Transient Electrical Discharge (TED): A Destructive Mystery

[chris23892]

Greetings all! First time posting and do I have a mystery I could use some insight on. I managing a Technical case where my Company has Tablets installed on forklifts. All the computer tablets have been installed and I'm starting to see Tablets come back into Service.

I take a peek at the Motherboard and each one has some pretty extreme electrical damage. We included a full system; Wire harness (fused, instructions, hardware) mounting for the Tablet and a power adapter. I've rulled out any design flaws in the system- We have been using this on forklifts for over two years.

This install base is different. The quntity of returns with these detroyed componets are growing. I know what the componets are, where it's (whatever the source of the spike) is coming in our system. I just don't know WHERE the source is coming from.
I've included the most common place on the PCB board (taken through a microscope) of a EMI protection componet. Tracing this componet and others damaged in this circuit path lead me to common grounds on the Motherboard.

Again, this in installed on a forklift. This type of damage I've before:
- Lightning
- Transient Electrical Discharge caused by static build up.

The power system is only 19 VCD to power the tablet. This damage was done very fast- The ATC 10A fuse on the power adapter is not blown (but I still see power adapters come in damaged- either the adapter is an open or a full short internally). The Motherboard, the internal fuses are OK, but I've seen some EXTREME damage to some Zener and in line bloking Diodes.

Yes, this damage was done fast with a very high enegy output.

I'm planning a trip to the site. This looks like an issue with grounding. Either the installs were not grounded correctly or maybe the lifts aren't grounded (most forklifts have chains that touch the ground to prevent static buld up.

Any suggestions on what to look for?
My game plan is to test all the grounds, make sure everything has a common ground and see if there's any potensial between grounds. I'll be using my Fluke meter with data logger and my fluke o-scope (200mHZ). Goal with the o-scope is take a peek on power and ground lines and make use of the Spectrum analyzer function (it's just running a FFT on the o-scope input) to see if there's any higher freq spikes that may be adding up. May have a harmonic that rided on the DC line causing a massive spike on the DC offset very quickly. I want to also look at the install to ensure everything is OK

What are some thoughts?
Thanks and really look forward to this disscussion!

 

[waross]

Is there any equipment installed on these forklifts that may cause greater than normal load dumps? The removal of a heavy load (load dump) from an automotive type alternator may cause a transient of over 100 VDC before the voltage regulator can respond and before the rotating field can collapse. Are any of your inputs tied to the fork lift electrical system so as to be susceptible to load dump voltages?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[chris23892]

Good question and good point. Don't know, I haven't seen the installs. I will be seeing them here soon, so that's a great thing for me to check. The CLient had an install Team istall our equipment. I don't know how the tied ground, where they got Voltage or anything. I'm trying to formulate a game plan for the visit that could provide me with data for RCA on why I'm seeing this type of damage.


Great input!

Here's another failure as seen through the Microscope.

 

[IRstuff]

I think it's neither lightning nor TED, since the damage level appears to be somewhere inbetween. Lightning would have vaporized the entire board; TED generally would only show microscopic damage that requires opening the chip package and inspecting the integrated circuit within.

The level of damage is consistent with Bill's hypothesis. I've blown chips of that size with connections of hot chassis's to real grounds. If that chip is supposedly an "EMI" component, then it's woefully inadequate for protection against vehicle power. Vehicle power is generally so unclean that there is a MIL-STD just to delineate the minimum requirements needed to protect against it.

TTFN
faq731-376

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[DRWeig]

I've seen damage of that level from the back-emf when solenoids, relay coils, or transformer secondaries are switched off with no protection installed. A good-size solenoid can throw several hundred volts back down the line when its coil is switched off. The usual components on a vehicle either don't care or else they come with protection in the form of a shunt diode.

Best to you,

Goober Dave

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[VEBill]

"Load dump", "alternator"

Are these electric (battery powered) forklifts? Or do they have an engine (e.g. propane fuelled)?

 

[chris23892]

Pretty sure they are propane lifts.

So, we rule out lightning (which I did because these are installed in warehouses) and TED is still questionable. What tests should I be looking into to verify the Load dump hypothisis?

