Ok this is what I did. My pc power switch went out so I decided to go with a regular toggle switch and ended up tripping my breaker. I would now like to test the power supply on computer. Without switch connected could I check for 5v, 12v levels at mother board? Or do you think the second I try to plug up the power input to pc the breaker will just trip again. Whats a good way to check for this? Yes, I soon discovered that pc p.s. switches are not just toggle switches. What kind of damage is likely to have happened to computer.
("AT" 4-wire style power supply)

Yes, I soon discovered that pc p.s. switches are not just toggle switches. "AT" 4-wire style power supply)

I have always used regular switches, even a relay, I suspect that you have wired a double pole switch and got the connections wrong so that it is a dead short across the 120ac, test the input with a meter. it will be very low resistance but not as low as a dead short will show, compare the readings to your meter leads shorted (resistance scale). If this is what happened then you will have done no damage apart from maybe welding the contacts on the switch.
Al.

Thanks AL, I was told that the switches used for pc power made contact and then released not like a regular switch. So I see I could use this toggle switch? How should it be wired? Basically the original had a line to divide pins into "p1" and "p2". The new switch has tabs for four wires to be connected, but it is an on/off switch. I think the switch signals to a relay to tell power supply wake up. Are these tests, you spoke of, at the input to power supply?(ac volts in)

If I understand your question correctly, you hot wired the push-button power switch on the front of your computer case...
(nothing wrong with this).. The switch is a MOMENTARY CONTACT only type.. As you said in your post above..
I am not sure what would happen if you closed the switch and left it closed.. Honestly, my best guess is that the computer would keep rebooting continuously unless there is a circuit to prevent it..
If you had a continous contact, and the computer went down after a bit, that would scare me into thinking your mother board is toast..(But I dont see any reason why to be honest).

I have a large control box.. 6ft tall x 3 feet wide x 3 feet deep.. My computer case is inside that box and I just ran a sheilded pair of wires (in parrellel with the front panel switch) to an allen bradley push button that is mounted on the panel box.

It has worked perfectly ..

I doubt your power supply is bad.. If something did go bad, I'd check the mother board.

Murphy

The later ATX supplies have the ac power to the supply as soon as the computer is plugged in and there is a momentary push button switch on the front that grounds a low voltage signal line and the computer motherboard turns on. The early supplies had a double pole switch on the incoming AC, so if that is what you have, you can easily check the switch with a meter, there will be 4 connections and each pair will close when on, then identify the incoming AC pair and connect each wire to one each of the pre-identified switch pair.
Al.

Thanks AL, I was told that the switches used for pc power made contact and then released not like a regular switch. So I see I could use this toggle switch? How should it be wired? Basically the original had a line to divide pins into "p1" and "p2". The new switch has tabs for four wires to be connected, but it is an on/off switch. I think the switch signals to a relay to tell power supply wake up. Are these tests, you spoke of, at the input to power supply?(ac volts in)

Your computer should only have 2 wires that need to be momentarly closed.. The other 2 wires are probably for the LED light..

Check your mother board schematics (users manual).. it will tell you which pins on the header are for what...

Murphy

Your computer should only have 2 wires that need to be momentarly closed.. The other 2 wires are probably for the LED light..


It all depends on wether he has a ATX computer/supply the older ones actually switched the incoming AC.
Al.

It all depends on wether he has a ATX computer/supply the older ones actually switched the incoming AC.
Al.


Oh.. Ya. I forgot about those old ones.... Are they still around??
I have not seen that type for sooooo long... mmmm 10 years at least??

Do people still use these??? That was the old 80386 days wasnt it?

Murphy

Actually I tore down the original switch. Its not functionable anymore. So if I understand, I can use the toggle switch to connect to 2 of the 4 wires possibly? And to find out which 2 to use would be the 2 that send a signal to the mother board? On an earlier test 2 of the 4 wires read around 110 volts ac, and the others read around 8 volts I believe. I'm trying to determine which 2 I could connect to the new toggle switch. definitely an "AT" style supply.

Do people still use these??? That was the old 80386 days wasnt it?

No, Right up untill the early pentiums 500mhz or so.
Al.

thats right, its a 450 mhz. mystery box.

Actually I tore down the original switch. Its not functionable anymore. So if I understand, I can use the toggle switch to connect to 2 of the 4 wires possibly? And to find out which 2 to use would be the 2 that send a signal to the mother board? On an earlier test 2 of the 4 wires read around 110 volts ac, and the others read around 8 volts I believe. I'm trying to determine which 2 I could connect to the new toggle switch.

Obviously you have the AC switched version, the original is connected as a double pole, if you want to connect as single pole? then you will have to identify the incoming AC usually black and white and the two to the supply was blue and brown. If connecting as a double pole switch, then the black and white go to the switch pair I outlined in the previous post, and the blue/brown the other side of the pair. If you want to connect as single pole then the black and blue are switched and the brown and white have to be permanently wired together, It is important to identify every conductor and switch contact with a meter, if you are having a problem in that area, I would get someone to help you.
BTW you do NOT send a signal to the mother board on your version.
Al

Thanks for your patience, I'm enjoying learning.

http://www.pcguide.com/ref/power/sup/partsSwitch-c.html

From reading all the posts the only argument is if the switch can be an on/off type? (non momentary) sounds like it could be.

If your PC uses an on off switch at the front like the link above shows its an AT PSU and the switch is an On/Off switch - that is a two pole two throw switch. The momentary switches only work with ATX psu's.

