Faulty Power Button on Dell Optiplex GX755 Desktop PC

[#1]

I have two of these GX755 Desktop PCs. The one I normally use has failed - the power button made a 'crack' sound when I tried to turn it on, and the button is now permanently a couple of mm further in to the box than the one on the other GX755. I have opened up the box to see if I could remove the switch to somehow change it, but there is the heat exchanger on the uP to remove first of all, and then a fan. Who knows what follows that.

If anyone in the forum has experience of changing the power button, please would you identify for me where the cable from this button goes to, and how the button/cable assembly works? Is the assembly just two wires that the button shorts together? I understand it just replicates the paper clip test (shorting green to black) when testing the output of a PC psu.

If I cannot remove the button, and fit a new one, then what I am thinking of doing is disconnecting the power button cable from wherever the other end is, and bringing a sort of replacement cable out of the PC box to a press-to-make button.

Thanks for any help

[#2]

Usually the wires from the switch go onto the motherboard connectors. Position varies between makes. Generic type thing really. Your biggest problem will probably be fixing it to the case, so getting a like for like replacement is key. If you can get the switch out, it'll have a number. Ebay or if you're feeling a tad richer, RS or Farnell will probably have a clone. As you say, it just shorts out 2 wires (normally).

[#3]

Thanks idonno.

I have looked at a diagram of the motherboard for the Desktop variant of the GX755, and there is no obvious connector for the Power Button to connect to. Neither is there a cable connecting to the motherboard or the psu that just disappears into the works. The only thing I can think of is that perhaps the Power Button cable goes to another sub-assembly such as the Front Panel pcb which is tucked in between the fan I mentioned and the metalwork for the hard drive/DVD drive assembly. However, I cannot see a mystery cable coming to that either.

[#4]

I had a similar problem with my Dell inspiron Laptop.... found an excellent "tutorial" on You tube... got the replacement from Ebay... set up the second laptop with the TUT showing on screen... and proceeded "page by page" so to speak ... it was a "doddle"    it would have been a nightmare without it, as I had no idea how to "lift" the keyboard from the main chassis...

so... I did a google of your title,.... ( and it shows your query as number 1 ! ! )

https://www.google.co.uk/search?source=hp&ei=ZwA4XavSIO-ugwepzoe4Cw&q=+Faulty+Power+Button+on+Dell+O...

however, it seems there is a couple of videos on you tube that may well be what you need...

Good Luck

[#5]

Hello Shutter,

I have just watched the video you discovered. I think taking my pc apart would be a lot simpler than that (famous last words). I am just a bit concerned about the heatsink that I have to remove first, because of the need to renew the thermal paste when I reassemble it. There must be somewhere I can get that (ebay?).

However, googling for a replacement switch has revealed two possibilities, both of which conform to my suggestion that maybe the cable from the button goes to the Front Panel pcb. The problem is, the cheapest of these is over £20, so I think I will strip the PC first to see what switch I need. It's a possibility that it is the plastic button on the Power Button Assembly that has broken, so maybe I just need to get that out of the way. I will find out when I've investigated. Will let you know

Cheers

[#6]

An update! I have taken the heatsink and the fan out to get to the Power Button, only to find a metal grid in the way. The grid couldn't be removed, so I had to remove the front plastic cover. The fan was covering one of the front cover attachment clips, so it wasn't a waste of time removing it. Having done that, I found the cause of my problem. You know the round DELL badge - it had attached to the back of it, an arm which acts as a spring on the power button. The end had broken off this arm, and there was nothing wrong with the power button itself.

Incidentally, the power button doesn't have a cable. It has another arm which operates a pressure switch on the Front Panel circuit board. So now I am looking for a scrap Dell pc which might have that first arm.

And now for the bad part. I found that when I took the fan out, I had caught and broken two electrolytic capacitors on the motherboard. They only have the following written on them:-

87H

561

04V

Not what I am used to on capacitors. I don't know how much of that is the capacitor description, nor if they should be combined. They are all that is written on the capacitor. I have tried Googling them, but have had no luck so far, so I may need a Dell motherboard as well.

Onwards and upwards

[#7]

There`s lot of information on this google search fro   Dell optiplex GX755 motherboard circuit diagram

https://www.google.co.uk/search?source=hp&ei=5HA4XeCBK4KTlwTviaToDw&q=dell+optiplex+GX755+motherboar...

there are some videos, and someone has replaced "Faulty" elec caps... maybe there is some info hidden somewhere amongst this lot,.. to give you the "alternative" replacement I.D`s

Regarding the heat sinck paste... yes I think I have seen it for sale on Ebay..

Another way to find info would be to use the title in an "IMAGES" search... and see what comes up from that...

