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AST 486/33E Won't Post

Joined
Jan 15, 2015
Messages
205
Location
Hebron, Boone Township, Porter County, Indiana, US
Power supply was dead so I used an AT replacement however the computer won't post. someone ****ed with the jumpers on the board so I put them all back to factory according to the manual i found online. damn thing still wont post. no beep codes or anything. if i cannot get it running I am going to use a generic 486 motherboard and build my own 486 into the case
 

mR_Slug

Veteran Member
Joined
Nov 28, 2006
Messages
874
Location
UK
Joined
Jan 15, 2015
Messages
205
Location
Hebron, Boone Township, Porter County, Indiana, US
I determined PSU was dead because it wouldn't power up. I am sure it is 100% AT Compatible, because the pinouts for the motherboard connector are listed on the power supply label and match the AT spec. I only have one ISA video card and that is the one in this unit, I suppose I cant rule that out, but if it was in fact a bad video card I think id still hear it booting, checking the drives, beeping et cetera. I did notice that the motherboard does not have a CPU or RAM Sockets, these are on a giant VLB card that take up one of the VLB slots. How's that supposed to work? A CPU and RAM as an add on card? I simply cannot figure out what is going on here, why it won't post. If I dont make any progress soon, I'm gonna take the mobo out and build a 5170 into it.
 

mR_Slug

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Joined
Nov 28, 2006
Messages
874
Location
UK
I only have one ISA video card and that is the one in this unit, I suppose I cant rule that out, but if it was in fact a bad video card I think id still hear it booting, checking the drives, beeping et cetera.

Have you tried powering it up without the video card?

I did notice that the motherboard does not have a CPU or RAM Sockets, these are on a giant VLB card that take up one of the VLB slots. How's that supposed to work? A CPU and RAM as an add on card? I simply cannot figure out what is going on here, why it won't post.

As far as I can remember this is an active backplane system. The card is not VLB. What you have is a very early EISA 486 system. Probably based around the Intel 82350 chipset. A passive backplane puts all the motherboard on an expansion card, and you just have slots where the motherboard would usually go. This puts some of the basic circuitry on the motherboard, and the CPU+RAM goes on the card. The idea was build a relatively basic motherboard, that you can upgrade easily by replacing the CPU+RAM card. Have you tried cleaning the card edge connectors on the CPU+RAM card? A pencil eraser often works, or fine sandpaper. Will an AT motherboard even fit? It sounds like you have quite a nice system. To me it's worth preserving it if possible, but I do have a soft spot for EISA systems.
 
Joined
Jan 15, 2015
Messages
205
Location
Hebron, Boone Township, Porter County, Indiana, US
There are VLB slots on the motherboard, and the CPU card must go in a VLB slot. why do you say to clean the card? I've never heard of that. I guess it is worth a shot. I'm going to also have to find a replacement AT power supply that has the switch in the back side instead of a wired switch. but that must wait until i get this damn thing to post
 

fatwizard

Veteran Member
Joined
Sep 28, 2012
Messages
525
Location
Indiana, USA
I have had so many cards benefit from cleaning the edge connector. Some weren't functional at all until they were cleaned. A pencil erasure is my choice for buffing out the contacts, and with a CPU?RAM card it would be all the more critical to have good connections. From the look of the layout on Stason.org, I would place the CPU/RAM card in the slot marked S1, as it appears designated for that purpose.
 

krebizfan

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Joined
May 23, 2009
Messages
5,338
Location
Connecticut
That works if you have a laptop using BGA connectors which basically float on a bed of solder. Heat solder and chip drops down into the solder. A more traditional soldered pin design probably won't be corrected that way. Need to apply new solder to each broken connection.
 

mR_Slug

Veteran Member
Joined
Nov 28, 2006
Messages
874
Location
UK
If this M/B has the quad-flat-pack style surface mount chips (square with pins all the way around) and you do decide to bake it, I would not move the board at all until it has cooled. If one of those slips out of alignment you will have a real nasty time trying to fix it.

Just to confirm:
Is the link I posted before, to the th99 spec sheet at statson, actually your board?
Is the PC speaker connected, and verified as working?
Have you cleared the BIOS?
When you turn on the PSU does the fan spin up normally or stall?
With the PSU on and M/B connected, do you measure 12v and 5v, at the PSU connections?
When you say screwed with the jumper settings, did you try with the settings it had originally?
What graphics card are you using (chip name)?
Do you have a POST diagnostic card?
Have you verified the RAM and CPU are working?
Do you have any pictures?
 

PeterNC

Veteran Member
Joined
Oct 6, 2013
Messages
2,694
Location
Miami, FL
Probably dead. Do not waste your time. OEMs are still relatively common and cheap. Spending lots of time and $ in diagnostic / replacements parts exceeds the fair market value.
 
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