CurtPalme.com Home Theater Forum

**Curt Palme**

..no, it's not a new drink with a snack, but hey, feel free to steal the name.. Wink

Dragan and I just exchanged some emails regarding CMOS chips and their susceptibility to static electricity.

I was told in college (1981-1983) that once installed on a PC board, the chance of nuking a CMOS chip went to zero, as the surrounding components on the PC board would shunt any static electricity charges equally either to ground or to all other pins, and the input gates wouldn't blow.

It's really only loose uninstalled chips that are sensitive to static.

In the 30+ years of building stuff and repairing equipment, I've blown my share of chips, but never due to static electricity. (at least that I could figure).

Dragan said that he was given crap on a forum for posting a pix of a CLM daughter board on a carpet. I say that's not a great practice, but again, the chips won't blow.

What says the rest of you?

**AnalogRocks** · Posted: Mon Jan 04, 2010 5:09 am Post subject:

I wouldn't transport a circuit board in the dead of winter with sock feet on carpet with out a static bag but I can tell you I've had video cards, SCSI cards, DVD cards, Parallel/serial cards and mother boards laying around bare with no anti-static bags on them and they work fine years later.

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

It's true it was I, the one who put his new longbow Vim and a pillow for picture. Soon after i was having a problem not being able to control brightness or contrast with the green on my one longbow. I figured out it was the Ad835 chip. But i did not realize it was static electricity that may have zapped it till a few months later when i reposted the pic of my vim for another thread. TSE chimed it that its not smart to put bare boards on a cloth surface due to ESD damage possibilities. thats when it clicked , that ESD must have damaged my new longbows AD835 on the Vim.

Now it may have been a coincidence but it worked before and then after the photo shoot it didn't.
Now i am very careful of putting Boards down on any cloth surface or touching my clothing while i work on them.

use ESD bags dragan, or do what Digikey, mouser and newark does, paper.

Athanasios

**Curt Palme** · Posted: Mon Jan 04, 2010 2:00 pm Post subject:

OK, think about the static this way:

Static electricity can reach 1000s of volts, thus in a dark room you can see the arc to a doorknob or whatnot. The current is insanely low which is why you don't get killed.

Now, think of your body as being charged positively, and the chip is negative. Touch a chip pin, and you can kill an input gate that is indeed static sensitive on a CMOS chip.

The pin you touch get zapped, the other pins might be OK.

Now, put that chip in a circuit, and considering that each pin has an input impedance in the 10s of megohms, the circuit around the chips more or less shorts all pints together, as the resistance between pins becomes in the K ohms, not the 10s of megohms.

Each pin is now more or less at the same potential, and if a static charge hits the board, all pins now get the same equal charge, and since each pin is at the same voltage potential, whether at 0 volts or 100,000 volts, there is no path for the static charge to flow, and therefore the chip doesn't blow.

joatmon · Joined: 17 Mar 2009 Posts: 127 Location: Ottawa, Ontario

I work with electronics boards that have a msrp in the 100,000's... we take it (ESD) quite seriously... need I say more? Smile

**Curt Palme** · Posted: Mon Jan 04, 2010 3:48 pm Post subject:

That's my point though. All the manufacturers take ESD very seriously. I worked at Mitel in a work experience program back in 1983 for 2 weeks, so I've seen it too.

Is it necessary though... once the chips are installed on a PC board? During assembly, no question that it is.

I'm wondering if anyone has any stats doing repair work with and without things like wrist straps...

Heck, consider the really old Gretag IMage Systems Aquaray, that has CPU chips inches away from 34,000 volts. The set failed often, but that was due to construction usually and not due to CMOS chip failure.

Tim in Phoenix · Joined: 21 Oct 2006 Posts: 4409 Location: Phoenix

Guys!

Static was taken very seriously at Electrohome; handling boards without a wrist grounding strap was a hanging offense. It might not blow a chip but was thought to weaken chips and cause early failure in the field.

.

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

well interesting info that's for sure. What curt say's makes sense but Athan's story is particularly so because it was like worked- put on cloth pillow- didn't work. Confused

I had a CLM sent to me from a presumably working machine that arrived totally dead. Then, an Ultra FGM that was working but developed a problem in the geometry section,which I don't even work on and isn't part of the HD mod's package? In both cases there were iether peanuts or bubble wrap for shipping with no ESD protection. It's only 2 cases in probly over 100 boards but it's still annoying.
I think I'll have to ask Kal to add some ESD instructions to the PDF file, especially for CLM and FGM/FCM boards. Better safe and aggravated

tse · Joined: 03 May 2006 Posts: 1014 Location: Sweatbucket, Fl.

**Curt Palme** · Posted: Tue Jan 05, 2010 3:05 am Post subject:

All good points guys! I neglected to consider that the amounts of static change from location to location. That's also what I was taught in college, ground straps, etc, and I can't remember where I was told that installed chips are not susceptible to damage.

Once I see Dragan's FGM, I'll see what the problem is, but I'll bet it's not a problem with a blown CMOS chip.

zGman · Joined: 22 May 2006 Posts: 599

Well - my 2 cents -

I look at whether I can afford to lose something, whether it is a board I have spares for or not....

