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AT Power Switch Wiring

Zane68
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I have an AT power switch hooked up to my retro '93 PC, and when I press the switch, the PC spins to life. I get lights, I get fans, but it seems everything but the main components of the motherboard are working. I'm not getting display, yet my old ATI graphics card gets warm after a bit, and my hard drive spins up. I don't even get a BIOS beep. I see other people have black, blue/green (what i have) but then they also have brown and white wires that I don't have. Im wondering if this is the problem as I don't know what those wires are for. Also I'm using an Ultra 550w PSU (ATX 24/20 pin) and an adapter to use P8 and P9 connectors for the motherboard.

 

Anyone have any ideas?

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you might need -5v for your specific board, and an atx power supply doesnt have that, unless the adapter has a converter built in.

 

perhaps a full list of specs will prove useful here.

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14 minutes ago, manikyath said:

you might need -5v for your specific board, and an atx power supply doesnt have that, unless the adapter has a converter built in.

 

perhaps a full list of specs will prove useful here.

Yeah i don't know if the adapter had a -5v regulator or not. I just assumed it had it.

PC Specs:

 

AM386/486 motherboard

4x256m 30 pin SIMM

ATI Small Wonder Graphics Solution Ver.2 64Kb VRAM 640x200

Soundblaster AWE64 100% Compatible Clone

Quantum Fireball 15Gb Hard Disk

Drive A & B 

Ultra 550w PSU + a test Power Man 330w PSU

 

Hope that helps

yhst-39083765508394_2271_309582791.jpeg

IMG_20220527_104340.jpg

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1 minute ago, Zane68 said:

Yeah i don't know if the adapter had a -5v regulator or not. I just assumed it had it.

PC Specs:

 

AM386/486 motherboard

4x256m 30 pin SIMM

ATI Small Wonder Graphics Solution Ver.2 64Kb VRAM 640x200

Soundblaster AWE64 100% Compatible Clone

Quantum Fireball 15Gb Hard Disk

Drive A & B 

Ultra 550w PSU + a test Power Man 330w PSU

 

Hope that helps

do you have an AT supply, and does it work with that AT supply?

 

past that... if the adapter doesnt have an obvious board or box along it's length.. it doesnt have -5v

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2 minutes ago, manikyath said:

do you have an AT supply, and does it work with that AT supply?

 

past that... if the adapter doesnt have an obvious board or box along it's length.. it doesnt have -5v

I do not have an AT power supply. just a few windows XP era ATX ones.

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41 minutes ago, manikyath said:

do you have an AT supply, and does it work with that AT supply?

 

past that... if the adapter doesnt have an obvious board or box along it's length.. it doesnt have -5v

Also why does the -5v thing matter to the PC?

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1 minute ago, Zane68 said:

Also why does the -5v thing matter to the PC?

some motherboards (and some ISA cards) use -5v for some logic IC's no -5v means those logic chips wont work.

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5 minutes ago, manikyath said:

some motherboards (and some ISA cards) use -5v for some logic IC's no -5v means those logic chips wont work.

Thank you, everyone else gives these very complicated answers. yours, i could actually understand. I think this is probably the problem. I'll pick up an AT PSU sometime soon

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52 minutes ago, manikyath said:

some motherboards (and some ISA cards) use -5v for some logic IC's no -5v means those logic chips wont work.

Just a quick video I made for youtube on the situation:

 

(accidentally called p8 and p9 connectors p1 and p2)

 

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4 hours ago, Zane68 said:

Just a quick video I made for youtube on the situation:

 

(accidentally called p8 and p9 connectors p1 and p2)

 

try and figure out which motherboard that is, maybe that'll be of some help.

 

on that note, have you had this computer in working condition at all, or is this a revival project?

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7 hours ago, Zane68 said:

Also why does the -5v thing matter to the PC?

Not having -5V won't prevent the PC from posting.

 

Can you link to the ATX to AT adapter you're using?

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23 hours ago, manikyath said:

try and figure out which motherboard that is, maybe that'll be of some help.

 

on that note, have you had this computer in working condition at all, or is this a revival project?

