25060Re: [midatlanticretro] Re: FD 1771 - Floppy Drive Controller TAX?
- Apr 4, 2012On 04/04/2012 10:12 AM, Bill Sudbrink wrote:
> Ok, here are a couple of weird things that have "bit" meI've seen this failure mode as well. In one case, microscopic
> in the past:
> Cracked pins. I have had TI pins crack in such a way that
> they looked good in place, would test good with a probe but
> were bad during a run. I've seen two kinds of cracks.
> Warning, bad ASCII art follows:
> | | <-1
> | |
> \ /
> \ /
> || <-2
> I have seen cracks at position 1, right where the pin makes
> the bend to go into the chip body. Straight across the bend
> on a soldered chip. Almost invisible to the naked eye.
> Pressure from a probe on top of the pin closed the crack and
> made the pin look good under test.
> I have seen cracks at position 2, at the bottom of the taper
> where the pin narrows to its insertion width. I have seen this
> in both soldered and socketed chips. In the socketed case, I
> stupidly didn't notice the missing piece of pin through several
> removal/insertions. Under test, it can behave just as above,
> with the pressure on the pin closing the circuit.
examination revealed that the only thing holding the pin together was
the thin layer of oxide. That was a serious pain to track down.
Dave McGuire, AK4HZ
New Kensington, PA
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