Strange Factory Sound System Issue

[moeldner]

We recently purchased a 98 Rav4 3D hardtop.

We have an issue with the factory tape deck installed in the car.

It works well, but it loses it's radio presets and time settings when starting the car.

It's not the turning off of the car that does it, but when the key is turned from "on" to "start".

Interestingly, if I turn the key quickly from off to start, the presets aren't lost. It appears to be only from on to start.

I hope this makes sense, and I hope someone can help me out with what may be the problem.

I've been told by someone with limited experience it may be the ignition barrel itself that is the problem. Is this correct?

[bitman]

a radio has 2 power +12v connections.

one comes from the acc / ignition and turns the radio on and off by key.

and one comes direct (via fuse) from the Battery, this is the one you probably miss since it keeps the radio on the power (very small mini amps) so it remembers things.

[Hoovie]

This is an odd one

Bitman - I think if it was as you say then it would lose settings when ignition is off - and moeldner says it is ok when ignition is off, but loses the info when key goes to start position.

But I agree it must be the +12V line which is the problem - question is why on earth should that drop when the key is between position?

Only thing I can think off is when starting the car, maybe the voltage on the permanent +12V line is dropping below the minimum voltage needed to maintain the info - but then there probably wouldn't be enough to actually start the car either.

I am intrigued to know the answer of this one :)

[shcm]

It's not unusual for different bits of electronics on the car to have different minimum operating voltage specifications.

For example, an engine management system will typically be spec'ed for full operation to something like 5.5V to 6V min. Might sound low, but during some cranking conditions, the Battery voltage can be turned into an AC looking waveform by the started motor load and the dips in the waveform can be as low as this. Obviously the EMS has to keep working at this low a voltage, in order to start the car, but, the point is you can still start it.

Might be worth checking the Battery condition. However, I think there is a more likely possibility. The tape deck probably has internally some "reservoir" capacitors in its power supply circuit. These should hold up the voltage internally to the tape desk during brief voltage dips, such as during starting. They will discharge during these periods, but the power supply should be designed to provide the min voltage required to maintain the tape deck "memory", after a specific period. The capacitors are key to this.

In the "off" to "start" case, the initial capacitor voltage will be up at about 12.5V for example, before the voltage dips during starting. In the "on" to "start" case, they Battery voltage may well have dropped to say 12V, due to other electrical loads coming on in the "on" position and pulling the battery voltage down. That slight difference of 0.5V initial capacitor voltage (just an example here), may well be enough to make the difference between loosing the memory and not loosing it.

We used to have a Peugeot in the family, that did just this. Started, but lost its radio security code occasionally.

Could be an early indication of a duff battery, plus, with age/temperature, capacitors can go leaky, which won't help either. Possibly a combination of both.

[moeldner]

The Battery is about 5 years old (and probably due for replacement). The car has come from a location in here in Australia that has temps less than -10 C in Winter, and 40 + C in Summer which doesn't help Battery condition, so I suspect you may be right about the Battery.

With the age of the battery, I was already considering replacing it, maybe I just need to do it sooner rather than later.

Thanks for the advice, I'll post back when I've changed the battery and see if that corrects it.

[bothwell_buyer]

Basically just supporting shcm note.

A 3 door petrol RAV has one of the smallest batteries never fitted to a torch, and only ever fitted to a RAV. If its 5 years old, its done. kaput. Worn out. Deid. Past its recycling date.

Check it by throwing it into a local river/deep pond - if it floats then its ok. If it sinks, then you'll need to buy a new one.

You'll find that a new one will keep the radio settings - you might just find that a 10 year old car has the electronics of a dimwit and the fore-mentioned capacitors are actually back-feeding the Battery to help start the car and give some voltage to the engine management unit - calling it an ecu is a bit optimistic. The elctronics will have been designed nearer 20 years ago as the 3SFE engine (if thats the engine) was on the go in other Toyota cars back in the 1980s.

If unsure, borrow someone elses Battery, hook it up for a day and then go thru the process of starting it and see what happens.

If I'm wrong, you're welcome to throw yer Battery threw my house window here in Northern Siberia!

[shcm]

and the fore-mentioned capacitors are actually back-feeding the battery to help start the car and give some voltage

He's at it again, taking the ****. I hope there's some reverse Battery protection diodes in the way inside the tape/radio, to stop these 3 GigaFarad (?) capacitors helping to start the car.

But, yeah, please try and verify the Battery condition before parting with any cash. Always difficult trying to remote diagnose stuff and this is about as remote as we can get, unless we are talking about spacecraft diagnosis.

[Hoovie]

I would go for the Battery as the likely culprit, but is this is possibility ....?

as the key is turned, something in the barrel is causing the Permenant +12V to ground - I would have thought that if that was the case, it would cause a fuse to blow being a direct short, but just wondering

If you have a DMM with a Min/Max setting, you could set this on the Battery, and then start the car and that will tell you how low the Battery dropped in the process - useful to help diagnose the problem (even without a min/max, you could just watch the meter if you position it in view)

[anchorman]

The radio has 2 feed - one permanent which keeps the memory and one ignition to wake it up (I think that might be shcm's term). You could be losing both but the important one is the permanent feed which is probably nothing to do with the ignition switch. You are right Hoovie if it was going to ground it would short out, this would be going "open circuit" if it was a fault on the switch. It could be a fault with the Battery but a radio would normally work with a nominal terminal voltage. If the Battery can generate enough "cranking" voltage then I would have thought it would keep the memory OK. The real test is with a drop tester and most good spares shops or tyre and Battery centres will have one and do it FOC. I would try that first and then see about running a "hot wire" to the memory connection on the radio just to try it during cranking.

[moeldner]

thanks for the advice - I'll track one down.

[bothwell_buyer]

thanks for the advice - I'll track one down.

Stop wasting yer time - wan o yer neeburs in Aussieland has flung in the turbo enjun intae his RAV and noo re-engineers sand dunes. Live life tae the full.....get rid of the radio and get the 3SGTE engine slotted in an enjoy yersel while ye can still remember things!!!

If you like, I'll come out to Aussieland and fix it for you. Small problem about where to stay tho.