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PTW repairmen: Be aware of electrostatic discharge (ESD)

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Old February 6th, 2008, 17:50   #1
MadMax
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PTW repairmen: Be aware of electrostatic discharge (ESD)

I note that there is almost no discussion regarding ElectroStatic Discharge (ESD) precautions amongst PTW repairmen.

The rubber gloves SystemA supplies with SCKs and Version Up kits are not effective ESD protection. ESD damage is a new problem for AEG mechanics. Up until now, our analogue TM AEGs have been impervious to ESD damage, but SystemA's use of microprocessors brings new issues for us to deal with.

Fortunately these issues are not new to the electronics industry. There are lots of established ways to handle ES buildup. In the eighties, Apple released this video describing ESD:

YouTube - The Shocking Truth

ESD protection is required for the safe handling of electronics components that contain semiconductors (transistors, ICs, etc). Very high voltages can collect on assembly technicians clothes when they move around especially if they wear certain combinations of clothing materials. For example, wearing a cotton t-shirt under a polyester sweater can develop very high static voltages. This phenomenon can be illustrated when one takes off a polyester sweater which can generate sparks which jump between the sweater and the undershirt or between a finger and a grounded device like a computer case.

These sparks reach a very high voltage (exceeding 2,000v!) which can destroy semiconductor components so measures must be taken to safely handle semiconductor assemblies. Small buildups reaching 50v are unnoticable, but they can still cook fine circuit paths in integrated circuits.

Semiconductor components should be stored and shipped in ESD protective bins and packaging:

ESD bins for storage on assembly line
http://www.correctproducts.com/PRODU.../ESD_Bins.html

ESD bags for shipping
http://www.correctproducts.com/PRODU.../ESD_Bags.html

To prevent ESD damage during assembly or repair of your PTWs, your technician must have an ESD grounding station. ESD stations dissapate electrostatic buildups by physically connecting workers and work tables to earth ground. This can be accomplished by wearing grounded ESD wristbands or heel straps.

Heel strap grounding worker to grounded floor surface (special carpet or floor mat that is slightly conductive and grounded)
http://www.correctproducts.com/PRODU...Grounders.html
http://www.correctproducts.com/PRODU.../786-0203.html

Wrist strap connecting wrist to grounded work mat (easier solution to implement)
http://www.correctproducts.com/PRODU...ords/2209.html
http://www.correctproducts.com/PRODU.../RM08-244.html

*easy measure for PTW repairmen to implement*
For those who do not have purpose built ESD protection, I suggest the following:

Connect alligator clips to one end of two 4' lowish gauge flexible wires (stranded 18GA or less). Bare the unclipped ends and screw them down to something that's grounded (say a handy computer case).

Clip one to your watch strap so the clip is touching your wrist. Touch the other to your PTW before you begin disassembling it. Try to hit some place in the mag well where there's a spot where your paint has worn off as you want to hit bare metal instead of a chunk of insulative coating.
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Last edited by MadMax; February 8th, 2008 at 12:56..
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Old February 6th, 2008, 18:11   #2
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Old February 6th, 2008, 18:16   #3
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Scuse the ignorance, but you're not at risk of ruining your PTW from simply operating it, or splitting the receiver, correct?
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Old February 6th, 2008, 18:23   #4
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Just don't touch electronics while battery is plugged in.
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Old February 6th, 2008, 18:37   #5
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Quote:
Originally Posted by LeapingLizard View Post
Just don't touch electronics while battery is plugged in.
Correction, just don't touch the electronics at ALL, without proper ESD procedures.
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Old February 6th, 2008, 18:38   #6
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Quote:
Originally Posted by Styrak View Post
Correction, just don't touch the electronics at ALL, without proper ESD procedures.
Fuck, so if I have to take a look at some connections, I'd have to be properly protected? ><
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Old February 6th, 2008, 18:41   #7
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Quote:
Originally Posted by kos View Post
Fuck, so if I have to take a look at some connections, I'd have to be properly protected? ><
It would be best. You remember all those (I think?) EL-001 or EL-003 parts that always crapped out? They're PCB boards right? Probably ESD 50% of the time or more.
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Old February 6th, 2008, 18:47   #8
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Quote:
Originally Posted by kos View Post
Fuck, so if I have to take a look at some connections, I'd have to be properly protected? ><
BODY CONDOM...
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Old February 6th, 2008, 18:54   #9
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Quote:
Originally Posted by Styrak View Post
It would be best. You remember all those (I think?) EL-001 or EL-003 parts that always crapped out? They're PCB boards right? Probably ESD 50% of the time or more.
Thank god for those '08s then...

