Zarcon Dee Grissom's Idea Page
EV9
Updated 02NOV2007
Home > Meet the computers > OSWATT > OSWATT XT2ATX 
OSWATT, "O" Censored, What Are They Thinking!

Not so much OSWATT today as when OSWATT was built in 2004/2005. However there is still some very cool guts and ideas implemented in this XT/AT converted case. First and for most is it's shear size, they don't make cases this big any more. Second is it's lack of noise, even with everything going full tilt. And then the cool guts.
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Warning.
1> I Will NOT be responsible for anyone being stupid and operating dangerous power/non-powered tools they do not know how to operate safely, and causing damage to themselves and/or equipment in the process. RTFM!
2> get all the metal shavings out of the case with a shop-vac, and compressed air, before you bring the case any where close to the final working electronic guts. the drilling and cutting shavings will do nasty things to your expensive electronic parts. they'll even destroy some vacuum cleaners.
3> Metal shavings can destroy vacuum cleaners, Don't test your eyes resilience to them. Ware safety goggles certified for metal work.
4> Sharp edges will make nasty cuts, requiring trips to the emergency room for stitches. Ware thick leather gloves, preferably Welding gloves when handling sheet-metal, and watch where BOTH your hands are at ALL times.
5> Ask many questions, do lots of research, measure allot, test on stuff you don't care about first that you own, and hesitate to cut and drill the final project.
6> And last but not least. I will not be responsible for how good or ugly your computer-mod, or any other project inspired by my sight, looks, function, or fails.


XT/AT2ATX mod intro.
Baby-AT, AT, AT2ATX, ATX lineup
baby-AT, AT, AT2ATX, ATX
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AT2ATX inside
View of cut off PCI coverplate
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Note the cut off PCI cover plate on the eighth PCI slot on the converted case. This is optional for sealing the case if it only has exhaust fans. I find with intake fans on the front of the case, it's better to leave the mutilated slot open for extra exhaust.

I'll start with the XT/AT to ATX mod. The case was given to me (Thanks to Bronsen for the case), when I was looking for a tower to house my next workstation. I got tired of not having room for more hard drives, lack of proper air flow making the case ventilation noisy, etc. this case was almost everything I was looking for. 27 Inches tall, 18inches deep, and 8.75inches wide, and not a file cabinet on coasters. The case just was not ATX compatible, yet.
back I/O panel
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mobo mounts
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Well it was time to cut out the back panel, and drill and tap the five missing Motherboard mounts. Then I sat down and stared at the case for a wile, drew it up on graph paper, and sketched out some ideas. I Needed to put fans in to cool the guts, however I wanted them to be silent. Then I remembered the bandpass woofer box design. The noise maker sits on a baffle in the box, with tuned ports that resonate at a low frequency. This case is big enough to make it resonate at a lower frequency then any fan in it. The large side panels needed to be stiffened to prevent them from acting like speaker-cones. The last trick is to make sure the intake vents, exhaust vents, and air path threw the case are large enough to prevent any whistling affect. That included the hard drive racks.
OSWATT prebuild scetch
(OSWATT Case draft 1001x632)


XT/AT2ATX mod basics.

The back panel mod.
I/O panel size
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LAB2 I/O panel
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Some back panels are not usable, others are good to go. The back needs to be indented from the seventh PCI/ISA slot up another six inches for the Motherboard I/O panel and cover plate. This six inches starts at the lower edge of the eighth slot, and extend upward towards the power-supply (PSU) opening. If there is not enough room for this I/O panel between the eighth expansion slot and the PSU opening, game over for that case, unless you want to try to make it a Micro-ATX. I don't think it is worth the trouble of machining a motherboard tray to drop in place of the old one for a foot-rest. If you don't care about the cover plate, then the case dose not need to be indented across the entire I/O panel aria, however there still needs to be room for the motherboard, and power supply.

The motherboard tray mod.
ATX Motherboard (MoBo) Mounts
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Most full size XT/AT motherboard trays have ALL the correct mounting holes, in the right places except the one behind the PS2 plugs on most ATX motherboards. You could get a protractor, and measure mills to mark the right placement for this and any other missing holes. I used a dead ATX board and a sharpie marker. After I cut out the back panel, I mounted the dead board in with what mounting holes that did line up, and inserted a couple dead PCI cards to double check the alignment of the PCI slot openings, and I/O panel opening. Then I dabbed the sharpie threw any holes that did not have mounts under them. Remove the dead board before drilling and tapping. Drilling and taping the new holes can be very tricky. if all else fails, use a spare standoff as a nut to hold in the new standoff. then ReMount the dead ATX board with dead PCI cards using ALL the mounts, to double check that everything will work for the expensive new stuff.
MoBo mount fix
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The above is from LAB3's Motherboard tray. I lost the slide-in plastic stand off for the mount in the foreground (left side of pic), and the hole tap stripped out rather then threading in on the drill press for the mount directly behind the PS2 plugs (right side of pic).

