Author Topic: Cystal can corrison  (Read 3638 times)

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Offline rgammans

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Cystal can corrison
« on: September 30, 2015, 08:13:44 am »
My other halves radio alarm clock has broken, so it the interests of harmony I offered to see if II could fix it. It is an expensive one, which lights up slowly. (lumie bodyclock) .

It seems to have a uprocessor and all sorts inside. Most of the function seem obvious by board placement with a few oddities ( Like the mmc port).

What I noticed was near a coin cell type battery ( rtc backup I guess) - which itself doesnt appear to be effected, there was a xtal can ( cylinder type) with a lot if corrosion around the legs and that end if the can.

I've never seen corrosion start around a cystal before, has anybody else ?

If peeps are interested I might post some pictures tomorrow when there is more light.
 

Online PA0PBZ

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Re: Cystal can corrison
« Reply #1 on: September 30, 2015, 08:42:00 pm »
Is there maybe a leaking cap close to the crystal? It seems strange indeed that it starts corroding by itself.
How old is the device? And yes, pictures would make discussing it a lot easier.
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Offline Smith

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Re: Cystal can corrison
« Reply #2 on: October 01, 2015, 04:52:46 am »
I just happened to repair an original Gameboy today. It was working, but I opened it up because the LCD had troubles with missing lines (common issue, easy to solve) On the main PCB was a pile of rust. When I removed some of the rust, I found an crystal under there. Took some heavy cleaning, but its clean again. I have never ever seen something like it before.

I have seen a lot of components with the other kinds of corosion.
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Offline rgammans

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Re: Cystal can corrison
« Reply #3 on: October 02, 2015, 05:57:01 am »
 had another look in better light and I think it is just a absolute mass of flux residue.

I've attached a photo, but it isn't clear from the photo - as it was when I lifted the can to confirm check that it's marking matched my guess as to it's frequency (Marked a 32768, which as indeed my guess ;-).

I think I still change it anyway and clean up around there. Perhaps there could be some other PCB damage hiding under that mess.
 

Offline DmitryL

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Re: Cystal can corrison
« Reply #4 on: October 02, 2015, 05:58:52 am »
looks like a glue to me.
 

Offline rgammans

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Re: Cystal can corrison
« Reply #5 on: October 02, 2015, 06:32:34 am »
Maybe, but I'd expect it to actually bond something if it was glue.  There no mechanical adhesion when I move the crystal can.

Whatever it was  - it's now junk - not corrosion.
 

Online PA0PBZ

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Re: Cystal can corrison
« Reply #6 on: October 02, 2015, 06:37:25 am »
looks like a glue to me.

That would be my guess also, you don't want the crystal "flapping in the breeze". Maybe it lost the adhesive powers after the years.
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Online Kleinstein

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Re: Cystal can corrison
« Reply #7 on: October 03, 2015, 01:53:12 am »
Looks like glue to me. I had a similar looking type of glue in an amplifier - over time it seemed to have started getting slighly conductive (possibly corrosion under the glue)  and messed up the circuit. So there is a minimal chance that the glue is a problem, though it's not that likely.

So likely the trouble is somewhere else.
 

Offline mikerj

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Re: Cystal can corrison
« Reply #8 on: October 03, 2015, 02:02:36 am »
My other halves radio alarm clock has broken,

As others have said that is glue which is used to secure the crystal to the PCB.  A more detailed description of the fault would help, do the symptoms point to a fault with the crystal (e.g. clock running fast/slow etc.)?
 

Offline SoundTech-LG

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Re: Cystal can corrison
« Reply #9 on: October 03, 2015, 04:14:53 am »
Definitely glue. Mitsubishi consumer VCRs were full of that stuff mid 80's. It does change, harden, and CORRODE traces and other metals. Get rid of it. On a Xtal it would be particularly troublesome, with unintended leakage, and conduction. Bad idea to begin with. Silicone is the answer for that. Not glue!
 

Offline wagon

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Re: Cystal can corrison
« Reply #10 on: October 10, 2015, 05:31:22 pm »
That brown glue starts off as a white-yellow glue.  Goes brown as it ages.  I think it's hygroscopic, and that moisture is what chews the copper away.
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Offline SeanB

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Re: Cystal can corrison
« Reply #11 on: October 10, 2015, 08:09:52 pm »
Get a new 32kHz watch crystal, and put it in there in place of that one, as likely the one leg has been rotted away under the glue.  You do not really need to use anything to hold the crystal, just a slightly longer lead on it and a drop of superglue on the top of the can to hold it to the board in a clean spot while keeping the can from shorting out anything else on the board. Nice convenient spot is already there between the crystal and the battery, where the soldermask is missing.  Just be careful bending the leads, they are very fragile, I use some tweezers as a support between the can and the bend so you do not fracture the seal. Bend them, and it should drop right in, and then a drop of superglue by the battery side.
 

Offline wagon

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Re: Cystal can corrison
« Reply #12 on: October 10, 2015, 08:59:56 pm »
Neutral-cure silicon is pretty good for sticking down those little crystals, too.
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Offline SeanB

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Re: Cystal can corrison
« Reply #13 on: October 10, 2015, 10:02:28 pm »
Neutral-cure silicon is pretty good for sticking down those little crystals, too.

True, but it is harder to find than the regular acetoxy cure types. You need one marked as safe for use on copper surfaces, and for a single small drop of superglue is both cheaper ( dollar store one is fine in the tiny tube, and you still have 4 unopened tubes left for use afterwards) and easier, just a tiny drop after mounting to hold it down, to keep it from vibrating and breaking legs. It should alreadty be contacting, the glue just providing further hold.
 

Offline wagon

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Re: Cystal can corrison
« Reply #14 on: October 10, 2015, 10:08:03 pm »
Neutral-cure silicon is pretty good for sticking down those little crystals, too.

True, but it is harder to find than the regular acetoxy cure types. You need one marked as safe for use on copper surfaces, and for a single small drop of superglue is both cheaper ( dollar store one is fine in the tiny tube, and you still have 4 unopened tubes left for use afterwards) and easier, just a tiny drop after mounting to hold it down, to keep it from vibrating and breaking legs. It should alreadty be contacting, the glue just providing further hold.
I use heaps of it, I buy it by the cartridge at the hardware shop.  Probably overkill in this case, since he's unlikely to use the other 99.9% of the cartridge before it goes bad.  You can tell it's neutral cure by sniffing it - if it smells like vinegar it's the wrong one. 
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