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Odd duck 386

J

jh1523

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Jan 15, 2009
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coastal New England
Just received a lot of 386 motherboards off ebay - very cheap because it's a mystery lot, no names or specs. One of them I could identify easily, but the other defies me. Perhaps someone here could help me identify it.

Here is the picture, saved from ebay:

ev3000a.jpg


It has the following markings:
(front) AT Plus Inc. EV-3000A
(back) PWB-00230-00 REV.E

Has a 386DX-16 socketed, no 387 socket. Chipset is C&T. memory is 4 banks of DIL sockets, all populated with 256k chips, so 1M total. There are 4 BIOS chips, labeled "rev F1-30", U70-U73. Appears to have been at least partially hand assembled as several components (mainly capacitors) seem to have been manually soldered, also there are several resistors hand-soldered on the back as well as several wire bridges. There's a handwritten note glued on it that reads "386 DX-16, 1 meg ram, 128k cache"

Closest matches I could find are these:
http://bk0010.narod.ru/hardware_specs/m/E-H/31584.htm (same disposition of slots, model number close - it's also called the 3000B)
http://bk0010.narod.ru/hardware_specs/m/E-H/31510.htm (same disposition of memory banks and jumpers - except for the serial/parallel ports which are missing)
http://bk0010.narod.ru/hardware_specs/m/E-H/31581.htm (socketed memory, model number close)

That's as far as I could get. If anyone has further info, it would be much appreciated.
 
PWB is usually a designation I find on Packard Bell boards and cards such as this;

Packard Bell 286X PWB-2149 REL.02
(FORCE 1/AXCEL 1+/PB286N/LEGEND IV/PACK-MATE III)

It could be an Everex Systems board as well. I think PB made boards for a number of other computer companies.
 
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I've visually scanned all the P-B 386 motherboards, none is anywhere close. I think it's an Everex board, but can't find an exact match.
 
AT Plus is usually a Micron board. I've got one here that's even stranger--no memory on the planar.

They also rebadged Everex boards, but I see someone's already noted that.
 
Chuck(G) said:
AT Plus is usually a Micron board. I've got one here that's even stranger--no memory on the planar.

They also rebadged Everex boards.
Click to expand...

Huh, first time I hear of Micron as "at plus"

Ok, off to scan those too...

(edit) Um, I don't think Micron made 386s. They started making computers in 1994-95, past the 386's time. Before that they only made memory.
 
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You know, it looks awfully close to a Mylex MB386. The funny thing is that the MB386 was my first 386 system. I have the manuals (fairly detailed for it). I'll see if I can find them and try to match photos.
 
You say there is no socket for a math-co but I'd bet $20 that the open socket next to the first 16 bit isa slot is for a co-pro. A 287 one.
 
Old Thrashbarg said:
Does this look familiar? Same 3000A model number, same specs... no picture, but it's as sure a bet as you're gonna get.
Click to expand...

Yep, very close. Only the cache appears different (128k on this board). $5000? I'm rich! :D
(edit) the 3000A also appears on the Windows 3.0 hardware compatibility list: http://support.microsoft.com/kb/62098

luckybob said:
You say there is no socket for a math-co but I'd bet $20 that the open socket next to the first 16 bit isa slot is for a co-pro. A 287 one.
Click to expand...

And I bet you're right. I didn't think about it looking for a square 387 socket. :) I wonder if an 8MHz 287 would run there. I know they were operated asynchronously but can't remember what sort of frequency ratio was used.

Chuck(G) said:
Yup, that was very common on early 80386 boards.

Found my Mylex manual--an MI386 board. Not in th99 either.
Click to expand...

According to this http://books.google.com/books?id=nD...Q6AEwAA#v=onepage&q=mi386 motherboard&f=false I don't think what I have is close to the MI386. It apparently came with 2MB RAM- expandable to 8-16MB, the number of ISA slots is different and had a 387 socket.

Thinking more of this board, it looks more and more like someone's attempt to put a 386 on a board made for 286... and those hand-placed components kinda say "prototype". I think this could be the first Everex 386 motherboard model. The hard limit of 1MB RAM kinda defeats the purpose of having a 386 CPU, turning it more into a glorified 8086. And in that case why use a 386DX? A 386SX would have sufficed plenty, and much cheaper at the time (oops, not true after checking facts: the SX wasn't available until 1988, and this board is probably early 1986).
 
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I wonder if an 8MHz 287 would run there. I know they were operated asynchronously but can't remember what sort of frequency ratio was used.
Click to expand...

The ratio wasn't really set in stone, it depended on the board.

I believe I see an oscillator near the 287 socket, right next to the power connectors, and two more near the cache chips. I'd expect one of 'em is probably 14.318mhz, but of the other two, one should be for the CPU clock (probably 32mhz, maybe 16, but they were usually 2:1 with the actual CPU speed), and one should be for the FPU (again, probably 2:1 with the actual FPU speed).
 
This Everex 286 board looks very similar in layout to mine: http://bk0010.narod.ru/hardware_specs/m/E-H/31569.htm

On the 3000A, there are 3 oscillators: one for 16MHz and one for 32MHz, both located near the CPU (there's also a 14.318MHz crystal - not an oscillator but plain crystal, located near these 2), and one for 25MHz located near the FPU socket. There is also a jumper labeled "J5" with no other info crammed between the FPU socket and the nearest ISA slot. I can't trace any connections to the jumper, they must be in one of the inner layers. Can any of this help me deduce what speed FPU I would need?

(edit) after reading the above post (posted almost simultaneously) that would mean the FPU clock rate would be 12.5MHz - correct?

OTOH I'm looking at the 80287 datasheet, pin39 CKM controls the internal frequency divider. Logic high selects 1:3 divider, logic low disables divider and uses external clock directly. Guess a logic level tester and oscilloscope will answer the question, but first I need to find an ISA video card (I know I have a spare somewhere). :)
 
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I would bet you can expand this thing past 1mb too, maybe not on the board, but an ISA expander card with fast enough ram would probably work.
 
jh1523 said:
Possible, if I can find one that both:
1. is compatible, and
2. doesn't cost hundreds of $$$ :D
Click to expand...
Since this thing is only 16mhz, I would bet an AST Rampage meant for a later 286 would PROBABLY work, since RAM speeds would be very similar, now granted you probably wont get it up to more than like 4mb, but it beats 1mb. Something like an AST SixPak/286 (meant for 286's up to 20mhz) or AST Advantage! (may have issues with a CPU at 16mhz, meant for 8mhz ATs) card might work. Biggest thing to check would be how fast the ram on board is, I want to say even my OLD "Advantage!" card is using 120ns chips which would probably be norm on a early 386 like that. Pretty sure my SixPak/286 is using 100ns SIMMS.

If you keep your eyes out, you can find the AST cards for sub $30, I got 2 of mine in a $20 "lot of isa cards"
 
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If the board is populated with 256Mbit RAM chips might it not be possible to replace them with 1Mbit versions to expand the motherboard's RAM to four megabytes? That should perform somewhat better than RAM in an ISA slot. The picture of the board is too tiny for me to tell definitively but it looks to me like there are empty holes in the populated sockets which would allow them to accommodate replacement chips with more pins.
 
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