[#8]

Yes I've seen that video. I've repaired things before where electrolytic capacitors have started to bulge. These videos always show the same type of capacitor. They have the capacity value and voltage clearly written on them, so identifying the correct replacement is easy. My problem is that what is written on the capacitors I have damaged doesn't identify those values, not even by the standard id used on vertical chip capacitors (I think that is the correct name). These look like surface mount devices but without the square base-plate. Googling doesn't seem to identify them either, but then I did include all 3 codes.

By the way, the two arms I mentioned to do with the power button - I was wrong. They are one piece, the arm from the Dell Badge had broken from the button, so the whole thing is mounted at the Badge end only. There is a bloke in France advertising one for over £30 (if he still has it - I don't know how old the ad is).

Cheers

[#9]

OK.. so the button is broked... can you repair it with a patch of other plastic over the back, and all araldited together.. ?  

Or... sus out the actual switch it operates, and "fix" it so it is in the ON position permanently, and then all you do is switch it on from the wall socket.

[#10]

That will be my final cure. In the meantime, I am putting feelers out to people who are still working to see if they have any scrap Dell pcs that might supply the parts I need. I still haven't identified the capacitors I damaged, though they seem to be Aluminium-Polystyrene(that might not be quite correct) capacitors, judging by what I have found by Googling.

[#11]

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@penneck wrote: I have looked at a diagram of the motherboard for the Desktop variant of the GX755, and there is no obvious connector for the Power Button to connect to.

Presumably this manual ...maybe  Have a look at pages 5 / 6 depending of course if it even covers yours!!!! The connector is the front panel connector. e.g. Number 8 page 5. etc.

Your later post of blown capacitors don't sound good. Sometimes its easier to just bin the motherboard (depends on form factor) and get a new box! Been there many years ago. I have been known to put a new very cheap motherboard, cpu and memory to an old box.

If you do manage to get the capacitors replaced but have no luck with a power button, there is, according to the blurb of words, the option for auto power 'ON'. in the bios. Might be the easy way to go. Just switch on at the socket and it'll boot (power button or no power button.).

Have fun!

Edit - usually the power switch is a spring loaded contact i.e. momentary contact. It isn't an 'always on' contact. If you do short it out permanently, you might end up with the computer refusing to boot i.e. 'registering a fault'.

[#12]

In the last couple of days, my knowledge of the power button and the capacitors has gone from zero to a bit, with many changes on the way.

The power button is a weird shape which attaches to the body behind the Dell badge, and stretches across to the Front Panel Assembly where it operates a push-button, push to make switch. The power button has snapped just as it gets to the button you push. As you indicate, I cannot just lock the switch on the Assy in the On position, so I may have to remove this switch, then attach another switch which is external to the PC box - they tend to be too big to fit where the push button goes because they would stick into the fan.

As for the capacitors, I am having to assume the 561 on the old capacitors means 560uF, so I am searching for 560uF capacitors that have a body 8mm high and 8mm dia. I have had some success, but it has a working voltage of 6.3V. When I get desperate, I may try these.

[#13]

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@penneck wrote:

then attach another switch which is external to the PC box -

Just drill a hole into the side / front of the case near the existing switch if possible. You might be able to directly connect the switch to the existing wires.

Depending on where it is on the motherboard 6.5v might be fine (3.3v & 5v rail). Just make sure you have a steady hand while you solder! Nothing worse than solder everywhere. I find one of these comes in handy as well.

[#14]

A solder sucker - at least that was what we called them. Have used them many a time over the years. The nozzle on mine is looking a little worn

[#15]

To bring this up to date:-

Rather than replace the damaged capacitors on my motherboard (I couldn't identify them reliably), I bought a used motherboard, the correct one for my version of the 755. I moved the uP from my board to the replacement, and fitted it in the box.

The problem of the snapped power button I have tried solving by fitting an electrical switch in the floppy drive blanking plate, and wiring it in parallel with the electrical switch the power button was supposed to operate. I didn't take the old electrical switch out. The original electrical switch seemed to be a push-to-make, momentary switch, so my new switch is similar.

The pc now powers up and goes through the normal Dell screen view, but instead of going on to the Windows Bootup screen, it complains that the battery voltage is low (press F1 to continue, press F2 to run setup, etc). I have tried them all, but when I press F1, it goes to the Win XP screen (yes I'm still using it) but after just 2 or 3 seconds, it reboots back to the Dell screen and goes through to the message about the battery.

When I tried F5, it went through the diagnostics without a problem.

So, do I just keep the pc on until the battery recharges? Have I done something wrong when I repaired the pc? Any suggestions, please?

Thanks