7 Dec
2014
7 Dec
'14
11:44 a.m.
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.
-tony