Radio switched supply

[Mark-H]

The radio on the Bongo goes on and off with the key. It comes on at first click ACC and goes off when you turn off and take the key out. However when cranking the ACC supply is interrupted press so the radio reboots. Could wire it up to a permanent live but then risk leaving it on and flattening a battery.

Anyone know of a pick-up for any ACC triggered +12 that does not get interrupted during cranking? If not will have to add a diode and capacitor to the ACC supply to to radio to bridge the cranking gap.

Has anyone done the capacitor/diode “fix”. Not sure how big a capacitor to add.

[g8dhe]

Radios actually have TWO 12v supplies!
The first is an un-switched supply and is to retain memories and settings, this is NOT affected by the ignition switch, this circuit feeds several items (door locks internal lights etc) the wire colour in the original Mazda loom is Blue/Red and is on the Mazda plug at 2C position, if you have an ISO adaptor fitted then that becomes pin ISO A4.
The second supply is for the main radio operation and is on the Ancillaries Circuit, first position on ignition switch, in the Mazda loom its a Blue wire and the Mazda plug is 2A which via an ISO adaptor appears on ISO A7.

Its not uncommon for people who install new radios to be unaware of this and hence connect the supplies incorrectly either both together or they forget/misunderstand the need for the un-switched supply - hence the reboot as all power is switched off!

[Mark-H]

True, but not in this case.

[g8dhe]

So your saying that the backup supply is OK? The memories are retained ?

[Mark-H]

Yep. Just turns ACC off when cranking so radio turns off then back on so has to reboot. Probably going. To add a capacitor and diode to bridge the gap if it gets too annoying.

[g8dhe]

That sounds like the backup supply is not present at all, that supply is fed directly from the battery not via the ignition switch, its the only the main power that is fed via the ignition switch. The two power feeds are at the top right as you can see one is direct to the battery and the other via the ignition switch.

[Mark-H]

Both supplies are working as designed. Problem is the acc gets interrupted while cranking. The drop in ACC is the signal that tells the radio that it should turn off. Have not managed to find a switched ACC supply that is not interrupted while cranking so will probably just add a capacitor and diode to the acc feed to the radio to bridge the gap.

[g8dhe]

That is correct if you left the ACC powered up the then the switching spikes from the starter motor stand a good chance of doing damage to any electronics which are not specifically designed. The very low current backup supply, the ECU all have additional spike protection, most other circuits are also disconnected during cranking of the starter motor for the same reason.

However the Radio should only just be turned off, not re-booted where you loose the memory settings etc. which is why is sounds like the backup supply isn't connected, loosing the backup supply is what causes a re-boot as opposed to a simple turn off.

[Mark-H]

There in lays the confusion. Reboot is the same as on-off. Reset is when settings are lost. Mine just reboots, ie, turns on and off. It dies not reset.

Plan would be to capacitor bridge the acc supply to just the radio by putting the capacitor after a diode on the wire that only supplies the radio thereby leaving all the other acc supplied circuits working as usual.

Just need to establish the current draw in the acc by the battery to size the capacitor.