Hi guys,

I fairly know the ins and outs of the computer , from the time of 80386. Now I have this issue where a shuttle PC has its PSU gone bonkers.

Events:

1. Everything is turned off.
2. I switch on the AC.
3. The fans whirl and the HDD spins, for about 3 seconds and then dies. This happens without me pushing the front switch of the case.
4. Suspecting the PSU because at the side of the mobo theres this red LED which never lights up. So I isolated the front panel and turned it on by shorting the pins.
5. The thing would turn on for a second then turn off.
6. If I keep doing it, it'll just repeat the step 5. Sounds like a race car

Any ideas guys? I feel like opening this PSU up and taking a look inside. [dangerous] i know [/dangerous]

Have you tried blowing out any dust from the computer (around the fans, mainly)?Its all clean inside.is everything connected properly?do you have another pc you can try the PSU in, or another PSU you can try in that pc?Put in another PSU in place and it works.. However, that PSU won't fit in that small area.
You guys know any guide to diagnose and fix PSUs?

Thanks for helping outplease give shuttle model number for example SD39P2, SN25P, SD37P2 etc. We cannot help you if you give such little information!

In general, cure for dead PSU is to buy a new PSU. As you have Shuttle, (like me) you must get special small Shuttle PSU. But please give model number, there may be information I can give you.



I'm sending you a link to Wikipedia on power supplies:

http://en.wikipedia.org/wiki/Computer_power_supply

There are some other useful links on that page about power supplies...

To be honest...you might want to be careful if you intend to remove and repair this PSU, since they do HOLD electrical charges and this will tend to mess up your day if you're not careful. You also might want to see if you can obtain the schematics for your particular PSU...if you intend to work on it.

Otherwise...just get the manufacturer and model number of your PSU and Google it. If you can't find one...you may be able to find one comparable that fits in the existing PSU's space.Quite frankly, if repairing a PC power supply was within your capabilities, (and I am NOT being sarcastic or putting you down) you would not be asking on here. You would have your soldering iron and your digital voltmeter out and be doing it.

For those people who are not already a skilled electronic technician with good diagnosis and repair skills, the standard method of dealing with a failed PSU is replacement.

You need to be able to diagnose and repair a complex piece of electronic equipment, namely a switch-mode power supply.

If you can understand the following and relate it to what you need to do, and understand the danger of electric SHOCK, perhaps you could go ahead. Otherwise in your place I would be contacting Shuttle.

Also called switching power supplies and sometimes chopper controlled power supplies, SMPSs use high frequency (relative to 50/60 Hz) switching devices such as Bipolar Junction TRANSISTORS (BJTs), MOSFETs, Insulated Gate Bipolar Transistors (IGBTs), or Thyristors (SCRs or triacs) to take directly rectified line voltage and convert it to a pulsed waveform.

Most small SMPSs use BJTs or MOSFETs. IGBTs may be found in large systems and SCRs or triacs are used where their advantages (latching in the on state and high power capability) outweigh the increased complexity of the circuitry to assure that they turn off properly (since except for special Gate Turn Off (GTO) thyristors, the gate input is pretty much ignored once the device is triggered and the current must go to zero to reset it to the off state.)

The input to the switches is usually either 150-160 VDC after rectification of 115 VAC, or 300-320 VDC after doubling of 115 VAC or rectification of 220-240 VAC. Up to this point, there is no line isolation as there is no line connected (large, bulky, heavy) power transformer.

A relatively small high frequency transformer converts the pulsed waveform into one or more output voltages which are then rectified and filtered using electrolytic capacitors and small inductors in a 'pi' configuration C-L-C, or for outputs that are less critical, just a capacitor.

This high frequency transformer PROVIDES the isolation barrier and the conversion to generate the multiple voltages often provided by a SMPS.

Feedback is accomplished across the isolation barrier by either a small pulse transformer or opto-isolator. The feedback controls the pulse width or pulse frequency of the switching devices to maintain the output constant. Since the feedback is usually only from the "primary" output, regulation of the other outputs, if any, is usually worse than for the primary output. Also, because of the nature of the switching designs, the regulation even of the primary output is usually not nearly as good both statically and dynamically as a decent linear supply.

Some repair tips here

http://www.smps.us/computer-power-supply.html

If you have not got a good digital voltmeter, a decent temperature controlled soldering iron, a dummy load, etc, you will have to buy or make these things, and you might as well put that money towards a new PSU.

Anyway, that's just my opinion.
thanks contrex for the detailed reply. Yep, i'll take it up as a challenge. Fortunately, currently doing electrical and computer sys eng