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From: Joerg on 20 Nov 2009 20:32 Joel Koltner wrote: > "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message > news:u0beg512h0fcels3arn2i6s9f8vcc6cqa9(a)4ax.com... >> The resistor that's screened "R127" is actually R129. And vice versa. > > I (cough!) think most of us have had that happen... > Mine were usually followed by ... phut ... *PHOOMP* > What's the big yellow silkscreened square around the oscillator-in-a-can for? > Metal shield maybe? > It's probably the no-step area, per ISO-9000 :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Phil Hobbs on 20 Nov 2009 19:27 John Larkin wrote: > 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 > > > Better complain to the head of Engineering. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: John Larkin on 20 Nov 2009 21:05 On Fri, 20 Nov 2009 19:57:43 -0500, "Martin Riddle" <martin_rid(a)verizon.net> wrote: > > >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >message news:u0beg512h0fcels3arn2i6s9f8vcc6cqa9(a)4ax.com... >> 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 >> >> >> > >Yea, know the feeling. >Most people I've talked to agree that the first board always has some >sort of problem(s). > >Cheers > 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
From: Joerg on 20 Nov 2009 21:21 John Larkin wrote: > On Fri, 20 Nov 2009 19:57:43 -0500, "Martin Riddle" > <martin_rid(a)verizon.net> wrote: > >> >> "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >> message news:u0beg512h0fcels3arn2i6s9f8vcc6cqa9(a)4ax.com... >>> 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 >>> >>> >>> >> Yea, know the feeling. >> Most people I've talked to agree that the first board always has some >> sort of problem(s). >> >> Cheers >> > > 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. > 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 http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: a7yvm109gf5d1 on 20 Nov 2009 21:24
On Nov 20, 7:22 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > 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 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. |