Any car audio gurus around? "Radio start" circuit.

[Kevin B.]

Question - what is the purpose of the "Radio Start" circuit that cuts power to the radio while you have the key turned to Start? Is that just to make more amps available for the starter, or does it protect the radio from getting zapped or something?

Reason for the question - my radio unit has been cutting out intermittently. I'm pretty sure that I've ruled out wiring, by the expedient of waiting until the radio cuts out and then wiggletesting the harness behind the radio and behind the fuse box. In looking at the fuse box, I have two fuses Radio Main and Radio Start. Both are good, I replaced them to be sure and didn't see a difference. However, and it'll take another couple days until I'm sure, but it appears that the radio stops cutting out intermittently while I have that Radio Start fuse pulled. So now I'm wondering if I can just leave that fuse pulled with no real consequence, or if I need to leave the radio disconnected while I find a wiring diagram and trace that Radio Start circuit and find out what's wrong with it.

 

[I Lean]

I'm watching to learn.

My initial guess would be it provides power to the radio DURING start, when normal switched power goes "off". Maybe?

 

[TurboMinivan]

Well, on my Yaesu ham radios (which are to be wired directly to the battery, and thus are 'hot' at all times) the instruction manual specifically says not to turn on the radio until after the engine is started. It says this will prevent the radio from receiving a voltage spike that can occur when the alternator first engages, thus saving the electronics from potential harm. Perhaps this is the reason?

That's all I got.

 

[DaveB]

Starting your car puts a huge drain on the battery and the voltage drops, also the starter motor is an inductive load and when it shuts off you can get voltage spikes. The alternator also takes a bit to kick on and regulate properly. The electronics in most radios don't take much current so the drain is minimal while starting but the voltage spikes can damage the circuits.

 

[Kevin B.]

Starting your car puts a huge drain on the battery and the voltage drops, also the starter motor is an inductive load and when it shuts off you can get voltage spikes. The alternator also takes a bit to kick on and regulate properly. The electronics in most radios don't take much current so the drain is minimal while starting but the voltage spikes can damage the circuits.

Ok, sounds like I'd better not bypass it then. Thanks!

 

[Kevin B.]

So, definitely that radio start circuit. The head unit conked out this morning, I pulled over and pulled that fuse (engine running), it came right back to life.

Now to find a wiring diagram. This is proving harder than expected. Anyone have access to one that could maybe print me off this circuit in exchange for tasty beverages?