[rescue] Slightly OT: Bad Cap Saga
Geoffrey S. Mendelson
gsm at mendelson.com
Tue Aug 19 12:29:20 CDT 2008
On Tue, Aug 19, 2008 at 10:02:17AM -0700, Curious George wrote:
>No, different issue entirely. The device didn't exist -- we
>wanted them to make one for us. Since we were unfamiliar with the
>tradeoffs involved in *that* design process, we couldn't on our
>own come up with specs that would have ensured an economical design.
Ok, now that really confuses me. Following your example below:
(to avoid more confusion, I'll wait for others to read it)
>By way of an arbitrary (and fictional!) example: imagine you're
>asking them to design a thermal printhead assembly. This is
>little more than a bunch of resistors with digital switches
>controlling each individually.
>>From the physical (thermal?) standpoint, all you care about is
>the dimensions of the element and getting a certain amount of heat
>out of it in a certain time interval.
>So, a zero-th order approach says "pick an R and specify V to get
>the desired amount of power dissipation".
>But, as V goes up, there are consequences to the switching devices
>(i.e., must have higher breakdown voltages). As V goes down (because
>R has been picked as a lower value), there are *other* consequences
>for the same electronics (e.g., I goes up).
>What's *their* (manufacturer) process technology like? What's the
>sweet spot for the control electronics?
>What ramifications does this have to the geometry of the resistive
>devices? Does it affect the technology used to deposit them on
>the "printing surface"? Does it affect reliability? Does it
>affect the cycle time of the elements (thermally)? etc.
>The cost of learning this is far outweighed by the "cost" of
>outsourcing the problem completely. So, what you're wanting is
>to engage in an *engineering* "give-and-take" (i.e., a dynamic
>design process) with the supplier to figure out how to find that
>sweet spot. Obviously, the changes made in the printhead's
>design will have ramifications to the rest of the system -- things
>that the supplier will not be aware of (hence, he's in the same
>boat as you -- except the mirror image problem!).
Ok, I'm confused. Since it is a device that exists, unless you are
building a satellite for a US company, you just buy a COTS
(commerical off the shelf) unit. I'm not sure about SurreySat,
but most of the small "bus" manufacturers (people who make
cheap satellites) do exactly that.
No, I don't build them I got this info from someone who does and
he tells me about the public information one can find on the web.
>I found that American firms are much easier to get into this
>"give-and-take" sort of specification process. The Japanese
>seem to want to "do what you want" (and just adjust their
Exactly. They adjust the specs to fit yours, but I will bet they don't
adjust the product. :-)
>The cost of replacing/repairing a "bad board" (hence, a
>"defective product") can easily outweigh the value of the
>I recall one medical device designed many years ago where the
>cost of the device (DM+DL) was less than half the cost of
>sending someone "down the road" (locally) to repair it!
>For those devices that you can't just place in a cardboard
>box and *mail* complete replacements, you *really* don't want
>to have to put someone on a plane, etc. to troubleshoot and
>(and that's assuming your customer is content with the day
>or three that this will take)
Then you don't buy the cheap stuff, you buy the expensive, individually
spec'ed and test components. For example, if you spec the board to
work with a "5 nines" 99.999% up time rate at 45c, each component
is spec'ed at 45c or greater and the board is tested at that temp.
Cheaper boards are tested at that temp, no matter what the specs,
and really cheap boards are built with whatever they can get and
"statisticaly" tested, i.e. if they test one in 1,000 and 10 in a row
don't fail, they are 99.999% ok at that temp. :-)
>This suggests the failure rate is driven solely by the quality
>of the components? (or, that the production quality of all of
>these houses are virtually identical)?
Yes, and yes. They use similar materials, similar processes, and buy the
same components. They also do similar testing.
>I take it you are on the rim?
Are you kidding? After all of the posts, I've made on this, you haven't
read my sig once. I'm going to be mean and make you read it this time. :-)
>Yeah -- except they all SNAP together with those frigging
>flimsy snaps!! :-/
Well, that's spec'ed by Dell. Or more likley the consulting firm they
hired to do time study of their processes and recommend how to minimize
>Exactly. When your (my) reputation stands to win/lose based on the
>quality of the product, you want some reassurances that your
>suppliers are as committed to making (not FAKING) a good product
>as you are. :<
Yes. But it also means that you need to test their product. As President
Reagan said about privatising government functions, "trust, but verify".
>No, but, IME, the Industry (pick an industry!) is always much
>smaller than you can imagine. I.e. "word gets around" by
>whatever means. People change jobs and bring their horror
>stories with them, etc.
Sure, but to be blunt, rarely does the customer listen to them.
Geoffrey S. Mendelson, Jerusalem, Israel gsm at mendelson.com N3OWJ/4X1GM
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