Recent content by btb

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...

As far as I know this is correct:

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. 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...

This looks to me just like the 7250 I have. All discrete logic. The 7270 uses a Z80 or something as I recall.

I've been dismayed once or twice that SS-50 systems don't really fit any of the existing genres. Threads for them usually end up in the S-100 forum I think? Maybe that could be made official in some way?

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!

Just got my experimental board delivered. Hopefully can start testing soon!

I think some of the header pins should also be going to the actual turbo switch, as well as to the motherboard’s turbo input. My guess is that every other row of the selection pins is connected to ground or 5v depending on the type of display used. Half of those are active in turbo, half in...

can't quite see the power connector, but it looks like it is the 6 pins in a line variety, which gives it away as a Unitron-type clone

Oh, I glossed over what you said about them all seeming to die in the same way. interesting

I have a working power supply, although I'm not sure what I can tell you that you can't already see from one of your several supplies, working or not. C13 is a dipped tantalum, marked 156 +25, which I take to mean 15uF, 25V.

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.

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.

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...

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...