Is my PSU beginning to fail?

[Kick]

Hi,

 

I have an elderly refurbished HP DC7900 SFF desktop that has given me excellent service. Lately, however, I have experienced a few minor irregularities when I power up the computer. Sometimes I need to have a second go at operating the power switch or sometimes there seems to be a lag before the power kicks in. Afterwards the computer boots with no problems and runs normally throughout the work session. I recently changed the power switch assembly to see if that made any difference and coincidently, things were better for a while but the situation has returned.

 

Being not very experienced in such matters, I would welcome any comments and advice from any of you technical wizards that have always been so ready to help the likes of me on this forum.#

 

Thanks.

[Tony D]

I recently changed the power switch assembly to see if that made any difference and coincidently, things were better for a while but the situation has returned.

Wonder why it seemed to fix the problem, yet then the problem came back.

 

Could very well be the power supply. Would be nice if you had one to swap out. If you have a volt meter and know how to use it, you could run a test to see if the signal to start the computer is being sent to the power supply.

[Kick]

Hi Tony,

 

Thanks for your reply. The problem has been erratic so the temporary improvement, after I fitted the replacement switch assembly, may have just been coincidental. I opened the computer today to check the power supply unit specifications and as access was now possible, I checked the easiest to get at connections by easing and then pushing them fully home. Again this may be coincidental but on three separate startups afterwards, there has been no problem so I'm hoping all is well.

 

I do have a multi-meter which I can set for AC (200v and 500v) and DC (200mv to 1000v) readings which I am capable of using for routine electrical and electronic testing although I'm not sure exactly what or how to test with the PSU. The 230/240v AC mains seems to get through to the power supply OK as far as I can tell though it might be worth checking plug terminals in case a connection has loosened - it's probably wise to check the simplest things first.

 

I'll update you when there's something to report.

 

Cheers.

[Tony D]

Here's some info that may help. The problem you have is that you're dealing with an intermittent problem. You'd have to attach test leads to the power supply connector and have them available externally for measurement when the unit fails to turn on.

 

Here's a little tutorial on checking power supplies.

Use a Multimeter to Test Your Power Supply

Note: They short out the PS-ON pin to ground. I don't want to do that in this case. That forces the power supply to turn on. (I don't like the fact that they're using a paper clip without a series resistor.) We want to see if the main board is telling the power supply to turn on.

 

Here's some basics.

1) The power supply (PSU) supplies a constant stand-by voltage (+5V) to the main board. That's pin +5SB.

2) The PS-ON pin is typically around 5V with the power supply connected. That would be pin 16 on a 24-pin connector; pin 14 on a 20-pin connector. When you press the power button on your computer, the system board pulls that voltage down to around 0.5 V. I'd like to check that pin to make sure that pin is initially around +5 V and that the main board is pulling that voltage low telling the PSU to turn on.

 

Note: It's preferable to use a resistor in series with the test lead. Maybe something like a 1 K Ohm.

 

Determine if you have a 20 or 24-pin connector.

 

This is a pin-out of a 20-pin connector

 

 

Here's a pin out for a 24-pin connector.

 

[Kick]

Hi Tony,

 

You've gone to a great deal of trouble so many thanks.

 

I've considered other possibilities that might cause similar problems at startup. I thought the HDD might be the culprit as, when I switch on and experience the problem, the HDD LED is not lighting up or is slow to light up but then that could because the PSU is not providing the power. However, once I've got the computer started up and run the HDD Tune software to test the HDD, no problems are found and the temperature is in the mid 20s C. Replacing the HDD, if that were the problem, wouldn't be an issue for me as I have my partition image backups on an external drive and I have thought about getting a bigger capacity drive in the past. Another possibility is the motherboard but if that is the problem then it is not a financially viable option to replace it on my elderly computer. Replacing the power supply with a new one is not financially viable either - they are hard to find in the UK and cost more than the computer is worth (it would be better to get a replacement refurbished computer). Refurbished/pre-owned PSUs are available on EBay at UK prices of about the equivalent of 40$ so that might be worth considering if tests confirm that the PSU is failing.

 

When I feel brave enough I might get around to running the tests that you have described for me but I am getting rather shaky in my old age and find doing more delicate work rather tricky. For example, I would not attempt any soldering on a circuit board nowadays.

 

Well I've plenty to think about - you've done me really proud with your advice. I've bookmarked the link you provided and copied the images and related text. I'll get back to you when I have some news.

 

Cheers and best regards, Kick.

Edited April 25, 2018 by Kick

[Kick]

Hi Tony,

 

Re: my message sent to you at computerhelpforums.com/conversations/.

