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

Made a mini version to experiment with.

Made it to fit in 100mm square, so it's just bank 2, but there's a header to attach 3 & 4. Maybe I'll get lucky and find a way to make higher-density chips work and that ends up unnecessary?

Also, has the components on the opposite side and mounts closer to the motherboard.

CP2SIMMBoard1Bank.png
 
That's awesome. I'm staring down the barrel of around AU$100 for the fab on the full size boards - x5 but still $20 a pop... A smaller one would definitely be nice!
 
To use 1 meg SIMMs you'd have to OR the three RAS signals into one RAS signal and do some logic to translate those RAS signals into the extra address lines you'd need, if I'm thinking right. Since write enable is tied together for all three banks at the motherboard, no need to do logic there.
 
Yeah, even a six-SIMM version, which still takes about half the width of the original would be somewhat expensive. I might finish that version eventually but I think I'm better off doing something super cheap as a proof of concept first.

I may end up trying that with the RAS signals, but first I want to see if these mysterious lines already present on pin B3 and B4 might be just what's needed.
 
I think you can get the extra address lines by ORing (RAS2 or RAS4) for one, (RAS3 or RAS4) for the other. But I'm not sure if there is a timing issue...
 
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So since the AMP 5-102871-1 is EOL and impossible to get, I decided to look for alternative headers. The Samtec TSW-126-17-T-D fits the dimensions nicely, but is a bit breeze-flappy, and since I wanted to recreate this as close to original as possible... well, I did that!

Have now modeled the AMP 5-102871-1 and left a bit of a gap for the TSW-126-17-T-D to fit in nicely. Will share STLs shortly, but here's what the two parts together look like, and just the housing shell alone which is what I will be resin printing to suit. Not sure where to get rivets from but that might end up just being optional :)
 

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nice. Yeah, i think they're just screw holes into the plastic, that went unused.

That sounds like a pretty much ideal solution, silvervest, I like it! It's not even that far off from how the original is constructed, as far as I can tell.
 
oh of course, I just meant how the original appears to be made up of two pieces, a base that the contacts are integrated into, and a shell that goes over that.
 
IMG_8495.jpegIMG_8497.jpeg


Holy cow it works!

Those are 1MB SIMMs, but for now it only sees 256K of each one. Not sure what's going on with the parity thing during setup. It passes the memory test in Compaq Diagnostics v8.0.

Have to make some more tweaks before it's really good enough to release, but woow!
 
Finally got some time to dive in over this weekend and got my full board together. It looks amazing and *mostly* works, but it can only see 512K, same as your mini board. Doesn't matter what I put into banks 3/4, it never sees them. Screenshot from FASTART below is with the full compliment of 41256's installed.

I've checked the mainboard jumpers and they're configured correctly as well, so I'm not entirely sure! We must have missed... something...
 

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