Voltage drop during start

[HuD 91gt]

Hello,

 

I purchased a retro sound radio recently. Works great. Kind of.

 

it loses all it's memory after starting. I contact retrosound directly, they figure it's from too much voltage drop during start, or a bad ground.

Tested on an old battery, and new. The following stats are from the new battery.

 

12.2v off.  During start, my constant power wire is showing a drop down to 10.5v. After reading online, this seems normal. Retrosound says the constant is the one which usually causes this issue.

initially I had the radio set, so the switched power was connect to the "on" portion of the ignition. Meaning, my fuel pump runs as well when the radio was on. I didn't have any issues with it set like this. I tested this voltage drop. It's the same as the constant 12v.

When I connected the switched 12v to "acc", meaning I can listen to the radio without my fuel pump buzzing I get a much deeper drop. My voltmeter shows down to 1-3volts.  Is this normal?

It's funny how the change from the accessory wire started this issue. Ymir shouldn't have any effect on the memory of the radio. Anyhow I've forwarded my findings to retrosound and will update as the updates come in.

 

 But I'd still like to know why I get such a large voltage drop on start with all my accesories. I tried a second acc source and it gets the same drop as well.

[Patcon]

Try running a temporary feed line straight to the battery just for the memory power.

Does it still lose memory when starting?

Yes >>> battery / voltage issue

No>>> look for bad / corroded connections in the harness reducing the transmitted voltage

           this would be my suspension for deeper drop when wired to the acc key position

 

worst case, find a good discreet source for memory power and leave it like that

[Captain Obvious]

I haven't looked at all the years, but on everything I've messed with the ACC connection goes dead when the key is in the START position. So it sounds to me that your findings where the ACC line goes pretty much to zero when you hit START is normal. It's probably not going completely to zero because it floats and will be probably be pulled one way or the other by some accessory or other device.

As far as the radio forgetting when you hit START... Are you double dog sure you have the "hot at all times"  and the "hot when you want to listen to the radio" wires from the radio properly identified and not swapped by accident?

[HuD 91gt]

I've tripled checked the wires.  12v constant hot to good old yellow.   Acc power to red wire as required.

When I was fooling around with this this afternoon, I noticed it only loses it's memory when the vehicle is in ACC, for a second or more, THEN started.  If I go from ignition off, to start right away I don't get the memory loss.  I'm guessing something to do with the power on, to off (12v loss when started as Captain Obvious states) back to On is causing an issue.  It may be a radio issue after all. 

 

I will probably run a direct line to the battery as trouble shooting, just in case.  Thanks for the replies.

[Captain Obvious]

Bummer. I was hoping that it was just a simple mistake of swapping the wires to the radio. It's my job to ask.

 

So if the wire that is supposed to be hot at all times IS  in fact hot at all times, then in theory there shouldn't be anything that you could do with the ACC connection that would cause loss of volatile memory. And hence... That's why you're here looking for help.

 

So where are you picking up the hot at all times? And where are you picking up the ground connection? Maybe there are some clues to be had with one of those connections. And when you are measuring your voltages as you change the key positions, are you using the exact same ground point as your reference point for the measurements? There's always the possibility that your ground is floating up, not your high side drooping down.

[HuD 91gt]

For constant 12v, i'm using a light blue wire which the other radio was hooked to.   I'll have to dig up a wiring diagram to see exactly what it is.  As for the ground, I have been using the same ground the radio is hooked to for all testing.  It is grounded to a screw on the cigarette lighter.  Heading out of town for a few days so no more updates for a bit.

 

Retrosound thinks it's a wiring issue.  He's getting me to start from the beginning and connect all wires directly to the battery to test radio operation. I think that's a bit silly as we know it works when all leads get power.  As per the fact the radio turns on and off in ACC.   The issue arrises from ACC to Engine ON.  With the power transfer of On/OFF/ON again.  But i'll do what he says and go from there.   Next on his list is grounds.

[Zed Head]

Pretty sure I've read comments in the past about the 240Z's having a momentary loss of power at the ignition switch, due to its design.  The contacts don't overlap.  Might have been on a Megasquirt forum, or about Megasquirt.  I thought it was SteveJ that said so.  Also thought it was between On and Start, not Acc and On.  It changed in later ignition switches, apparently, I think that the 280Z's don't have the problem.

I wonder if some sort of capacitor or uninterruptable power supply could be used to fix it.  I've noticed that my combo CD player/radio in the garage takes a couple of seconds to die when I cut its power.  It must have something inside that holds some power for a while.

 

Spell check suggests "unintelligible"  for "uninterubtible".

[Zed Head]

A thought - maybe a branch from the Start power wire to the radio would maintain its memory.  It can't draw much.  If it does, you could use a relay.  You could have have Acc, On and Start all wired to the radio power.  Use diodes to prevent backfeed.

Still think a good unit has better power supply control.  Which I think is what you're originally suggesting anyway.

[Captain Obvious]

Good luck with the hunt and if you can't figure it out even with Retrosounds help, let us know.

So what year is it that you're working on? I'll take a look at the wiring diagram, but want to use the right one.

[S30Driver]

If his profile is still accurate, it's a 71 Captain O.

[Captain Obvious]

Thanks Jim, I know the early year info is a little sketchy... Hopefully I've got something for that.

[HuD 91gt]

A capacitor makes sense to me.... The diode talk, that's way over my head. Haha

 

and yes it's a '71.

Edited March 29, 2016 by HuD 91gt