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Upgrading CPU and memory on 286 motherboard

sergey

sergey

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Joined
Jul 15, 2010
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Location
Silicon Forest, Oregon, USA
A year ago I upgraded a 286 motherboard that I bought from eBay. I replaced the on-board 1 MiB RAM with 4 x 1 MiB SIMMs, and more importantly upgraded the CPU from 12 MHz to 20 MHz.
It is all not a rocket science. But I documented the process and posted the pictures here for everyone's convenience.

Interestingly enough the board and the CPU will overclock to 25 MHz without any problem... Probably the fastest 286 ever :)
 
Nice, would be interested to see LandMark results at 25MHz - though I guess it should scale pretty linearly.
 
Very accurately timing. I just bought similar board:
http://aukro.cz/show_item.php?item=4001464194
It did not arrive yet

It has no RAM and actually only now I spotted, it has unusual ?? connector for SIMMs ? I have some old SIMMs and wanted to use them there. Now I am really unpleasantly surprised. Can I at least use 644256 RAMs ? I have some of those too.
 
kb2syd said:
Can't you make a SIPP out of a SIMM with some machine pins, solder and a lot of patience? I'm sure I read that somewhere. Can someone please confirm or deny?
Click to expand...

SIPP and SIMMs have exactly the same pinout. So with some effort you can install SIMM modules. There are at least three methods (from easy to more difficult):
1. Get SIMM sockets and plug them in to the SIPP sockets. Plug SIMMs into sockets.
2. Solder pins to SIMM pads, basically make SIPP modules out of them. You can use chopped resistor pins or some ~0.4mm wire for pins.
3. Unsolder SIPP sockets, solder SIMM sockets instead.

Of course you can try to get SIPP modules, or even make your own memory board and solder it. 30-pin SIPPs/SIMMs schematic is really simple. For 1 MiB SIMM it is usually two 4 x 1 Mbit DRAMs + one 1 x 1 Mbit DRAM for parity. Sometimes (on older SIMMs) they used 9 x 1 Mbit DRAMs.

Edit: Here Jameco has dual 30-pin sockets. Really cheap - $0.19 for each, but you need to buy 10 of them... so $1.90 + shipping, not a big deal anyway.
 
Stone said:
If you call soldering 60 pins per SIMM module easy will you let me send you some soldering work of mine? :)
Click to expand...

That's the thing with soldering. Some think it is trivial (I'm one of them) others just never seem to get the knack. I started by soldering pipes while working with my dad (a plumber). Putting an entire water and heating system in a 3 story house used to mean a whole lot of soldering. A lot harder than a 60 pins.

Here is how I would do it:
Solder on one pin (somewhere in the middle)
Put the pin in the SIPP socket for alignment.
Carefully solder in the next 29 using the socket as the place holder. Don't get anything too hot.
Do a pin on the end then one in the middle, alternating to spread the heat.
So, solder a pin on 15. Snap in place. Then solder 1, then 16, then 2, then 17, then 3, then 18...

That way you'll get all of the pins lined up correctly and set at the same height.

Get something like this to hold everything in place as you work:
http://www.ebay.com/itm/Helping-Han...ng-Iron-Rest-2-Articulated-Arms-/330941472191
 
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