Possible improvement to PLCC piggybagging in the A600?

protek

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I was wondering, how big a clearance there is between the CPU of the A600 and the keyboard? The contact between the CPU of my A600 and expansions has been somewhat flaky and I've been trying to think a better solution for attaching the expansions.

One solution that should be doable with off the shelf parts would be that the CPU would be desoldered from the mainboard and a PLCC socket would be soldered instead. The CPU would be then placed to the socket. Small pins would be placed in the small crack next to each socket contact. The pins would protrude about 2-3 mm from the socket surface. The socket of the expansion card would then connect to the pins the same way, making a firm connection.

The pins in socket method has been successfully used in Alan Hourihane's IDE board for Atari STE, where the 68k is in PLCC socket. The pins of course are directly soldered into the IDE board but using an extra socket and pins would keep the expansion boards intact.

What do you guys think, would this be feasible?
 

Ed.D

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Hi Protek, not sure I understand. You want to remove the CPU, solder a PLCC socket where the CPU was, then how would the CPU attach to the socket? Is it like the A1200 CPU or are the legs already bent to the PLCC form?
 

roy_bates

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there is enough room there to fit a plcc socket mate:)

you dont need to do anything elaborate mate these sockets come in surface mount flavors.


EDIT: hmm,i might be reading and understanding this the wrong way....


EDIT2: yeah,i suppose its doable looking at the card you mentioned...height under the keyboard might be a problem though...
EDIT3:bare in mind most cards for the amiga uses a inverted plcc socket mounted on the cpu...this will be a real problem reverse engineering as the socket has staggered pins...hope you understand what i mean mate as this is a real problem in regards to straight pin headers alignment wise at the pcb.
 
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protek

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Hi Protek, not sure I understand. You want to remove the CPU, solder a PLCC socket where the CPU was, then how would the CPU attach to the socket? Is it like the A1200 CPU or are the legs already bent to the PLCC form?
The CPU is in the newly installed socket on the motherboard. The pins connect the socket of the CPU and the socket of the expansion board together. There is a small crack between each contact and the casing of the PLCC socket that can accommodate a small diameter pin.

- - - Updated - - -

Here's a rough illustration of the principle:
a600.png
 
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roy_bates

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you might be adding 5mm to the total height this way,its not just the pins and the spaces but the socket also has to be taken into account as that has more height than the cpu.

i also think you would have to use a square profile pin assembly for best contact,aligning this together will be a problem between two sockets.
 
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protek

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The goal would be that the two sockets would be flush against each other, when connected, so measuring from the surface of the A600 motherboard it would be the height of the two sockets plus the thickness of the expansion board and its solderings.
 
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roy_bates

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pins would have to be 1.27mm apart from each other,your talking about placing pins one at a time into a socket it wont be easy aligning all of this bud.
doing this without the spaces for support would be near impossible mate pins would have too much movement in the sockets to be reliable.
you have to be really careful:)
 
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protek

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Good point, Roy. The ST IDE board was a b**ch to insert even though the pins were soldered into the board.

What we really needed was a socket that was specifically designed to connect to a surface mount PLCC chip. A ZIF type one that would fasten securely and make good contact with the chip contacts, when it's tightened.
 
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Ed.D

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If you were to change the upper PLCC socket and make a new plate/block that accepted the pins through holes and then have the pins with feet on them which would solder directly to the upper board, that could work. Solderable pogo pins might work if the correct shape and size could be found.

protek_cpu.jpg

I don't know how good a contact you could make between a pin and the socket on the lower PLCC contact. Would it also interfere with the springiness of the lower PLCC contacts?
 
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Bryce

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Just my two cents: I super-glued a small flatheaded M3 screw to the top of the CPU (inverted: head on CPU with threaded part facing up). This screw then protrudes through the expansion PCB (there's a hole in the centre of the socket) and I then added a nut that holds the PCB firmly in place. See picture, because that's a crap description.

Bryce.

PLCC Expansion fixing.jpg
 
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