The Power supply Panel
PSU adapter mounting plate
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PSU adapter mounting plate
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PSU adapter mounting plate
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If the case has a Baby-AT PSU opening, you needn't bother modifying it, an ATX PSU will “Drop in” as if it was meant to be there. The exception is if you need to move it up or down for other parts. I cheated, I had Scott simply cut out the PSU section from another case and bolted it to the tower where I wanted the PSU. I intentionally placed the ATX PSU upside down in this case to prevent it from fighting the CPU fan for AIR. The end result didn't make as much of a difference for either the PSU, or the CPU HSF as I thought it might have. despite the lowest Hard drive being rather close to the PSU intake for my comfort, it still works great.

OSWATT gon ATX back
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OSWATT gon ATX guts
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The XT/AT case is now a modified ATX case.


XT/AT2ATX mod Extras.

The fan baffle and intake section
note, the Zalman probably wont work on your A8N-E board, I got lucky and it posted with the RAM pushed over slightly.
Fan Baffle front
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Fan Baffle back side
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Originally this case had a hard drive rack and a single 80mm intake fan on the front. those (as Scott quotes) got deleted.

The baffle that holds the 120mm fans is bolted at the bottom of the case only, and is held in by weather-stripping friction under the CD-ROM rack and sides. the baffle is just a piece of sheet-metal purchased from a hardware store, cut like a cardboard box at the edges, and folded over. the fans are held on to the panel with bolts, rubber washers, and nuts. the coat-hanger wire clips were an after thought to keep wires clear of the air path as best as possible.

Before any metal was cut, I measured where I wanted the fans. I considered where they wouldn't get in the way of the cards, cables, motherboard parts, and placed so the air would flow where I wanted it. then I traced out a template on paper, and handed it to Scott with the sheet-metal.
Fan Baffle front closeup
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Scott used a car mechanics cutoff wheel to make the octagon shaped fan openings, and a regular drill for the fan mount holes. After using an air-fitting to clear off the metal shavings and dust outside, I mounted the fans to the panel. I placed weatherstripping around the fans to seal the seam between the fans and the panel. then I put weather stripping on the upper three edges of the panel to seal the seam between the panel and the case. some where along the way, I got carried away with the weatherstripping, and covered the entire panel except where the fans were and the bottom edge. I can never have enough sound dampening.

Intake,
Following the first order of Laminar fluid flow as described by the Navier-Stokes equations, bla bla... 
hu, what was that?cross-sectional areas of the flow and the volumetric flowrate Q,eyes glossing over
My eyes glossed over about there. time for a simple approach to air flow.
Intake Vent
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I measured the size of the 120mm fan opening (about 4.7244in), and calculated the circular aria of the fan opening with a web-page-calculator (17.530 square inches ). I then decided that the intake hole in the front and the exhaust in the back of the case needed to be at least twice that big for the two 120mm fans not to whistle, at least 35 square inches (8+ x 4.375+ inches). so in short I needed almost the entire front bezel below the CD-ROMs, severely weakening the case with the sides open. there are five CD-ROM bays, I only need four. I'll steel the lowest one as part of the intake.
Not so secret intake
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with that additional 5.85 x 1.7inch roughly 9.945square inch intake, I had room left below for an "S" shaped airflow silencer that hasn't been implemented yet, and some structural reinforcements for the case. If you don't have it here, barrow it from over there. I think that is call the Harley-Davidson-"V"-rod-secret-volume(tm) affect. 

Case reinforcements
When the case weighs over a hundred pound empty, one rely needs to consider the foundation and sub frame that supports the tower. Sheet metal is only so strong, even the thick 3/8" steel sheet metal will buckle under it's own weight without a reinforcing structure.
Front bracing
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I grabbed some Aluminum trim peaces from the metal rack at the hardware store, OK I stand corrected. Scott states, I purchased the entire rack. I cut the trim pieces to length in a vice with a hacksaw, used mini-C-clamps to hold them in place while I drilled holes for there mounting bolts. I uses "8-32" bolts of various lengths to bolt everything together. the 8mm bolts seam to fit most fans, and I wanted everything to be interchangeable.
left panel bracing
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right panel bracing
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the side panels were braced in a similar way. however I marked them with a sharpie where they came close to stuff in the case first. I didn't want to brace them, only for the braces to prevent the side panels from closing completely. I only had one shot with this case. Getting a replacement case, and starting over was not an option. Like I wrote at the beginning of this project follow up, they don't make big cases any more.