Shit, this stuff scares the hell outta me.
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Old February 6th, 2008, 18:55   #10
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Try not to touch any metal connections unnecessarily. There are some ad hoc measures you can take to reduce ESD problems. Touching the metal body isn't an issue as it's a big heavy hunk of metal which would shunt all of the current flow through the body. The real risk is to apply an ESD voltage to an isolated point in the circuit so current blasts through a weak path to ground.

You could implement a poor mans ESD wrist strap by connecting a wire to a metal watch strap or even the buckle as long as it's in contact with your wrist. Connect the other end to something grounded like your computer case.

Grounding your PTW's metal body will put your body's voltage potential at the same ground plane (same voltage) as your PTW electronics. This is a safe condition to start working on your electronics.

Momentarily touching a grounded object will bring your body potential to ground, but further movement can accumulate static charge which is why a wrist strap is a better solution to continuously dissapate static charges.

Dissapating ESD can be done without much special equipment if you can adhere to a rigid procedure:

1. ground yourself (wrist strap)
2. ground the body of whatever you're working on

Not wearing particularly bad combinations of clothing can reduce rapid static buildup (e.g. fleece sweater and a cotton shirt). Dry winter air is not very conductive. Because of this ESD can build to higher voltages before either breaking down the air (spark) or gradually dissapating through slower ion transfer.
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Old February 6th, 2008, 19:06   #11
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Quote:
Originally Posted by Styrak View Post
It would be best. You remember all those (I think?) EL-001 or EL-003 parts that always crapped out? They're PCB boards right? Probably ESD 50% of the time or more.
Not always unfortunately. I suspect that some EL-003 switch modules might be getting cooked when users fire their PTWs on a low battery. The EL-003 switch module is a bank of MOSFETs which can act as a resistor if they do not receive a full "on" signal. When this occurs they can end up dissapating a lot of heat and burn out.

If your PTW starts to slow down, do not continue to fire until the battery is kaput. You could be heating up your FET bank. Unfortunately I haven't had the time to confirm this with direct measurement. It's just a reasonable conjecture at this point.
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Old February 6th, 2008, 19:10   #12
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Quote:
Originally Posted by MadMax View Post
Not always unfortunately. I suspect that some EL-003 switch modules might be getting cooked when users fire their PTWs on a low battery. The EL-003 switch module is a bank of MOSFETs which can act as a resistor if they do not receive a full "on" signal. When this occurs they can end up dissapating a lot of heat and burn out.

If your PTW starts to slow down, do not continue to fire until the battery is kaput. You could be heating up your FET bank. Unfortunately I haven't had the time to confirm this with direct measurement. It's just a reasonable conjecture at this point.
Well I was just guessin'. :P
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Old February 6th, 2008, 19:15   #13
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Thanks Carl. Really had me sweating for a while
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Old February 6th, 2008, 20:07   #14
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Great, gonna have to have an ESD strap at home AND at work!

To give some perspective to the ESD thing, know when yo uare walking around when it's dry out and you touch a doorknob and get a shock? That's between 5,000 and 7,000 VOLTS. Not that you'd know it though. Under 2,000V is unfelt by you, but it's very destructive to semiconductors, and you'll never know it happened unless you replace the part itself (after much troubleshooting eliminating all possible causes).

I forget the number of volts, but when I took my refresher Surface Mount Technology soldering course in 2005, the instructor made a point of spending half an hour on ESD, and testing various things we had access to. Know that simply pulling a couple inches of Scotch tape off the roll produces an ESD of up to 1,000V? Neat, eh?
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Old February 6th, 2008, 20:13   #15
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Can I just do it naked?
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