Sun SPARCstation LX boot from CDROM?

[Tom Hunter]

Hi Liam,

You are probably quite correct.

In another forum someone came up with the same explanation for my "rat
problem".

Here is what he wrote:

"Were there any electrolytic capacitors in the region of the corrosion?
When an electrolytic capacitor leaks (even slightly) the electrolyte often
contaminates the solder joint and oxidises it as you describe. The
appearance will be dull and the melting point will be significantly higher
than that of normal tin-lead joints. When heated, it will emit a "unique"
smell that smells like fish or urine. This is often repairable but it's
quite a bit of effort. Worthwhile for high-value assemblies I suppose."

and:

"With regards to small electrolytic capacitor leakage, I very rarely see
any "wetness". The leakage takes place very slowly over many years and is
almost like a capillary effect along the pads and into the board rather
than a liquid spill. One normally only sees the damage (oxidation). It
usually discolours the pads of the electrolytic cap and then travels into
other nearby pads too. It often eats up the solder mask very quickly, but
it takes longer for it to eat up the copper tracks. If your board is
multi-layered, that is a very unfortunate situation indeed! Attached is a
photo of what capacitor leakage typically looks like (note in this photo
the offending caps have been removed and their pads cleaned)."

I cannot include the photo as this mailing list doesn't allow photos.

I think both you and the guy I quoted are spot on and this explanation is
much more rational.
I was misled by the smell when trying to reflow some of the pads.

So the "rat mystery" is resolved. All I need now is a replacement drive.
:-)

Thanks
Tom Hunter

On Tue, Sep 1, 2020 at 8:15 PM Liam Proven via cctalk <cctalk at classiccmp.org>
wrote:

> On Sun, 30 Aug 2020 at 15:33, Tom Hunter via cctalk
> <cctalk at classiccmp.org> wrote:
> > About 70% of the PCB had solder joints that were nice and shiny like
> brand
> > new. The remaining section near the front of the drive was quite badly
> > corroded and it also looked like there was some liquid spilled over that
> > section of the PCB (component side).
>
> This and the rest of what you describe sounds quite like the damaged
> caused by electrolyte leaking from failed capacitors. This is probably
> the most common cause of failure in electronics after they get to 2-3
> decades old.
>
> There was one particular time when this happened prematurely:
> https://en.wikipedia.org/wiki/Capacitor_plague
>
> But it is a general problem with almost all capacitors.
>
> I could be wrong but this seems more likely than rodent pee...
>
> Personally, I have failed caps in 3 Apple Macs -- one PowerPC and two
> MC68000. All are awaiting repair.
>
> --
> Liam Proven – Profile: https://about.me/liamproven
> Email: lproven at cix.co.uk – gMail/gTalk/gHangouts: lproven at gmail.com
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>