The give away is that there is 120vac on the switch, so therefore this definately rules out ATX (momentary).
Al.

AH, I understand. I guess now we have definitely cleared up this topic. Thanks again

Guys, I seem to be a bit late to the party, hope this would be helpful --

To tell an "ATX" supply from an older "AT" suplly, trace a cable that goes from the PS to the motheboard. Do not disconnect the connectors - just look it up, the differnece is too huge to miss. The "AT" PS connects through 2 single row connectors, arranged side by side:

[o o o o o o][o o o o o o]

There are no white, grey or green wires. There are few black (ground), yellow (+12V), red (+5), and 2 other wires of distinct colors each (I do not remember colors)

You can even think this is one long connector. I think there were 6 pins on each. "ATX" ends with a large single 2-row connector, there are 2x10 and 2x12 pin varieties, and you would have a thick cable containing all rainbow colors and a few not found in nature :)

[o o o o o o o o o o o o]
[ ]
[o o o o o o o o o o o o]

All ATX supplies work the same way: they turn on and off when seeing a low-voltage control signal (the green wire. Connect it to any black ground wire, it comes on; disconnect and it comes off). This way, a computer can turn off itself, or switch to a low-poer mode etc.

What we came to call "AT" PS were not standardized, and powering up and down was the business of the PS alone. However, I have not seen any electronic switches - anything other that your garden variety AC-breaking switches.

Look at the cable that goes to the switch. Consider was it engineered for harmless control voltage, or for line AC. If it has 4 thick (16 AWG or thicker) wires, enclosed into a rubber jacket, you definitely see AC wires. If it consists of a few thin wires (much thinner that black-red-yellow wires conibg out of the PS!), tied together with cable ties or like, this is definitely a control line.

Most likely you have an AC switch. Now Al, let me please disagree with feasibility of that test:

The give away is that there is 120vac on the switch, so therefore this definately rules out ATX (momentary)

This test is too dangeerous, and not necessary. Instead, find which 2 of the 4 wires connect to prongs of an AC cord connected to the PS, disonnected from mains, of course, using a continuity tester. There are 4 wires total. 2 of them go from the outlet. Each of these 2 is connected to one of the prongs. 2 other are AC input of the PS.

<--------------------------------------> <--------------|----
From AC the 4 wires to switch To PS guts
<--------------------------------------> <--------------|----
If you have no multimeter, make a continuity tester from a 1.5 to 9V battery,
a matching small lamp and 3 pieces of wire. (If you want to test continuity in lines with semiconductor devices connected, then go 1.5v only)

Now we have that hot-vs-neutral problem, but I do not think that there is a way to find out which where is expected by the PS. If we are lucky, it will work wither way. If not, the PS will safely shut down itself, in which case swap 2 wires coming to the PS one with the other. You won't damage the PS by this, it can only refuse to go on-line if connected the wrong way.

If you have a signal cable, you can safely try to connect every wire with every other through a 50-100 Ohm resistor. But this can be a matter of another post - if you figure out that you have non-AC small signal PS control.

This test is too dangeerous, and not necessary. Instead, find which 2 of the 4 wires connect to prongs of an AC cord connected to the PS, disonnected from mains, of course, using a continuity tester. There are 4 wires total. 2 of them go from the outlet. Each of these 2 is connected to one of the prongs. 2 other are AC input of the PS.

[CODE]<--------------------------------------> <--------------|----
From AC the 4 wires to switch To PS guts
<--------------------------------------> <--------------|----.

Thats funny I though I had already said the same thing??
We discovered early on he had a 'pre-ATX' supply.
Al.

Thats funny I though I had already said the same thing?? We discovered early on he had a 'pre-ATX' supply.
Oh yes, absolutely! :) I just wanted to give another idea how to ID a PS, and -- I may be wrong, but it seemed to me that FLUTE HEAD was not completely sure as the thread went on. I did not mean to correct neither you nor anyone else, and I apologize most sincerely if it looked like I did.

Well, except maybe for that 120v-on-lugs test... :rolleyes:

:cheers:

Geesch...don't know if I should even jump in here....oh, well....anyway....most of the PCs made in this century and in the previous century's last decade have a Power Button which is a momentary switch....I won't mention service processor....but the motherboard monitors this switch....when the switch is sensed as activated...the motherboard will either power up or power down the PC. The power supply (if it's connected to AC) powers up or down when the motherboard (dis)enables it.

I'm not sure what your point is? The majority of pc's manufactured in the times you list are ATX spec. The front power switch switches the Motherboard bios and not the supply, the switch is a simple 2 wire 12v momentary. When switched 'off' by this switch the machine shuts down but the motherboard is *still powered* and will restart on a time command , wake on lan, wake on kybd or front switch.

The AT format is still used though less common. That requires an AT spec supply with a 120vac switch, not a momentary switch and switches the mains supply not the MB

The OP has an AT supply.

I'm not sure what your point is?

I agree, I'm not sure of the point either. I know for a fact there are still alot of industrial applications dated from the early 1990's that are still running with AT style boards, and around 1996, alot of MB's had both AT & ATX power supply connectors to accept both styles.
Many of these systems are powered with ISA buss specialty cards, ISA is getting rarer, so it would be very expensive to upgrade, just for a power supply.
Al.

The AT power supply switch style is a Double Pole- Single Throw, DPST. I believe fyffe555 was incorrect when he said...

"If your PC uses an on off switch at the front like the link above shows its an AT PSU and the switch is an On/Off switch - that is a two pole two throw switch. The momentary switches only work with ATX psu's.
"