 

[IRstuff]

Unless you have Tesla coil or van de Graff generators roaming aimlessly around in the warehouse, the human generated TED would only amount to about a millijoule, which is too low to vaporize copper. Moreover, the damage is highly localized, and could only be produced by human discharge if they had physical access to the board and were able to poke their finger, after vigorous carpet rubbing, at the lead.

TTFN
faq731-376

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[Noway2]

Those look like decoupling capacitors on the power supply. My initial thought was that you have some non isolated IO that is referenced to the power supply on your system making "real world" contact. From the picture, the brunt of the damage actually looks to be at the via, which I assume is +V and ground, which to me would suggest that something caused the voltage to rise, but that the path is not an overload through the power supply. In terms of speed, if for example, a 3.3V IO circuit were to come in contact with a battery terminal that is referenced to the same ground, the speed of destruction would be almost instant. I would look very closely at the goes-intas and goes-outas of that circuit board especially if it is connected to that supply voltage.

 

[zappedagain]

What are your components with the 'B#" reference designator? The way the one smoked in Picture_182 looks like a tantalum cap that had a reverse bias applied across it; you don't need much voltage at all to do that. I'm agreeing with Noway2.

Z

 

[Comcokid]

The first picture 178.jpg looks a little strange. The damaged package appears to be a SOT23-6pin device which is not typically a high-power type package that would be associated with a protection device of incomming power. Not only that, it's the corner of the plastic package and corner pin of the package that show excessive heat damage. Damage to the chip inside a package would usually fracture the center of the package. This damage appears to be more like a foreign object inside the case shorting out to the pin of the IC. By the time you got the unit back the offending item (piece of wire, screw, ??) was somewhere else in the case.

The second picture 182.jpg appears to be damage to a ceramic capacitor next to what appears to be a flex-circuit connector. There appears to be a burn connection inside the connector. This suggests a LCD display (or keyboard?) that got a severe static zap, or discharge to the outside of the case next to the display that then traveled either into the display or into the flex cable of the display into the main PCB. Static damage to items exposed on the outside of the case (displays, keyboards, I/O ports) is more typical of expected damage.

 

[chris23892]

What we are looking at here is an I/O interface for power, USB, rs232 all that good stuff. None of this is power. All these pics are from the EMI protection. the other pic id the actual connector to the I/O. Yes, this damage jumped on both sides of the board. when I trace the paths down in the schematics, the all lead to the system ground.

 

[mikekilroy]

u asked for ideas how to diagnose when u get on site. take a PEAK READING DC VOLTMETER. drive around with the normal divers for a while.... turn machine on/off many times....

I could only see ONE pix; a small 6 pin IC so no idea what the 'caps damage' stuff is about.

It sure sounds like you will find voltage spikes that are doing the damage.

If batts and not propane, then might be BackEMF from the motors when they decel - I have watched some of the fork lift drives SLIDE their machines across the floor with such maneuvers.

If propane, then chance it is un-suppressed DC solenoids and coils in the machine. I destroyed many transistors before finding a single un-suppresed relay in a machine: simple 1N4004 diode across it fixed it for life.

You will see LOTS of Chevy pickups and SUVs of 2000-ish vintage on the street with only 1 front parking lite lit: un supressed coils killed the filaments for YEARS before GM figured out that on turning off the stupid ignition, coils turned off causing hundreds of volt spikes into those daytime running lites..... I tried to tell them but they would not listen

 

[Skogsgurra]

Not enough energy in an ignition coil to kill a car light. Not even a parking light. And, if it kills one, the next one will die soon after because then there is twice the resistance in circuit.

A load dump could kill lights. But you do not disconnect the battery while running? Do you? Or is there some master DC switch that opens before emgine is turned off?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[mikekilroy]

Guess I never considered the ignition coil being the cause of the outlites; I always assumed it was un-suppressed coils like relays, Ac clutch, or some other similar device. I don't know when the lites failed so may not have been at turn off all the time... I do know that for 3 years my Chevy Tahoe blew a parking lite regularly, then for the next 3 years after I put 1n4004 diodes across each it never happened again....

 

[Skogsgurra]

No, you didn't. I misread this: "turning off the stupid ignition, coils turned off" Didn't see the comma.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.