Sure, we all get away with poor shop practices, but just the time you really need something to work,
Murphy's law will kick in and bite the @ss....

It may be overkill, but I run good quality surge strips on all electronics in the house, and good UPS's
on all AV and network gear on top of that....after loosing a few nice pieces of gear over the years, I like
peace of mind. I have many boxes of PJ parts, the ones that are tested good are all in antistatic
bags or antistatic foam wrap - sure Curt or Mike can repair things, but no matter what it will still
cost time and money - not to mention downtime, and potential customer aggravation, etc, etc....

I disagree with the assumption that chips are safe from static discharge when on a circuit board,
that is simply disregarding the time related function of the input pulse & this is a common fallacy
in many forms of engineering education. A structure can fail under a smaller impulse (time vs force)
than it would under a steady applied load, and the same is true for voltage spikes in electronic circuits.

well, maybe that was 3 cents worth.....hohoho!

Merry Christmas and Happy New Year to all....

Best wishes for happy CRT'ing....

G

mp20748 · Posted: Tue Jan 05, 2010 3:10 pm Post subject:

I'm with both Curt and Scott on this...

Unless you live or operate in a really bad environment for static, there's really nothing to worry about with any of the boards in a Marquee concerning static damage.

The only real static/electrical damage I've ever experienced on a Marquee was HV arching, which has took out both HDM and VIM's.

I understand the theory and reason behind static protection, but it's more of a concern for the UN-protected CMOS chip. Once it's populated on a reasonable size board, it's a non-issue... at least that has been my experience.

CMOS chip damage is rarely instantaneous, unless you expose it to blatant static discharge. Once the device is exposed to that small amount of static that could damage it, the chip will usually fail days or even months after the exposure. So it's hard to say when the chip was damaged. And that's why the manufacturers ship the chips in seriously overdone protection packaging. So if the chip does fail, they want to to rule them out.

Me, I have one basic rule with this. Don't touch a CMOS chip before you set down and ground yourself. When it comes to boards. I can't recall the last time I've had a problem with a CMOS chip failing. So this is not an issue for me, especially on the Marquee boards.

In the years that I have been doing mods, I've had a many board shipped to me that were either never tested or were known to not work. In a lot of cases, people used a second set of boards to send in for mods. And in every case, whatever board that did not work, I had to repair or replace. And I did so without ever mentioning it to the customer on most of them.

**Curt Palme** · Posted: Tue Jan 05, 2010 3:17 pm Post subject:

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Well in my house I always get massive static shocks, and in my Theater it is worse. I had to put a bare wire connected to the panel box that comes out to my equipment cabinet to ground my self before I touch my Tv-One units otherwise the LED screen goes blank and I can only recover it if i do a firmware update.

I keep forgetting to mention this to them so that can add some more ESD protection.

I also did blow one of the op amps on the CMM the same way, i saw the spark on the board before I put it in picking it up off the table after I walked across the carpet in the theater, put in the CMM and the green was overtaking everything else, luckily when I order replacement parts i order extra. Now i touch that wire in my cabinet before i touch anything after walking across the carpet, and it doesn't matter what shoes I am wearing. I guess I just am electrifying Wink

Athanasios

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

CIR Engineering · Posted: Tue Jan 05, 2010 9:17 pm Post subject:

There are a lot of great points in this debate, I'll have to go back and read this thread without skimming...

I think the point about location is a good one, but add to that the season. Winter in Chicago, we have tons of static and it's a big problem for me. In the Summer when it gets humid there is no chance of static. When I work in Arizona static is always a problem any time of year, and in Florida static is a non-issue whenever.

My standard ESD test when traveling is using my Accupel HDG-3000 because when the air gets dry enough, I sometimes zap the generator resulting in buggout. The only way to get the 3000 back is with a power cycle. When I talked to Greg Rogers about this years ago he said he never had that problem in Oregon Wink

I receive a lot of boards for repair from clients and I always tell them to ship the boards in ESD bags. Occasionally, I'll get a set that is in a plastic trash bag thrown in with peanuts. I always call the client before working on the boards when this happens to absolve liability before I start. However to date, none of the boards I've gotten this way have been bad. I've also left boards laying around out in the open for years and they still work. But I do feel pretty certain that I have damaged at least a few boards with ESD while handling them which correlates pretty well with Murphy's Law.

craigr

westom · Joined: 14 Dec 2009 Posts: 56

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Here are some products for anti static shipping. I get the U-Line catalog here at work.

http://www.uline.com/cls_21/Anti-Static

Athanasios

HK-Steve · Posted: Sat Jan 09, 2010 9:19 am Post subject:

Great thread, plus lots of good comments.

Also the clothes we wear also are a factor in the amount of static we cary on ourselves,
I wear a lot of lycra sports t-shirts, NO COMMENTS OK Laughing

,

But when I take them off at night with the lights off, there is a lightning show of discharges between me and the t-shirt
Looks really cool, a halo of blue discharges.

I have a good ESD practice in my workshop, plus the use of ESD bags,
I have had no issues, but prevention is better than replacing a damaged board, especially when a lot of time has been spent modifying it or upgrading components.

Cheers
Steve