My dad had this PC working back in the 90s, and he took out the board and put it in a box until I discovered it a month ago. It worked fine when he took it out of it's original case. The motherboard is called am386/486 dx40. I found the manual once, then lost it. there are two CPU sockets on the board, one for a 486, and one for an am386 dx40

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Both PSUs are quite old.  Are we sure they're in functioning order?

 

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21 hours ago, jonnyGURU said:

Not having -5V won't prevent the PC from posting.

 

Can you link to the ATX to AT adapter you're using?

My current adapter:

https://www.ebay.ca/itm/313976715163?hash=item491a78779b:g:vHsAAOSw~kBc3jFf

 

In old power supplies, there were 4 wires. Black, Blue, White and Brown. I only have blue and black. Is this a problem?

 

by the way, if my lack of -5V happens to be the problem, would this help?

https://www.ebay.ca/itm/174744918558?hash=item28af9bda1e:g:5-0AAOSwhaFhJPyB

 

 

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1 minute ago, jonnyGURU said:

Both PSUs are quite old.  Are we sure they're in functioning order?

 

Not old enough I'm afraid, they have -12V like a modern PSU.

 

my 550w sometimes makes weird sounds, the 330w sounds fine, both their fans spin. Last time they were used, they both worked.

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5 hours ago, Zane68 said:

Not old enough I'm afraid, they have -12V like a modern PSU.

 

my 550w sometimes makes weird sounds, the 330w sounds fine, both their fans spin. Last time they were used, they both worked.

No... That's not my point.  Even 20-pin ATX has -12V.

 

I mean, the shelf life of unused PSUs are not very long.

 

If capacitors sit for a long time without voltage to them, the dielectric oxide layer can start to deteriorate. The dielectric oxide layer reacts with the acidic electrolyte and the oxide layer breaks down. As the dielectric layer starts to deteriorate, leakage current will increase when rated voltage is applied. This high leakage current flowing through the capacitor with the deteriorated dielectric can destroy the capacitors.

 

It's really not that much different than "old batteries" leaking.

 

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16 hours ago, Zane68 said:

My dad had this PC working back in the 90s, and he took out the board and put it in a box until I discovered it a month ago. It worked fine when he took it out of it's original case. The motherboard is called am386/486 dx40. I found the manual once, then lost it. there are two CPU sockets on the board, one for a 486, and one for an am386 dx40

it's not because it worked 30 years ago it'll suddenly work now.

 

i've been trying to dig up which board this is, havent quite pinned it down, but all of the ones i find have the leaky batteries that love to ruin stuff.

 

i'd check around the battery for corrosion, and go from there.

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49 minutes ago, manikyath said:

it's not because it worked 30 years ago it'll suddenly work now.

 

i've been trying to dig up which board this is, havent quite pinned it down, but all of the ones i find have the leaky batteries that love to ruin stuff.

 

i'd check around the battery for corrosion, and go from there.

The Soldered CMOS battery does have some corrosion on one side of it. I noticed this as soon as I looked at the board. There isn't much corrosion, so I didn't think that was the problem.

 

This is an image of someone else's am386/486 board. The exact same as mine:

Generic M321 REV.2.5 Motherboard AM386 DX-40 Chip | RecycledGoods.com

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17 hours ago, jonnyGURU said:

No... That's not my point.  Even 20-pin ATX has -12V.

 

I mean, the shelf life of unused PSUs are not very long.

 

If capacitors sit for a long time without voltage to them, the dielectric oxide layer can start to deteriorate. The dielectric oxide layer reacts with the acidic electrolyte and the oxide layer breaks down. As the dielectric layer starts to deteriorate, leakage current will increase when rated voltage is applied. This high leakage current flowing through the capacitor with the deteriorated dielectric can destroy the capacitors.

 

It's really not that much different than "old batteries" leaking.

 

I don't think two PSUs could go bad like that. one was working 17 years ago and was barely touched, so that one MIGHT be bad. The 330w one however, was used about a month ago and worked perfectly. Either the problem with my PC is the corrosion on one side of the CMOS, or it could be the wiring on my switch or maybe the -5V.

 

Thanks for the help!

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