• Please review our updated Terms and Rules here

ISA cards don't make contact with motherboard in my AT cases (486 motherbaord)

Overmann

Experienced Member
Joined
Apr 21, 2017
Messages
102
Location
Norway
Hi there,
So I've been having an issue. I have a 486 build that I'm trying to put together but I can't find a case that fits. It's a regular AT motherboard and all regular cards, but the motherboard always seem to end up sitting too low in the case. It's the bracket on the ISA cards that make solid contact with the backplate BEFORE the ISA cards themselves are properly socketed in the ISA slots.
I've tried two different cases now and I have the same problem in both. I've tried both cases wth a 386 motherboard and while the ISA cards are not ALL the way in, the make comfortable contact. The standoffs are 5mm or thereabouts. Regular PC motherboard standoff height. One case came with AT plastic standoffs but they were the same height.

Has anyone else had this problem, and are there any known, good solutions? I have been looking around for taller standoffs, a couple of mm would probably make a build possible, but I can't find those floating AT standoffs in any other height then the regular 5mm'ish so I would need replacement, which would meem having standoffs with enough "screwside-length" to use a bolt on the backside.. It's been a frustrating couple of months trying to put this thing together and I've just had a bit of a soul-killing experience so I thought I'd ask here if anyone has any suggestions.
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
5,099
Location
Upper Triassic
Are the ISA slot connectors on the 486 board shorter than the ones on the 386 board? That would be... kind of weird.

Assuming the standoffs you're talking about are the little hexagonal ones (usually brass colored, but sometimes silver) I definitely remember them coming in two common heights and 5mm sounds like the shorter of the two. (I checked my Altoids can-o-PC screws and unfortunately I'm down to only two of what I remember being the shorter ones, but my vague recollection is the most common sizes are "around a quarter inch" and "closer to 3/8th inch" long. The ATX 2.1 standard calls for minimum 6.5mm standoffs, I assume they probably based that on the most common AT sizes.)

It's stupid, but I'd probably suggest your best route might be to "dry fit" a couple ISA cards snugly into the slots on the motherboard, get the brackets onto the backplates, and measure how long of a standoff you need. Actually ordering some of the correct height shouldn't be too expensive.
 

Overmann

Experienced Member
Joined
Apr 21, 2017
Messages
102
Location
Norway
Thanks for the suggestion! I've been experimenting with nuts and bolts etc. today and I think I might have managed to get things level so that all the cards make good connection. One large nut, one small nut and four metal washers was the correct distance. More made the keyboard plug on the MB impossible to reach from the back of the case :p

Now I suddenly have a completely different problem: My HDD doesn't work with the 486 working in 66mhz mode.. Well, It's all part of the fun I suppose :p
 

MikeS

Veteran Member
Joined
Dec 23, 2005
Messages
7,493
Location
Toronto ON Canada
The barrels from dried-out ball point pens are a good supply of spacer material and they're insulated, so no risk of shorting the PCB to the chassis.
 
Top