EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: Things on January 05, 2013, 06:47:17 am
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So I was disassembling an active USB extension cable that was throwing a device unrecognised error. Apart fromt he shoddy construction, something else caught my eye ...
(https://dl.dropbox.com/u/203420/DSCF7255.jpg)
Whhhaaaaaaaaaaaaattttt?? ??? ??? :o :o
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Unsolder it and you will find a crystal that is probably not the 12MHz needed................ Or they had a damping problem or needed a spacer, or had a lot of spare resistors that they did not want to just throw away..
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120% of my wat.
Best guess is that it's either factory surplus, or somehow to do with spacing / padding, although as Things mentioned it was inside a poured rubber moulding.
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Don't see how soldering a resistor on top of a metal can is going to change any electrical characteristics. A spacer is an option, but it was enclosed in rubbery plastic potting that had obviously just been poured onto the board, so I don't see the need for it at all.
Excessive resistors at the factory is our only explanation to far :P
I just unsoldered it and can't see the specs because of the solder, but it's definitely just metal can underneath.
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That is one of the most bizarre things I've things in a long time!
Dave.
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The fact they also used a 4 port hub chip in a single extender cable is also kind of amusing. Some engineer was clearly on the good stuff when they designed this ;)
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I have had the GL850 in a few problematic hubs over the years. Second only to the mystery epoxy blob for problems.
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An underpaid, overworked, EXTREMELY bored factory worker with a weird sense of humor?
That's just odd.
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Would be interesting to test if this actually has any effect on the crystal .. anyone with the gear wanna give it a go in spare time? :D
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Probably was the cheapest chip. Most likely the chip was a subgrade part and should have been destroyed but found it's way out of the factory.
the resistor would only degrade the crystal as it would have made it drift again due to the thermal shock.
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An underpaid, overworked, EXTREMELY bored factory worker with a weird sense of humor?
That would be my guess as well.
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Has to be a mechanical spacer - maybe needed for a different version of the product. Bear in mind if the PCB was reflowed with the xtal, it wouldn't have had to be hand soldered - just pasted and placed.
If it was a much higher value I suppose it's possible sometone said "Put this resistor across the crystal..."
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If it was a much higher value I suppose it's possible sometone said "Put this resistor across the crystal..."
Haha, someone wasn't switched on that day :D
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Maybe the crystal and resistor came out of some recycling plant that used a solder bath to dislodge components and somehow it got stuck on top of the crystal?
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I'd guess at either:
- someone wants to deliberately obscure the markings on the crystal, to disguise its type or origin, or
- the factory simply misinterpreted an instruction from the designer, and nobody involved in the manufacturing process has an IQ above that of the average hedgehog.
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I can't remember where an when but I think I've seen a chrystal with a resistor slapped on top before. I just dont know where ... :/
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ooo this is not uncommon in neverland, they forgot to remove the resistor from pick and place plot from previous prototype.
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It's soldered in place, though, so it can't just be a p&p error.
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I want to work at fox-conn and make fun electronics jokes for you people to enjoy.
Why is there an inductor across the data clock??? :scared:
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Could it be a lateral-thinking kind of batch, line or tester number tag? Or maybe a date code?
"Oh, 5R6, that's Mr Wang."
The weird thing is the solder on that resistor looks awfully neat for hand soldering. More like vapor phase reflow, ie done in the same process as the other parts.
Maybe someone has a very odd understanding of the term 'pullup resistor'?
All assuming the OP isn't pulling our legs. Up, or whichever way.
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Many years ago, I took apart a USB extension cable and found the exact same board, also with a resistor on top of the crystal.
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Hah, really?
Glad you brought that up because I knew it wouldn't be long before suspicion set in. Definitely not pulling your legs, even got the plastic molding with resistor value embedded in it for proof :D
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A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency.
Source : http://en.wikipedia.org/wiki/Crystal_oscillator (http://en.wikipedia.org/wiki/Crystal_oscillator)
Now what if you have bad luck, and the metal can housing of the crystal happens to resonate at exacty the same mechanical frequency as the crystal. :palm:
This could effect the electronic functioning of the crystal. You now have to deal with something that normally never is a problem. |O
All the crystals are already bought and in stock, so you better come up with a solution before noon. :scared:
One solution could be to change/lower the mechanical resonating frequency of the metal casing by adding weight to it, for instance by soldering a resistor on top of the casing. :phew:
Back to the more important work activities. :=\
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Good thought but there are many designs using the same 12MHz crystal with no damping on them. I would guess this is a method used to tell who did the manufacture of a specific batch of the units, each being allocated a different resistor value that was available cheap.
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I reckon they just did it for a laugh, simple as that....
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To whoever was trying to design the temperature controlled crystal oven: I don't think you're doing it quite right! :)
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You've got to unsolder it and see what the crystal says.
THE CRYSTAL KNOWS ALL!
PRAISE BE TO THE CRYSTAL!