Arno wrote:
In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn
wrote:
In sci.electronics.repair Arno wrote:
In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn
wrote:
In sci.electronics.repair Arno wrote:
[...]
Those 4 were fine on the top of PCB. Black stuff was underneath,
on those pads contacting with springy heads pins.

Mine is fine on both sides. However there is a quite a bit of
contact area that looks and feels silver-plated to me, most
notably areound the screws and on the bottom the contacts to the
head assembly.

That makes me wonder why are they silver-plated. It is definitely
not the best material longevitywise, especially for such low-level
signals. It makes me even more suspicious and adds to the
conspiracy theory.

Well, maybe. However I tend to think that "never attribute to
malice what can be adequately explained by stupidity" may apply.

I agree but it looks like there is a pattern here...

These contacts should be gold plated with high quality gold. It is
also possible that the HDD vibration (always present with a running
HDD) and thermal variation allows the process to creep between the
contacts and kill them. Maybe a young, inexperienced engineer was
hired to replace an older, experienced (but more expensive one)
and that person made a pretty bad judgement call due to
inexperience, wanting to save a few cents on the design.

They did not save anything on that design. Gold plating is a common
procedure, it is everywhere, most of card-edge connectors (e.g. PCI)
are gold and they even called "gold fingers" by chinese PCB
manufacturers.

Silver, on the other hand, is almost unheard of and I'm pretty sure
PCB makers would charge extra for this if they agree to do it at
all. And it is NOT that the entire board is silver-plated; there are
gold-plated parts on that same board that makes it have at least 2
different platings so it will be more expensive than simple gold all
over.

Good points. An exotic process would be more expensive than a
common one and two processes instead of one as well. I also happen
to know that putting gold directly on silcer is problematic, but
putting it directly on copper is fine. At least that is for galvanics
on jewelery and if I remember this correctly.

I have to say that the last time I saw silver plating as contact
protection was in vaccuum tube equipment. Modern electronics
typically uses Gold, or Tin for low insertion cycle contacts.

Yep. Silver plating was usually used in microwave equipment, HF
coils etc. where skin effect was so profound that current only ran
through that silver (that was quite thick, btw.) Silver is also used
for HIGH CURRENT relay contacts where the corrosion is removed by
mechanical action of closing contacts and burned through with high
current.

That explains it. I have indeed seen it in power relais as well.

If you look at low current signal relays with stated minimal current
capacity _NONE_ of them have silver contacts. It is usually gold,
platinum, rhodium, or a mix thereof.

I am all pro Occam's Razor but all this looks like deliberate effort
to make it fail after some time. It is NOT easier or cheaper to
put silver there because it is an _ADDITIONAL_ step and not so
common one.

Well, it only makes the required level of stupidity larger,
because (if we have this right) they also need to mess up the
economic angle. If we assume they are competent, then indeed this
looks very much like a deliberate and rather bad design error.

Or some fool has focussed on the price of gold metal and has
lost sight of the fact that more complex pcb manufacturing
process negates any advantage by using the cheaper metal.

MUCH more likely than any conspiracy to shaft the user.