17 Oct
2012
17 Oct
'12
9:18 a.m.
On Wed, 17 Oct 2012, David Riley wrote:
On Oct 17, 2012, at 10:10 AM, Liam Proven wrote:
> On 17 October 2012 13:05, David Riley <fraveydank at gmail.com> wrote:
>
>> To my recollection, the 386SX only came in surface- mount packages.
>> The N8VEM folks (including the S-100 group) have done a pretty good
>> job of making sure all their boards can be assembled with only
>> through-hole parts, which makes it a lot easier for novice solderers
>> with cheap irons.
Despite how they look, QFPs are among some of the easiest surface mount
parts to fit. A 25W pencil iron with a small tip (~2mm) and some liquid
RMA flux will do the job. I've used irons with tips as large as 4mm for
this task when in a bind. Granted, I've been soldering for decades, but
still...SMT isn't /that/ hard...
IIRC, the i386DX is currently still available from Intel in a QFP package
and is marketed for embedded applications.
> Yes, they were Quad Flat Package things, but QFPs
came in a socketed
> form sometimes - I fitted a few of them myself, even though I was/am
> primarily a software guy.
It was also extremely common to see AMD 386DX QFP chips fitted onto a PGA
carrier board that could be plugged into a standard i386DX socket. I own a
bunch of these (and motherboards for them) which I plan to use for a
future multi-processor project. [That is, IF I can ever get my hands on
enough 40MHz 387DX math co-processors -- one guy on eBay has had them for
more than 10 years but his per unit price makes my project cost
prohibitive since I need at least a dozen of them.]
Is it possible that there was an upgrade PGA socket
present on 386SX
motherboards alongside the surface-mounted chip? I sure see quite a few
examples of what looks like that (possibly a socket for a 387SX
instead).
Such boards were very uncommon but they did exist. Just as there were some
"universal" motherboards with PGA sockets for both an i386DX /and/ an
i486DX, there were some motherboards with an on-board i386SX plus a PGA
socket for a i386DX (and a second PGA socket for an i387DX). There were
even boards with 4 PGA sockets, i386DX, i387DX, i486DX/SX, i487SX (I own
some examples of these boards). These "universal" motherboards were not
very common and were typically about 1-1/2x to 2x or more the price of a
normal motherboard. Many people who had these boards installed in their
white-box clone PCs never even took advantage of the extra upgradability
options.
The standard socket for an i387SX was a PLCC socket.