Upper HDD rack
I needed to make something to hold the hard drives, and at this point I new the graphics cards of choice would need bracing for the Flatscreen2VGA adapter things. I let the DVI2VGA bracing thing ferment in the back of my mind, as I sat down and started making an "L" channel open frame hard drive rack. Remember that air flow thing, and not whistling. having an open frame hard drive rack is a simple way to allow maximum air flow between the drives.
Open-frame HDD rack back
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Open-frame HDD rack front
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I do have pieces of zip-cord with eyelets soldered onto the ends to help ground the drives in the rack, I got lazy with attaching them.

The rack is actually quite simple, there are four upright "C" channel beams, holding the "L" channel Hard drive slides. some weatherstripping keeps the hard drives in place, and dampens there noise. I used simple "L" brackets to mount the rack sides to the top of the case.

Lower HDD racks
notes for others. "O" god, the pealing paint is ugly, I should have sanded that first... 
Lower HDD racks
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Lower HDD racks
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I love that spare room below the motherboard. the lower hard drive racks are leftovers from other cases. I drilled holes in them between the drives to allow air to get threw the mess easier. mounted the drives in them, and set them in the case. no mystery bolts or clips under them, there just sitting there.

DVI2VGA bracing
DVI2VGA brace
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DVI2VGA brace
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I didn't want the weight of the monitor cords combined with the excessive length of the adapters putting unnecessary stress on the graphics cards, possibly breaking the graphics cards at the plugs. I took some sheet metal and bent it to about the height of the PCI panel, then bent it to about the length of the adapter from the back of the computer, and then set it aside for final assembly. I was going to cut out the plugs and adapter standoff holes in the brace. the monitor cords twist tabs things would mount threw the brace to the adapters, firmly securing that part to the brace. the part of the brace against the case is held to the case by the side panel screws, and the expansion slot panel screws. the brace is cut behind the slots to allow it to support both upper and lower graphics cards monitor adapter plugs. in the end I just folded the upper card slots over for the adapters to rest against the brace.


Afterthoughts

foam stuffed in between CD rack, and motherboard tray.
Tape and foam
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tape and foam2
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I did this to prevent the fans from sucking hot air from the top of the case back down and re-cycling it back across the motherboard. I thought about making a piece of sheet metal to fit in this spot. I've been rather distracted from the little details of the case, and the foam is working quite well.

duck-tape on motherboard tray.
Again this was to prevent the fans from re-cycling the air. the duck-tape has worked to date. I forgot it was there until I opened that side of the case up to photograph it. I hang my head in shame over that, it was originally a test to see if the holes in the motherboard tray affected the case temperatures.

Computer Case Station Grounding.
Pulling out a Gront-strap on RFI
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You may notice that ugly copper pipe behind the desks with wires hose-clamped to it, that is an RF ground buss. Every single computer in here is strapped to that with heavy short cables (8AWG or better). for a complete description of station grounding, refer to the ARRL Amateur Radio Handbook chapters on Station Safety and Grounding, and the up to date NEC Hand Book. The picture above is 6AWG with two eyelets on the PSU, I don't take RFI lightly when it affects my 2m-radio or my di.fm experience.


Future ideas and plans for this case.
1) make a permanent solution for the duck-tape on the motherboard tray.
2) make a baffle that forces air between the expansion cards. I don't know how much air is going right past the cards, and out the back of the computer. I imagine it is a substantial loss of cooling potential. Maybe another HDD rack the entire height of the motherboard tray on a hinge there.
3) adjust the upper hard drive rack, to allow the PSU to breath better. that also includes my dislike of having magnetic storage right next to a motor.
4) figure out where to add a support brace on the back of case next to the expansion cards, without obstructing the exhaust vents or the side panel hinge.
5) I was going to place an 8 gage power distribution system in the case with RFI filters for each drive and fan. The parts list for that project is still yet to be drafted out. I have a couple filters sketched out already, none production/prototyping ready.
6) make a plate to hold the power button in the original switch spot. then place a ring key in series with the button where the button currently is. the idea is, if the key is not in the case, you are not going to shut down the computer.
7) remove the Motherboard to replace the dead chip set cooler. it would have been nice if one of the big holes in the motherboard tray lined up with the clips under the cooler. "O" well, that ugly 486 fan is working well enough.
8) Fix the pealing paint, and paint the front grill red to finish the CRAY2 look.
9) build that Burr-Brown headphone amp, I've been wanting to build for three years now... lol.

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