M4 noise problem (urgent)

**tsakimak** · 12-11-2010, 06:15 PM

i guess you are right i will talk again directly to short circuit.com to see what he has to say me,i already informed him about my problem and said he has sended my mail to the manufacturer for advice.

**OldSpark** · 12-11-2010, 06:15 PM

Well replied on everything Wayne - especially linking Mickz' thread.

I also like the reply to why it/things run with ground disconnected - namely the multiple ground paths - hence why ground fusing is never used. (Well, almost never).

**tsakimak** · 12-11-2010, 06:21 PM

Originally Posted by OldSpark

Well replied on everything Wayne - especially linking Mickz' thread.

I also like the reply to why it/things run with ground disconnected - namely the multiple ground paths - hence why ground fusing is never used. (Well, almost never).

who said about multiple ground paths?I have one ground cable from M4 to the chassis,and when i took it off it still works,now i am not an expert but i believe a device to work needs two cables one 12volt and one ground.Am i making a mistake here?

**Wayne613** · 12-11-2010, 06:27 PM

Originally Posted by tsakimak

who said about multiple ground paths?I have one ground cable from M4 to the chassis,and when i took it off it still works,now i am not an expert but i believe a device to work needs two cables one 12volt and one ground.Am i making a mistake here?

Don´t read into it. He´s just playing at a bit of fun with me, as I had my grounding lead fused at one point.

He was referring in particular to my response about why your unit was still working when you removed the grounding lead from your first post. ie. it had other grounding paths to follow to continue functioning even after you removed the PSU´s grounding lead.

**tsakimak** · 12-11-2010, 06:29 PM

Originally Posted by Wayne613

Don´t read into it. He´s just playing at a bit of fun with me, as I had my grounding lead fused at one point.

He was referring in particular to my response about why your unit was still working when you removed the grounding lead from your first post. ie. it had other grounding paths to follow to continue functioning even after you removed the PSU´s grounding lead.

ok now i got it

**OldSpark** · 12-11-2010, 06:40 PM

I'm not having fun - it was a typical example of why it is not simply a case of "moving" a fuse from hot to gnd, or even adding a fuse to gnd.

Wayne did have a special case where it may have worked because there was only one path to gnd, but that is only true whilst there is no fault from it (somewhere) to gnd. Plus Wayne already had it fused on the hot side as per normal. (It was one of those "seemed like a good idea" until more is understood....)

But tsakimak, you are contradicting yourself.
You say it has no ground and yet it still works.
Does that mean it does not need a ground - you only need the hot side (+12V)?
Or does i mean there are other ground returns?

You did not have to say anything about multiple ground paths - it is implicit ion your statement.
You will probably find paths through input/output signal cables, chassis mounting etc.
And these are the paths that typically burn out under heavy loads if the main ground is lost.
And then the other devices that those grounds connect to - ie, the next device's PCB tracks to its GND connection etc. (EG - HU to amplifiers; lose amp ground and take out the HU too. Or Hummer with 7 DVD systems - lose engine-body ground and smoke the lot! And (power) fuses will NOT prevent that!)

**tsakimak** · 12-11-2010, 06:51 PM

i think i understand what you are saying,i figured my self the returnigs from other devices but when i did that test nothing was on no usb device not even the vga cable of the touchscreen and the mother board and the m4 was on rubber mug(foot carpet if thats right),thats why i didnt know what is happening on.

to make this clear .....ground connected,ignition connected,12v connected to m4,started the pc,when the main screen appeared took off vga cable and then disconnected ground cable from m4 just to see if the noise continue.And yes the noise continued and also the computer was working.that was what happened

**Wayne613** · 12-11-2010, 08:05 PM

Originally Posted by tsakimak

i think i understand what you are saying,i figured my self the returnigs from other devices but when i did that test nothing was on no usb device not even the vga cable of the touchscreen and the mother board and the m4 was on rubber mug(foot carpet if thats right),thats why i didnt know what is happening on.

to make this clear .....ground connected,ignition connected,12v connected to m4,started the pc,when the main screen appeared took off vga cable and then disconnected ground cable from m4 just to see if the noise continue.And yes the noise continued and also the computer was working.that was what happened

In the same vein as what Oldspark was asking, you did try another grounding point for the PSU, correct?

If it´s getting ground from somewhere else along the circuit this could be another possible reason for the noise. Meaning it wasn´t getting ground even before you disconnected it from that point. Not to mention as Oldspark states, this will cause equipment damage down the line at the very least depending on where it´s getting it from and how.

Just because there´s a bolt into the car´s frame doesn´t necessarily mean it´s a good grounding point. I think you had it on the seatbelt bolt? Many of these are coated to prevent corrosion, others provide significant resistance so another less resistance source will be used if available to the circuit. Easiest way to test would probably be to either find one of the grounding taps used by other devices in the console, or just temporarily hook it to the battery´s negative pole itself with the short PSU´s ground lead.

**tsakimak** · 12-11-2010, 08:31 PM

how is it possible to get ground from another source throught the 12volt cable or the ignition cable ?(this one is connected to the cigarette lighter),i mentioned about the bolt that i did a half meter long cable just to see if there would be an improvement to the noise from the other ground wire (which was 2 meters long).That one the 2 meter cable ground is connected to the chassis clear metal behind the main console which is the cd player and i must say that cd player ground ,bluetooth parrot ground and ground for the pc are all connected to the same screw on the chassis.

**Wayne613** · 12-11-2010, 08:43 PM

Originally Posted by tsakimak

how is it possible to get ground from another source throught the 12volt cable or the ignition cable ?(this one is connected to the cigarette lighter),i mentioned about the bolt that i did a half meter long cable just to see if there would be an improvement to the noise from the other ground wire (which was 2 meters long).That one the 2 meter cable ground is connected to the chassis clear metal behind the main console which is the cd player and i must say that cd player ground ,bluetooth parrot ground and ground for the pc are all connected to the same screw on the chassis.

Ok, so Oldspark was right, your not quite getting this one.

Anything that makes contact with the frame or a grounding source has the potential to be a ground point for the circuit, in this case your motherboard which is connected to the PSU, and anything attached to the motherboard or PSU.

As an example, you disconnect everything except the RCA lines going to your amplifier and 12v+ on the PSU. It can and probably will get ground from the ground leads coming from the amp since the amp has a good ground. This in turn follows the circuitboard´s ground trace giving the motherboard ground, this then becomes the PSU´s ground point through it´s molex connector attached to the motherboard. And so on.

If it´s getting it´s ground this way it will not only lead to damage but can potentially create the noise scenario you´re describing.