 

I'm not holding my breath regarding the improvement in the PSU after blowing out fluff as I had a minor hiccup starting the system 20 minutes ago. It may have been my fault possibly holding the switch in too long - the second attempt worked after a very short delay. Possibly there is more fluff to remove but as I did not open up the PSU case, perhaps a more thorough clean is required. I am not sure the startup problem was due to over-heating because the worst problems were after the computer had been off a long time - perhaps it was due to temporary shorting. Whatever the cause, I am now sure it is to do with the PSU so if the fluff cleaning does not completely resolve the issue I will not replace the unit - I've been advised a refurbished or second user unit may be risky and a new one (and they are few and far between) is to expensive in relation to the value of the the PC. I'll keep you updated on the PSU - obviously as the fluff cleaning had such a noticeably positive impact, it is not yet a lost cause. I'll see if I can open up the case for a more thorough clean.

 

My problem trying to get on to this forum earlier was that my bookmark still had the old address. Recently I have been accessing the forum through my Last Pass password organiser which I had updated, today used the out-of-date bookmark (that's now resolved).

 

Regards, Kick.

[Tony D]

Another thought is to reseat the RAM. If there are more than one RAM module, try running without one for a while. Bad RAM can also cause this type of intermittent problem.

My problem trying to get on to this forum earlier was that my bookmark still had the old address.

That was a problem. I also had to update my bookmark.

[plodr]

I had to re-do my shortcut to get here. Now to do the other computers.

[Kick]

Hi Tony,

 

I found the RAM was ok. I'm beginning to think the problem may well be a dry joint on one of the components on the circuit board within the PSU. When the computer has been on a while and then powered down, it often starts up normally if switched again within say an hour.

 

First startup of the day is usually the worst but there does seem to be a pattern emerging to the bad starts as follows: the first press of the power switch puts the HDD LED on and the drive begins to run until I release the switch (during this stage the power LED remains off; the next press of the power switch more or less repeats the first press; the third press of the power switch does nothing ( no LEDs glow) and the fourth press, if I hold it in, causes the power LED to glow faintly - on release of the switch the power LED remains glowing faintly at first but gradually brightens - when it reaches normal brightness there are a couple of faint clicks suggestive of a relay switching and the HDD LED comes on brightly and the drive runs.

 

I have now invested in a new desktop computer which I bought without an operating system. I purchased an OEM version of Windows 7 SP1 Pro at a reasonable price from a reliable source (it was genuine). However, after 4 days of setting up, transferring files and installing software, out of the blue, the dreaded Microsoft warning message stating my operating system product ID was invalid. A frantic call to the Microsoft validation telephone number proved useless as there was so much distortion and break up on the line I couldn't make sense of anything. With further research on-line I found another Microsoft telephone number and was put in contact with a real person in a Microsoft call centre in Mumbai. This line was not that clear with much background noise but, with a little difficulty, I was able to communicate with a very helpful advisor. He was able to confirm that the product ID was valid and set my system accordingly. I was prepared for a plan 'B' with a live DVD of the latest LTS version of Linux Mint but for the time being I have Windows 7 running very well and all updated. I do not intend going the Windows 10 route.

 

I will continue with the desktop with the PSU problem until it packs up for good and then salvage any useful bits.

 

Cheers, Kick.

[Tony D]

Thanks for the update. PSU can be purchased for under $40. ... just a thought

[Kick]

Hi Tony,

 

The computer is a small form factor model and requires a specific power supply unit that is no longer manufactured. There are a few new PSUs of this type still available but they tend to be priced at somewhat over 100$ in your money. Even refurbished or second user units can be fairly pricey and, of course, may be unreliable. The computer isn't worth spending the cash on so I will keep running it as it is until it packs up completely. Afterwards I will retain the HDD and DVD-RW units and scrap the rest.

 

I'm pleased with my replacement which is much quicker - the only minor issue with it is the DVD-RW eject button on the front panel which, owing to poor design of the linkage between the panel button and the actual eject button on the DVD-RW unit itself, is unreliable. However there are work-arounds and I can do all I need to do - when the system is running, I can right click the drive icon and select 'Eject' and when the system is off, I can open the drive flap on the front panel which, although it doesn't expose the button on the drive, does allow access to the little hole below the tray and probing with a straightened paper clip through the hole releases the tray - if I need to boot from an emergency live dvd or cd then I can load the disc this way.

 

I suppose this thread is now exhausted and we can call it resolved even if the problem itself is not cured. I've enjoyed the conversation and thank you for your advice and suggestions - I've learned a fair bit too from my expert tutor.

 

Cheers and regards, Kick.

[Tony D]

and that's why I don't recommend small form factor computers. You can't go to your local computer shop and get an inexpensive power supply.

[Kick]

Hi Tony,

 

I take your point about small form factor units. I bought the computer at a very reasonable price as a refurbished ex business unit and it has served me well for several years so I can't complain - it's been good value for me. My replacement desktop is a tower unit with a standard sized psu - there's tons of space inside the case and it has very good ventilation - I can see clearly through the grilles to keep an eye on dust and fluff build up and the side panels are simple to remove when the time comes to clean.

 

Cheers Kick