day shot to hell

John Larkin · 2009-11-21T00:22:15+00:00

OK, I just got the first board from production this morning, for thisspectroscopy controller thing.ftp://It gets 12 volts in, which runs an LTM8023 switcher brick to make 3.3volts. The 3.3 runs most of the logic on the board (including aSpartan 6 and a PLX PCIe bridge, both BGAs) and also drives foursecondary switchers and some LDOs to make 1.2, 1.5, 1.8, 2.5, and -5for various uses.So when I powered it up everything went nuts. The PLX chip wasobviously fried. After that was pulled, the Xilinx was running hot,and the 3.3 volt supply was bogged down to about 2.6. The LTMregulator 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://The resistor that's screened "R127" is actually R129. And vice versa.So the switcher was programmed wrong, told to run at an absurdly lowfrequency and an absurdly high voltage. The ref designators somehowgot 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 towarn them to be suspicious about cases like this, especially on firstarticles.TGIFJohn

Nov 21, 2009 61 Replies

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John Larkin 16 years ago

We're using an external 12 volt supply and one of these

formatting link

which plugs into the mini-ITX processor board. Switched +12 and +5 come out of it and power our spectrosopy board (which has 5 more switchers and 3 linear regs of its own) and has power distribution for the hard drives. Seems to work.

This instrument is basically a PC, but we don't want it to look like a PC. Most PCs are wiring hairballs inside.

That AC powered fan is temporary. We'll use a temperature-controlled DC fan in the real rackmount box. The Kontron has a connector for that.

John

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JosephKK 16 years ago

Kinda cute. Nice to know such exists.

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