Macintosh LC III - FPU

Zensor

New Tinkerer
Mar 19, 2022
14
0
1
hello and a short question: ...how do i install an FPU ? (i do not see any (direction-)markings on the socket.....and stupidly, the FPU is square and fits in all directions) :unsure:

THX :coffee:
 

Nixontheknight

Tinkerer
Nov 3, 2021
124
19
18
hello and a short question: ...how do i install an FPU ? (i do not see any (direction-)markings on the socket) :unsure:

THX :coffee:
There’s an edge in the fpu that looks like it’s two edges, that part of the socket will have two edges as well indicating pin 1
 

max1zzz

Moderator
Staff member
Sep 23, 2021
233
564
93
27
There should also be a dot on the logicboard on one side of the FPU slot to denote pin 1 of the slot, this corresponds with a dot engraved on one side of the FPU denoting pin 1 of the chip

Even though it looks like it should be possible you shouldn't actually be able to insert the FPU in the wrong directionas one corner has a angled edge which acts as a key with the socket
 

lilliputian

Tinkerer
Mar 6, 2022
231
96
28
Los Angeles, California, USA
Like so!

20220404_120238.jpg

As you can see, there is a notch in the corner of the PLCC socket, as well as on the chip, which should be aligned for insertion.
 
Last edited:

Zensor

New Tinkerer
Mar 19, 2022
14
0
1
There should also be a dot on the logicboard on one side of the FPU slot to denote pin 1 of the slot, this corresponds with a dot engraved on one side of the FPU denoting pin 1 of the chip

Even though it looks like it should be possible you shouldn't actually be able to insert the FPU in the wrong directionas one corner has a angled edge which acts as a key with the socket
THX :love:

and.....exact: I didn't see the 2 dots (I also have these dots on the logicboard and they are actually clearly visible - I think I'm getting old) o_O
 

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  • LC III FPU.jpg
    LC III FPU.jpg
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AlanG

New Tinkerer
Feb 24, 2023
1
0
1
Thank you, lilliputian and Zensor for posting those pictures and sharing that information. I recently picked up a Mac LC III to service and restore. I had picked up a FPU and I was scratching my head and sweating the details about trying to figure out how to correctly install it.

Cheers,
Alan G