Radio (not VHF) problems

[jonathankent]

I had changed my radio in the car about 12 months ago and have had the older one in the cupboard ever since, so I now thought why not put it in the boat - not as straight forward as I had hoped, but hopefully someone here will be able to put me right again.

I had to check whether I had the security code so went to connect it to a 12v battery yesterday, using the correct pins on the radio (pic below) to switch it on... blew the 10a fuse almost straight away. OK, I'll go back and try and connect it back into the car (maybe straight on a battery was a mistake), yet exactly the same happened - blew the fuse as soon as the power touched the pin.

Where could I be going wrong... the radio worked fine when in the car, and all its done is sit in the cupboard for 12 months. The pic below shows the wiring diagram for the audio system in the car.

Now, this is maybe where I have made an incorrect assumption.... when the top diagram shows pin 8 going to earth, I connected this to the -ve side of the battery... is this correct?? the second diagram doesn't quite show the earth as going to the -ve side of the battery.

What else could be wrong with it??
What would have happened if the +ve and -ve were connected the wrong way around??
What can I look for / test to try and find the root cause of the problem??

Your guidance would be much appreciated.

Jonathan

 

[steverow]

OK I think you have probably short circuited the protection diode.
This will happen if you inadvertantly connect the device the wrong way round.
As the diode is now SC it will always blow the fuse.
You need to whip the cover off and look close to the power cable input for a small rectifier type diode. It will probably look like a little black plastic bead with a stripe at one end. Make sure it is connected across the pos and neg first.
This needs to be desoldered and then checked with a multimeter on resistance scale.
Connect the diode across the multimeter first one way round then the other.
If you get a reading both ways then it is SC.
A good diode should only read resistance one way only.
Maplin will be able to supply you a new one.
Something like an 1N1004 will suffice.


Steve.

 

[William_H]

If you8find the diode then I suggest rather than desolder it cut carefully about mid way along one wire test the diode and if it is OK then carflly resolder the two ends. It should be quite simple to make your radio work. If Iwas you however I would find an old manually tuned radio so you don't have to provide memory current which in my experience is significant in long term on a small battery. Note that the memory voltage should be connected before the main power (from Acc circuit) but I don't know if failure to do so will matter. You can just common the memory +ve to power positive in the boat but you will have to retune each time you use the radio. olewill

 

[jonathankent]

Thanks Steve - sounds about right. I'm not that knowledgable with the electronics/circuitry, all I did was have a look and see if anything looked blown, i.e. black.
I will have a look tonight.
Thanks, Jonathan.

 

[jonathankent]

Looks like I have made a mistake with the +ve and -ve, the diagram is a mirror image of the radio, i.e. the connector and not the plug /forums/images/graemlins/shocked.gif well, at least I know more or less what I have done.

Now I have had a look... found what I believe to be the diode (black, with a silver/white strip at one end) and looks to be connected with the +ve and -ve on the separate board, well looks like it is all connected to each other and the fuse.

Now... on the what I believe is the diode, it says VON and RL202. Now I have done a quick search on Maplin and come up with nothing. Is this in actual fact the diode or something else?? I have had a look at the rectifier diodes and found one that operates at 2A and has a maximum peak current of 50A link here. Am I on the right track??

 

[William_H]

If it is only an old radio and you promise never to connect power in reverse again then just cut one leg and don't replace it. Even if you want to replace it you will at least prove that this is the problem. Yes that diode will probably do.
The easiest trick is to use the metal case as negative then connect the negative wire to it, you can't go too far wrong then. olewill

 

[jonathankent]

So if the diode is taken out of the circuit, that will stop the fuse blowing instantly??

How is the circuit complete if the negative goes straight to the metal case and not back to the battery??

 

[jonathankent]

Took out the diode and it now works OK. I think I will replace the diode though anyway - don't want to risk it again.

Cheers, Jonathan