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day shot to hell

OK, I just got the first board from production this morning, for this spectroscopy controller thing.

ftp://jjlarkin.lmi.net/First.JPG

It gets 12 volts in, which runs an LTM8023 switcher brick to make 3.3 volts. The 3.3 runs most of the logic on the board (including a Spartan 6 and a PLX PCIe bridge, both BGAs) and also drives four secondary switchers and some LDOs to make 1.2, 1.5, 1.8, 2.5, and -5 for various uses.

So when I powered it up everything went nuts. The PLX chip was obviously fried. After that was pulled, the Xilinx was running hot, and the 3.3 volt supply was bogged down to about 2.6. The LTM regulator was hot.

Pulled the Spartan BGA next.

Now the 3.3 volt rail wants to run at 5 or so.

After much head scratching, I discovered this:

ftp://jjlarkin.lmi.net/Swapped.jpg

The resistor that's screened "R127" is actually R129. And vice versa. So the switcher was programmed wrong, told to run at an absurdly low frequency and an absurdly high voltage. The ref designators somehow got misplaced during layout. We usually check for this.

Apparently our production people, when semi-auto placing dense parts, double-check the ref designator and plop the part into the "correct" place, even if the machine coordinates are a little off. I'll have to warn them to be suspicious about cases like this, especially on first articles.

TGIF

John

Reply to
John Larkin
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Better complain to the head of Engineering. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
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ElectroOptical Innovations
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Reply to
Phil Hobbs

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Yea, know the feeling. Most people I've talked to agree that the first board always has some sort of problem(s).

Cheers

Reply to
Martin Riddle

Hi John and all,

This is a good example of what Jim was talking about.

Inside Thunderbird, I click these links and up pops up I.E.

I have checked Thunderbird for what it wants to call for ftp links.

I do not find any config settings for this.

Does anyone know how to re-configure Thunderbird to call Firefox instead.

Thanks

don

Reply to
don

I (cough!) think most of us have had that happen...

What's the big yellow silkscreened square around the oscillator-in-a-can for? Metal shield maybe?

---Joel

Reply to
Joel Koltner

Hey John, you wasted lots of real estate there. Wish I could have some of that. Doing an EMC fix on a client design right now and I can't even shove one more 0402 part in there :-(

My Thunderbird does not do that, never did. Check Windows for preferences, IOW which program a certain file suffix launches. If no dice: Best may be to hose it all off your computer and do a clean slate install of Firefox and if that doesn't do the trick, Thunderbird as well. But save the bookmarks, email, addresses and whatever else you need.

--
Regards, Joerg

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Reply to
Joerg

Mine were usually followed by ... phut ... *PHOOMP*

It's probably the no-step area, per ISO-9000 :-)

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Regards, Joerg

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Reply to
Joerg

I'm thinking that it would be prudent to clamp or crowbar all the supplies so that silly regulator problems don't take out expensive chips. Transzorbs don't work at low voltages, and real SCR crowbars would be a PITA.

I was thinking about a string of power diodes

+---- +3.3 | | --- \\ / --- | +---- +2.5 | | --- \\ / --- | + | | --- \\ / --- | | |/| +--------------| |----- +1.8 | |\\| +---- +1.5 | | --- \\ / --- | +---- +1.2 | | --- \\ / --- | + | | --- \\ / --- | gnd

using something like S3DB's and maybe some strategically-placed schottkies.

One can also make a pseudo-zener from a bandgap and a bipolar power transistor, which would take more parts but be more accurate.

Or maybe really crowbar the 3.3 volt rail with an SCR that's fired if any of the switchers go nuts.

John

Reply to
John Larkin

Make an SCR crowbar with a TL431 pulling the trigger. I did a design where a >$10k laser is connected to it. The LV rail needed super protection because it could somehow cause the laser to commit suicide. They wanted it to kick in between 3.6V and 3.7V. Built it here in the lab, shipped it to them. So they fired it up, cranked that rather large supply ... 3.63V ... 3.64V ... 3.65V ... *TUNGGG* ... they were impressed.

--
Regards, Joerg

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Reply to
Joerg

I usually produce an "assembly drawing" where another layer of text contains the refdes inside the part outline. This refdes text is defined at the library level and is never moved by hand except when the component moves. This drawing is produced separately from the silkscreen and is shipped to the assembly house. This is the reference, not the silkscreen.

Reply to
a7yvm109gf5d1

Typically this is done via the XYRS file which feeds into the placement machine. So theoretically all this could not possibly have happened, but ... then there's reality. On my last one they had one chip 180 degrees rotated. On all boards :-(

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Regards, Joerg

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Reply to
Joerg

There will be an aluminum cover over the OCXO, more to keep air currents off of it than as an EMI shield. That yellow thing was supposed to be bare copper, not screened, but it is kind of cute this way. The cover will get grounded by the mounting hardware anyhow.

It's impressive how nice of a phase noise improvement you can get by keeping air flow off XOs, even cheap ones. Ditto reducing 1/f noise in opamps.

We've found a few mistakes on this board so far... luckily none are fatal and none require serious kluges. Mostly minor mechanical things that annoy manufacturing.

I didn't ground HSWP_EN on the FPGA (we used it as a signal pin) so all the lines that drive the many TTL interface chips float until the FPGA is configured. Some of them randomly go linear and get quite hot (fun to watch on the FLIR) and almost bog down the 3.3 volt switcher. Luckily I can pull down HSWP with a resistor, which adds weak pullups at powerup time, fixing that problem.

I will breathe serious sighs of relief when the PCIe link works and the FPGA configures.

John

Reply to
John Larkin

We have lots of space for this one. We're replacing an older-generation board that is about 6x or so of our board area.

You will be not-pleased to know that the switcher section has its own rectangular ground plane section that is connected to the rest of the plane through a number of thinnish slivers. The rows of inductors, incoming and outgoing, straddle the plane gaps. The idea is to keep the various circulating currents in the switchers from leaking into the main ground plane where the analog stuff is. I did the spread-spectrum thing on all the switchers, too.

John

Reply to
John Larkin

Interestingly, one of the line items in my recommendations for this one is to pepper a similar isolated plane with vias to the ground plane. For EMC purposes, since this one must pass much stricter rules than the usual class B.

Oh, how I wish I could do spread spectrum. But with the EMC measures so far I am already at a full 100% of available real estate. Unless someone knows a self-contained oscillator in an SC75 package :-)

--
Regards, Joerg

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Reply to
Joerg

Our automatic insertion tools would never make this mistake. They make a *lot* of others, but not this one. :-(

Fire the manufacturing manager. ;-)

Reply to
krw

We now back-annotate the placement information into the schematic and use Crapture to generate a BOM with placement information. This is released to manufacturing via an ECO and sucked into the pick-n-place machine. The layout guy does produce an "assembly drawing" but it's only use is in inspection. When the two disagree the released BOM is "right". Only engineering can change the BOM, via another ECO) if there is a disagreement. Well, that's the process, anyway.

Reply to
krw

I assume The Brat can kiss her Christmas invitation goodbye this year :-)

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                     "If it doesn\'t fit, use a bigger hammer!"
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Reply to
Nico Coesel

Experience has taught me to power up new boards on a bench psu by winding up the voltage from zero while monitoring the supply rails and input current.

Reply to
Raveninghorde

That often doesn't not help. Many switcher do nothing intil the UVLO threshold is exceeded, and then they step on it with gusto. You may not have enough time to rip out the banana plug before phssseee ... *POOF*

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Regards, Joerg

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Reply to
Joerg

With switchers this rarely does anything and often makes things even worse.

Reply to
krw

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