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Gray wire on power supply only reads 4.6 volts

Last response: in Components
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May 30, 2011 2:44:31 AM

According to the guides on this forum, the tolerance is +/- 5%. That means my reading should be from 5.25max to 4.75min.

My question(s) will the difference between the 4.6 volts I have and the voltage I should have prevent booting.

I only have the mb, cpu and psu connected no boot, no beep. Power light on the case comes on, cpu fan and power supply fan runs.

The computer is an Acer Aspire 3400. It was working fine, powered off and the next day no boot, no beep.

The 4.6 volt reading is both connected and unconnected to the mb.

Suggestions?

Best solution

a c 144 ) Power supply
May 30, 2011 10:23:43 PM

The gray wire is not a power output. So the +/- 5% tolerance does not apply to it. It is a control signal that goes to a Logic HIGH (greater than 2.8 volts, but typically 3.5 - 4.5 volts) when the 3.3, 5, and 12 volt outputs have stabilized. The computer needs this signal to boot.

If the PSU is working properly and the gray wire is sitting at a Logic HIGH, you have the 3 main outputs present.

If you have only the CPU & HSF and the motherboard connected to the PSU and you try to boot, you should hear a series of long beeps indicating missing RAM. Silence indicates, in probable order, a bad PSU, motherboard, or CPU.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.
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May 31, 2011 3:01:57 AM

Quote:
The gray wire is not a power output. So the +/- 5% tolerance does not apply to it. It is a control signal that goes to a Logic HIGH (greater than 2.8 volts, but typically 3.5 - 4.5 volts) when the 3.3, 5, and 12 volt outputs have stabilized. The computer needs this signal to boot.

If the PSU is working properly and the gray wire is sitting at a Logic HIGH, you have the 3 main outputs present.

If you have only the CPU & HSF and the motherboard connected to the PSU and you try to boot, you should hear a series of long beeps indicating missing RAM. Silence indicates, in probable order, a bad PSU, motherboard, or CPU.


Okay, so the gray wires' output is alright. I read somewhere that this voltage was part of a check performed by the cpu. Thus my concern, thank you for clarifing the range and purpose.

Update of steps taken.

I purchased a new psu (a low cost one), and motherboard. I connected the new psu to the old board and fan runs, same as with the original.

I moved the fan, cpu and psu to the new board and fan runs, no beep, no post. This leaves the cpu as the (only?) common denominator. Assuming of course that the new stuff is operational.

Next step is to find another cpu and test again. Meanwhile I'm accumulating parts to update one of my older pcs.

Compusa here I come. Any other suggestions are welcome. I will update the results of my next steps.
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June 1, 2011 3:41:46 AM

New mb posted after adding memory. New cpu works only in the new board. The old cpu I think is deep sixed, possibly with the memory of the old board. I can't check it becuzz, somebody (wearing my face) bought a board too big to be a replacement, along with ddr2 memory sticks. Yep the original uses ddr3.

I can put the new stuff into this box (circa 2000) for a nice upgrade. Find some more cash and buy another mb, cpu, and memory. Or buy just some memory to see if the other box will then boot. Memory it is ddr3, lowest cost option. Stay turned
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August 12, 2012 11:28:37 AM

jsc said:
The gray wire is not a power output. So the +/- 5% tolerance does not apply to it. It is a control signal that goes to a Logic HIGH (greater than 2.8 volts, but typically 3.5 - 4.5 volts) when the 3.3, 5, and 12 volt outputs have stabilized. The computer needs this signal to boot.

If the PSU is working properly and the gray wire is sitting at a Logic HIGH, you have the 3 main outputs present.

If you have only the CPU & HSF and the motherboard connected to the PSU and you try to boot, you should hear a series of long beeps indicating missing RAM. Silence indicates, in probable order, a bad PSU, motherboard, or CPU.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.


The readings that I got is alright except for the grey wire which is registering 0.06V. Does this mean that my PSU is dead, if not how do I fix it to get 5V? Thanks
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a b ) Power supply
August 12, 2012 9:32:17 PM

The grey wire is a signal from the psu to the motherbd which tells the motherbd that it is now ok to boot up (all the voltages have stabilized)

If your PSU is not going to a logic high on the grey wire then you need to replace the PSU or have it repaired.
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August 13, 2012 4:58:49 AM

popatim said:
The grey wire is a signal from the psu to the motherbd which tells the motherbd that it is now ok to boot up (all the voltages have stabilized)

If your PSU is not going to a logic high on the grey wire then you need to replace the PSU or have it repaired.


Thanks for the information. I tried to test my psu connected to the board, still same reading, still no post. then I tried to directly connecting the the grey wire to a red wire which is 5V. From there I got a post... do you have any idea on what might have caused the grey wire not to go to a logic high?
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August 23, 2012 1:34:02 AM

I apologize for the way late reply. Anyway, the motherboard, cpu, and memory was fried. Parts were replaced, pc is now whirring like a champ. Still absolutely no idea what happened. Connected to a surge protector and powered down one night and the next day nopc. :ouch: 
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August 23, 2012 1:34:05 AM

Best answer selected by darebukr.
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