The Mother Board

evasive · Posted: Thu Jul 19, 2012 12:30 am Post subject:

@8bitbubsy: do you have a 5V CPU to test with? DX33 if possible? That way if you set the bus speed to 33 it will at least boot and we can work from there.
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8bitbubsy · Initiate Joined: 28 Sep 2011 Posts: 30 Location: Norway

I have a 486DX66, it doesn't POST with it either. Also I have no clue where to set the bus speed, I've tried many different combinations of the jumpers near the CPU, no nothing. Not even a beep from the internal speaker (I have put the jumper on the speaker header so it's enabled). Tried different combination of SIMM modules, in different orders and so on.
I don't get a sync signal from the internal video card, I even tried a PCI video card, no sync at all.

Ok here's the full story so you won't get confused:
I found this machine outside of an electronics store, they receive old electronics that goes to the dumpster. I took it home and fired it up, but the PSU was dead. I have yet not found out what's wrong, the fuse is OK, start-up resistors are OK etc (this is another topic).
Then I tried a bog-standard 486 AT PSU, and it booted up. It had a DX4 100 installed. I had another 486 back then so I didn't care more for this machine because any AT PSU would not fit inside the small chassis. Some years later I eventually started to take jumpers from the mobo because I needed them in another system, that's how I messed up the mobo in the first place...

Well here I am, trying to revive it from its death. I really want a nice 486 system for nostalgic reasons, also it's one FAST 486 system or what not.

Oh, not to mention that it's one rare piece of a 486 motherboard, so I want to contribute whatever I can find on it. It's kind of exciting!

evasive · Posted: Thu Jul 19, 2012 1:04 am Post subject:

I see... In that case I think you will have to go one step deeper and find where the jumper traces are going and match the pins on the CPU with its function and make an educated guess on the function of the jumper block. Another option would be to compare other 486 boards made by ASI, there is a remote chance they have copied the jumper settings layout between board, although that's rare in that era, as board space was scarce...
_________________
We hate rut, but we fear change.

System error, strike any user to continue...

8bitbubsy · Initiate Joined: 28 Sep 2011 Posts: 30 Location: Norway

I have already checked all the other ASI boards online, the jumper configuration doesn't match the least.

Karlsweldt · Posted: Thu Jul 19, 2012 9:11 am Post subject:

Some of those jumpers configure the cache type and amount, others the core and I/O voltage, bus speed and multiplier.. as well if the CPU is an "SX" or "DX" type. The suggestion by evasive to use a plain DX33 type may show some life signs.
There are hundreds of old 486 mobo models listed on eBay.. but nothing close to this one in design. That single slot is the crossover ISA/VESA design. Dell, AST and other brands had similar boards, but not the same layout as yours.
Without a pinout diagram, it will be frustrating to "trace" the circuits.. so here is a link for the 486 CPU pinout.. with functions! http://pclinks.xtreemhost.com/486pin.htm
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8bitbubsy · Initiate Joined: 28 Sep 2011 Posts: 30 Location: Norway

Karlsweldt · Posted: Fri Jul 20, 2012 4:48 am Post subject:

No offense meant in those suggestions as to other routes to explore. While you may have good knowledge of computer design and workings, others who view this post may gain some knowledge.
In a situation like this, I rely on a POST diagnostics card ( eBay link ) to display a code as to the probable fault. But in your case, you would need an ISA-type model, plus the riser card for that motherboard.
And from past experience with those designs, some require the riser card to be installed before life-signs are present! That particular motherboard may only have ISA card features, but possible it also has PCI card features. The first PCI 1.0 version device card slot appeared in 1992. Design of that version was started two years prior. Since some chipsets on your board are dated to 1995, very possible.
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F@H.. to solve mankind's maladies.. in our lifetimes!

8bitbubsy · Initiate Joined: 28 Sep 2011 Posts: 30 Location: Norway

Yeah, I always have the slot riser in when testing the system. It has 2x PCI and 2x ISA, also the ones you linked to on eBay is for both PCI and ISA (you can turn them around, look at the picture).

Anyhow, thanks for the suggestion, I'll definitely buy one of those. If it doesn't help me here, it might help me another day on another computer. lachen

Twisty · Posted: Fri Jul 20, 2012 1:35 pm Post subject:

Karlsweldt · Posted: Sat Jul 21, 2012 5:09 am Post subject:

Auto-sense only in the means of showing the CPU speed and type. The 3.3 volt only CPU types had an extra pin, so it could not be inserted into the 5 volt only socket. The DX2-50 and DX2-66 5 volt class had internal regulators and clock doublers. The Intel "Overdrive" types were 3.3 volt class.. with the extra keying pin. For 'upgrade' CPU types, you had to set jumpers on the board.. or fry the CPU. The Socket 5 and Socket 7 types also did not have auto-sense as to setting the core/IO voltage levels. That came to be with the Socket 370 series and Slot 1/Slot A series.
Here is another link to processor socket types.. with pinouts.
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F@H.. to solve mankind's maladies.. in our lifetimes!

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