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Any1 with GRiDCASE 1520 or 1530 with floppy/hard drive backplane, take pictures of the backplane?

T

tschak909

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Can somebody with a 1520 or 1530 GRiDCASE take pictures of the floppy/hard drive backplane? I am going to try and make a replacement.
 
I could swear that I had a picture of my backplane but I cannot find it.
I might be able to take some photos this week.
BTW it's a 1520 but it shouldn't matter.
 
Yeah, the 1520s and 1530s used the same core architecture, and many of the internal parts are interchangeable.

The 1530 that was just gifted to me is a model made for the Danish market (I forget the name of the OEM), it has a different VIDROM board in it, which lacks the two application ROM sockets, and instead has an option rom at EC00H that I need to run through Ghidra and see what the hell it is.
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That is quite a nice 1530! Quite an unusual vidRom board. It's most likely because of having to fit the Danish character set they had to design a different board to accommodate (just a guess)?
Unfortunate about the lcd though not the best display unfortunately...
I attached a pic of my standard US 1520 with the rom board from a previous disassembly for anyone curious.
I hopefully will be able to get to pulling it apart today to give you a layout of the backplane.
IMG_0563.JPEG
 
Pics of my dual-floppy backplane, looks like a 244 driver and a 273 octal d-type flip-flop on the board. (why the latter? REALLY need those schematics!)

But the good thing about the pre-Tandy GRiDs? relatively standard components!
20220801_132248.jpg20220801_132211.jpg
 
tschak909 said:
(why the latter? REALLY need those schematics!)
Click to expand...

You should be able to trace that out with a VM probe, and definitely document it. I'm going to hazard a guess that maybe for some reason the drive select/motor on signals from the motherboard are provided as strobed signals? (IE, it sends toggled on/off states for those instead of latching them on board.)
 
Plot thickens. Now I understand WHY the vidROM board doesn't have any application ROM SOCKETS:
20220801_193457.jpg

It's a VGA card. Cirrus Logic CL-610 series, which, based on the configuration I see here, 640x480x16 colors, as well as MCGA support. Very unexpected!

-Thom
 
Ugh. Multilayer circuit board so it’s impossible to work out the schematic from just a picture, and it has a GAL (programmable logic) on it. I wonder what in the world that is doing.
 
I don't know what it is doing either...
Maybe something vendor specific (Epson floppy drive controller perhaps?)?
 
The floppy only board had the ‘273 latch and a ‘244 buffer on it, which are also on this board. The new parts are a pair of ‘245s and the GAL. What’s interesting about that is you could pretty much build an entire ISA IDE port with those pieces; the ‘245s are the bidirectional data bus buffers and all the address decoding would easily fit in a 20v8. (I know, I’ve fit an XT-CF in one with plenty left over.) Is one of those ribbon cables just a nearly complete ISA bus?
 
The ribbon cables seem to be standard PATA(? IDE) (although I haven't tested any of the pin outs and I am a bit rusty on these), but it is surprising that it has those pieces for ISA bus.
Perhaps there is an adapter that would allow ISA?
(I know PATA is an ISA subset, but it doesn't seem to be utilizing its full capacity)
 
Again, the fact that most of the signal traces are hidden doesn’t make this easy, but you can see that the ‘245s are on the IDE data bus pins. If the cable coming to this board were already fully qualified PATA I’m not sure why they would push the buffers to the wrong end of the cable.

Did they make a version of this that took an MFM drive? If there was a daughterboard that had the MFM controller chip on it this design would make sense.
 
I reversed this board a year or two ago and made my own that plugs in to my GRiDCase 1520 and performs the same functions as the original backplane but also gives an ISA slot. It was a proof of concepts so the computer couldn't be reassembled with an ISA card sticking up vertical but I've been working on a new revision that solves that and consolidates all of the logic (and the GAL) into a single CPLD. The GAL is just doing IDE decoding and backplane gridbits ID. I ran a sound card and a VGA card. I had some trouble getting soundcards working, ended up only getting two going... some weird garbage card and a Vibra 16.
 
I found some more notes and schematics I drew up. I realize I've forgotten much of this stuff but I'm pretty good about keeping records... so I'll try to make it all accessible. For now though...
  • The 244 and 273 are for backplane identification.
  • If it has a GAL it's for decoding (such as for IDE)
  • If it has a pair of 245's they are buffers/latches for IDE data.
 
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