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Interesting that it says to disconnect the positive cable. Seems to me the old rule of disconnecting the negative cable first (with negative ground systems) would be the safest approach. What am I missing here?
 

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Interesting that it says to disconnect the positive cable. Seems to me the old rule of disconnecting the negative cable first (with negative ground systems) would be the safest approach. What am I missing here?
New electronics are extremely sensitive to voltages, and can easily be damaged if you have the positive connection present, but no ground reference. Trust me - I completely know what I am talking about here because of my job and how it deals with electronics.

By the way, this is a great point for all you guys out there who have been disconnecting the negative terminal in your cars for years. It was okay when the electronics were slow and simple years ago, but you take a risk of seriously messing them up if you do it now. Also, just because you did it once before on this new car does not mean you will get by with it again. Think Russian roulette (although electrical overstress in electronics can have a cumulative effect).
 

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And about the negative/positive removal sequence discussion earlier. The reason for doing the negative first, is that if you happen to touch any other 'ground' with the wrench... nothing happens. If you wrench on the positive terminal, and swing wide to touch anything grounded... you're in for (at least) some fireworks!!! Opening the cars 'circuit' at the battery, it shouldn't matter which is removed first... you're just 'breaking' a loop.
Hi Autoxal,

Removing the positive instead of ground does matter for some electronics fabricated in silicon, especially as the miniturization increases and you get further down in utilizing ultra deep submicron technologies. I have not gotten around to writing an exhaustive post of why this is the case, but maybe I will get a chance soon. In the meantime, just let me say the following.

First of all, positive power feeds can have electrical filters on the printed circuit boards which can take care of energy from upstream arcing and sparking propagating down the rails, but, for various reasons, such filters cannot easily be placed on negative. Therefore, designers will normally not go to the difficult lenghts required to correctly put such filters there on negative.

Secondly, different parts of circuits are connected to each other, and if they lose negative they lose their common reference. This can cause momentary potential differences to develop between them, which can result in electrical overstress. Note, we are not talking about large currents here which, of course, will not flow after either terminal has been removed. We also are not talking about long times here (we are talking about MUCH LESS than 1/1000 of a second). Also, we are talking about small charge buildup. CMOS devices can switch extremely fast (thousands of millions of times per second), but to do that requires fabricating them in a way which leaves them extremely sensitive to electrical overstress. It does not take much (or long) for them to fail in various ways, including, for example, gate oxide ruptures if that small charge buildup happens in just the right way.

If the rework instructions from GM says remove positive first, there surely could be great reasons they are indicating this. Don't risk doing otherwise just because you got by with it in the past.
 
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Thanks for the explanation... guess I'm behind the curve on modern electronics. My most exciting 'positive battery side' experience was with my (bought new) '67 Firebird. Still very much a rookie at working on cars, I had a wrench on the positive cable nut on starter motor solenoid... Don't recall my reason for being there after all these years... but I still have the 7/16" combo wrench as a reminder of my mistake. The wrench slipped from my grasp, and bridged the gap between the nut and the frame of the car... was a rather brilliant sparking, and thankfully brief, event. No damage except a little melted spot on the box end of the wrench. Assume there is no grounded metal near the positive terminal of the new Corvette's battery location? Otherwise, use extreme caution when removing, to prevent shorting the positive terminal to ground with the wrench (maybe a non-metallic wrench?).
PS: I've signed up on Helm's 'alert' list, to receive word on when the C7 shop manual will available for purchase. If reading the manual calls for positive cable removal, I would have followed the procedure. I'm not exactly sure, even, where the battery is in back?
Is this the first year that it's been called for? I always removed my 2003's negative first, with no apparent issues (I had the shop manual for it, but don't recall it saying positive first?)

(I just remembered what my reason for being near the starter... I was tightening a header bolt, when it dropped down to the starter. Didn't think battery needed disconnecting to remove a header bolt) My '67 Firebird 400 - my first, of four, new red cars:
67atSunoco1.jpg
 

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That is a beautiful car, autoxal. I love some of those classics!

