are for a warm spot. Trouble was that she effectively blocked the vents, stopped the cooling and so the laptop would overheat and cut out... solution, shoo the cat away to sleep somewhere else Laughing

peppiB · Posted: Sat May 10, 2014 4:20 pm Post subject:

Quick update on this.

Had the radio out today whilst I changed connectors. I had it laid in the car playing whilst I worked. Came to return it to the space in the console ...... and burnt my hand when I picked it up. Just the left side of the radio was very hot.
I have another spare Blaupunk so wired that one in,left it on and after 10 minutes it, too was too hot to handle

Think you have it spot on Bitumen Boy

ajlelectronics · Joined: 04 Oct 2010 Posts: 168 Location: Gloucester

Much more likely that you have a wiring error. Put it on the bench wired to a pair of speakers and retest it. It could be that your car speakers have a common negative rail, which modern heads will not tolerate. I would lay bets that it is down to the speaker wiring in some way.
_________________
Evans Waterless Coolants
Find this and more at http://www.classicmicrocars.com
Sat TV / Aerial systems etc: http://www.ajlelectronics.co.uk

ukdave2002 · Joined: 23 Nov 2007 Posts: 4104 Location: South Cheshire

peppiB · Posted: Sat May 10, 2014 9:53 pm Post subject:

Will take it out again tomorrow and check the speakers

Must admit that I am not very good on wiring - and don't know anyone who is Sad

peppiB · Posted: Sun May 11, 2014 3:32 pm Post subject:

Can't immediately find a problem with the wiring. One thought though is that the head unit is for front and rear speakers and I am only using the wiring for the front. Would this make a difference?

V8 Nutter · Joined: 27 Aug 2012 Posts: 587

I don't know much about radios, but one of the speakers on my Caddy failed and this in turn caused the ouput transistor to fail. G.M. radios at this time had a bad reputation the speakers had to have the correct impedence if not the output transistor was the first thing to go. Perhaps Blaupunkts have a similar problem and another speaker could solve it.

peppiB · Posted: Mon May 12, 2014 3:54 pm Post subject:

Hopefully now sorted. radio out, speakers out, multimeter out and then each individual wire traced and attached. It works fine now, gets warm but not hot.
many thanks, especially ajlelectronics and ukdave who pointed me in the direction of the speaker wiring