Evil Dave was prospecting up in the Superstition Mountains and found
some Fool's Gold.

This is a twisted tale, but it bears telling...

A long time ago, in the new magic land, IBM built a system to compete
with the clones. It had to contend with cheaply built clones, so there
was some offset due to better engineering, but holding down the cost of manufacture helped to add to the bottom line.

The 8550 took advantage of automated assembly. I documented a number of ease-of-assembly features in the 8570. These features were used in the 8550.

One feature was the edge connector socket used in the 50 / 70.

https://ardent-tool.com/50_70/Power.html#8570_PSU_Removal_and_Cleaning

This connector had 25 pin-pairs. The connector housing was soldered to a
PCB, and the individual wires from the PSU were soldered to the PCB.

The design had some limited freedom of movement, allowing for
mis-alignment during assembly.

Note the connector housing is thick n beefy. It is built as a
board-mounted socket.

The 8550 had a massive 92W PSU, the 8570 a stupendous 132W PSU. Both
shared the same style of plastic drive shelf, it accepted ONE HD and TWO
floppy attached drives.

Now let's consider the 8590. It used a 486 from the get go [-402 was a
special bid], it had a metal drive shelf in the front, it could take two
or three 3.5" drives, a few floppy connected drives, and it had 8 SIMM
sockets. It came with an XBOX HUUGE 194W PSU.

But, IBM had chosen not to use the [bulky] 25 position connector, but redesigned the power to use two nine position [18 contacts each]
crimp-on terminals. These terminals look to be the very same part used
in the 50 / 70, BUT they were crimp-on. Note that IBM was able to
dispense with the PCB and soldered wires, plus they reduced the contact
count from 50 down to 36.

Here is where things get murky [er]. Note that the 90 has hard solder
deposited on the planar power leads. All the folks that designed this
are retired, or dead, or both...

I tracked down the original terminal housing, and foundt the split-pin terminals. BUT the new versions of the connector housing have a
reinforcing rib about mid-way. MAJ Tom is of the opinion that the
original design in the larger sizes [over 8 pin-pairs, IIRC] was prone
to spreading towards the middle, and the rib was added to prevent this.

Dave has sent a picture of some wire spring clips that were used on a
late production 5494, it appears this was a "fix" for the housing
opening up.

I'm not sure of the use of solder on the Model 90 planar power contacts.
Maybe it was to prevent damage to the gold plating from repeated removal
/ replacement, -OR- it was a "fix" for the widening of the original
housing buy increasing the thickness that the terminals slid over, or both?

--- SoupGate-Win32 v1.05
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