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Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

Dang, really don't know what the issue could be. I'll try to add the other two banks to my setup soon and see if I have the same problem.

VERAULT said:
Can this be installed if you already have the 2mb ISA card from Compaq?

Any thoughts on building a psu replacement for the portable II in the future?
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I went back and looked at some old ads, and they did actually market it as having 4.1 megabytes! So that's 640K, plus 1.5M from this board, plus 2M from the ISA board.

The PSU would take quite a bit more effort to actually reverse engineer. A good useful solution would probably be an ATX adapter like the PicoRC.
 
btb said:
The PSU would take quite a bit more effort to actually reverse engineer. A good useful solution would probably be an ATX adapter like the PicoRC.
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Do we have the proper pinout of the cardedge connector the psu connects to. To supply the voltages it needs?
 
Okay, false alarm. Turns out I had some dud 41256's in the AliEx order (shocking I know). Spent the night with a movie and my Retro Chip Tester, but now they're all tested. 3 bad chips in an order of 100 ICs, so not actually too bad, although they're all 100% remarked and definitely not originals...

Anyway she boots and gives the full 2.1MB compliment! Success! Amazing work @btb, this is so amazing :)

20240501_202824.jpg
 
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Amazing work on the board layout, that's quite a good reproduction of the original Compaq board!

Now, is there a 2MB ISA card available that will work, or does the Compaq 2MB card need to be cloned?
 
Yeah, just cosmetically it's amazing @silvervest congrats!
My assumption is that any ISA memory board that can be told to start at the 2.5MB address space will work. If someone wanted to send me a board I could reverse engineer it. However it most likely has a PLD or two on it, and I don't have any experience cloning those.
 
This is amazing! I just got a Compaq Portable II (two of them). I'm very interested in what you guys come up with here. Are these going to be available as gerber files and parts list?
 
Wow, this is awesome! Great work to all involved. I'm a big Compaq fan (obviously) and seeing all of this hard work being invested into the awesome Portable II really warms my heart. Those original memory expansions are extremely rare, so having a reproduction option will be very good!
 
silvervest said:
Yes! The gerbers, an interactive BOM, and all the KiCad source files are available in @btb's repository at https://github.com/btb/PortableIIMemBoard
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I'm going to get the parts and the board made up...I haven't done this before so I have a couple questions on the BOM.

#1 is 47uf capacitors, I assume these are tantalum, but what voltage?
#2 same question, what voltage?

Thanks for the work on this, and thanks for the help!
 
twconstantine said:
#1 is 47uf capacitors, I assume these are tantalum, but what voltage?
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They're actually 47nF and regular ceramics, so voltage doesn't matter a lot. I used 50V - https://au.mouser.com/ProductDetail/594-K473K15X7RF5UH5
twconstantine said:
#2 same question, what voltage?
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These are 10uF 16V tantalums - https://au.mouser.com/ProductDetail/581-TAP106K016CRW

As a note as well, for U57 you don't necessarily need to source a SN74S734 - I used an AM2966 which is a direct replacement, and it may be possible to use a 74S244, but that's untested
 
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