Help with a busted MSV11-L?

tony duell ard at
Sun Dec 7 13:44:41 CST 2014

> And should I always install the replacements in sockets, or is it OK to just
> 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, but
> 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.


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