For your 2003, the electronics would have been much slower then than now, so it was a different animal. A lot has changed in electronics in the last 10 years. Heck, a lot has changed in electronics in the last two years or so.

Yeah, people will have to be careful if it does turn out that Chevy indeed does want us to remove + first. All I was saying is, if that is the case, I do understand that there can be many important reasons for this from the sensitive electronics side.

By the way, I work in R&D for a company in the Silicon Valley. I have blown more sensitive electronics in the lab (in various ways) than I care to mention. :)
 

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Discussion Starter · #6 ·
rdslon01, I'm still struggling with the transition from vacuum tubes to transistors! I curious, what is your education and profession? High tech presumably?

Hi Autoxal,

Removing the positive instead of ground does matter for some electronics fabricated in silicon, especially as the miniturization increases and you get further down in utilizing ultra deep submicron technologies. I have not gotten around to writing an exhaustive post of why this is the case, but maybe I will get a chance soon. In the meantime, just let me say the following.

First of all, positive power feeds can have electrical filters on the printed circuit boards which can take care of energy from upstream arcing and sparking propagating down the rails, but, for various reasons, such filters cannot easily be placed on negative. Therefore, designers will normally not go to the difficult lenghts required to correctly put such filters there on negative.

Secondly, different parts of circuits are connected to each other, and if they lose negative they lose their common reference. This can cause momentary potential differences to develop between them, which can result in electrical overstress. Note, we are not talking about large currents here which, of course, will not flow after either terminal has been removed. We also are not talking about long times here (we are talking about MUCH LESS than 1/1000 of a second). Also, we are talking about small charge buildup. CMOS devices can switch extremely fast (thousands of millions of times per second), but to do that requires fabricating them in a way which leaves them extremely sensitive to electrical overstress. It does not take much (or long) for them to fail in various ways, including, for example, gate oxide ruptures if that small charge buildup happens in just the right way.

If the rework instructions from GM says remove positive first, there surely could be great reasons they are indicating this. Don't risk doing otherwise just because you got by with it in the past.
 

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Thanks you "rdslon01." Thinking about charging a depleted battery, what does this say we should do for the C7 as far as connecting jumper cables, i.e., what are the new four sequential steps please?
 

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Here is the proper sequence for jump starting a C7 directly from the manual
Battery jump_1.jpg
Battery jump_2.jpg
Battery jump_3.jpg
 
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rdslon01, I'm still struggling with the transition from vacuum tubes to transistors! I curious, what is your education and profession? High tech presumably?
I received my Bachelors's degree from the University of Kentucky (UK). I double majored in Electrical Engineering (EE) and Math. By the way, one of my classmates went on to work at Corvette in BG after graduating. I didn't go to work immediately after graduation; I next got my Master's degree in EE (also from UK). Being a glutton for punishment :) , I then went to Ohio State (OSU) and got my Ph.D. in EE (major in Electromagnetism and minors in Controls and also Math). I was recruited by Stanford University Network (SUN) Microsystems directly out of OSU, and I have worked in the Silicon Valley ever since (well, I am at a different company now, but still doing the same type of work).

By the way, I don't have any special knowledge of how the Corvette is designed since I have never seen the schematics. I just know what is commonly done in some other electronics fields. The Corvette designers may (or may not) have done similarly. All I can say is do what the designers indicate because it very well may be intentional and important.
 

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P.S. We are creators of massive computers which we sell to various companies around the world for their businesses. For the boards which go in our systems, we always design them such that the pins in board-to-board connectors have different lengths. The grounds are always made longer so they engage first during insertion, and they are the last to disengage when removing the board. They could safely be designed differently, but it could end up being more complicated downstream. What I indicated above is by far the easiest approach while still keeping down "trouble", and it is what we always do.
 

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Thank you rdslon01 and jsvette, for this is a very helpful, financially useful and informative thread! It sure reverses the order of cable placement and removal many of us have done for decades.
 
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