Help with a busted MSV11-L?
Ian S. King
isking at uw.edu
Sun Dec 7 23:41:48 CST 2014
When I was at Living Computer Museum, we were using a small pin that had a
socket (hole) in it. Solder N of those into the board after removing an
IC, and you'd never have to desolder another one - an important benefit
considering that some of these boards are losing integrity in the bonding
of copper to epoxy (or never had such integrity, e.g., Data General).
They're low profile (maybe a fraction of a millimeter higher than a
directly soldered-in chip), which can be crucial in some of the crowded
backplanes we see. ISTR that Mouser sells them. -- Ian
On Sun, Dec 7, 2014 at 11:44 AM, tony duell <ard at p850ug1.demon.co.uk> wrote:
> > And should I always install the replacements in sockets, or is it OK to
> > go ahead and solder them straight in? (The socket obviously doesn't cost
> > much, and I'm less likely to damage the chip installing it like that,
> and of
> > course if I get it in and it's U/S, it's easy to swap out from a socket,
> > I'm wondering if the use of a socket has any downside, electrically.)
> Sockets have basically 5 problems :
> 1) Extra stray capacitance between the IC pins. This is the normal reason
> for not using a socket in high-
> speed circuitry.
> 2) Extra inductance of the connection to each pin. This can affect certain
> ICs which need external decoupling
> (e..g for a clock multiplier PLL) as close to the pin as possible
> 3) Extra thermal resistance. This is a reason for not putting some power
> devices in sockets
> 4) Extra height above the board. In your case Q-bus is tightly spaced
> anyway, so check there is enough
> space for the socket you are using.
> 5) Reduced reliability. My experience is that formed-pin (cheap) sockets
> are a pain. Turned pin (machined
> pin, whatever) are fine. I have never had a bad contact on the latter.
> Yes, if you are doing military or medical
> work it will matter but for classic computer systems I don't think that a
> turned pin socket will degrade
> reliability at all.
> Personally, if there are no problems due to the above I solder common TTL
> parts and the like in directly.
> I socket anything expensive, anything hard to find, or anything
> complicated. And of course a programmed
> device (ROM, PAL, etc) gets socketed if at all possible.
> In yuo case I'd socket the Q-bus buffer chip, but not the TTL latches.
Ian S. King, MSIS, MSCS
The Information School
University of Washington
An optimist sees a glass half full. A pessimist sees it half empty. An
engineer sees it twice as large as it needs to be.
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