SMPS shows output voltages within range, yet doesn't boot the system.

[helion]

As the title says, the PSU doesn't boot the system. It only does after CMOS is cleared each time. I tried with a different PSU it worked okay.


The PSU had apparent leakage from the base of a pair of caps. I replaced them with new ones, yet the same issue persists. It shows voltages on the 12 volts at 11.5 v etc. All of the voltages are alright as per the link below.

http://pinouts.ru/Power/atxpower_pinout.shtml

What might be the cause I wonder.

As to the 'leakage', there are no physical issues with the caps, like bulge or the rubber coming out at the base - only the brown vinyl glue like residue at their base which was not there at the same caps in the PSU which worked to boot normally.

What tests might I carry out on the PSU to identify the cause?

The PSU is an ATX 250Watt PSU.

[Hemingray]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Caps do not have to be bulged/physically leaking to be bad. What brand are they?

[debjit625]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

The PSU is an ATX 250Watt PSU.

250 Watts is not enough for modern PC board,atleast 300 to 450 Watts needed.You can also remove any non necessary peripheral like add on video card to reduce the power consumption for test purpose.

To test the PSU you can use a load resistor (keep in mind about the wattage).Suppose your PSU says it can source 12Volt at 1Amp use a 12 ohms 12 watt resistor to check,normally 12 ohm resistor will be not available ,so you can use a near range like 15 ohms 10 watts resistor.

Good Luck

[PCBONEZ]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

250 Watts is not enough for modern PC board

No necessarily true.
Many modern systems use very little power.
.
250 watts is usually enough for modern systems that use an average CPU, 1 HDD, 1 optical, and a modest [or onboard] video card.
.
Many come that way from the factory.
For example most Dell clam-shell systems using C2D come factory with a 210 watt.
Most of the Atom based systems don't need much either.
.
The trick is to have the amps on the correct rails.
[Meaning use a PSU spec'ed for the system type.]
An old style 250 watt will be heavy on +5v and be light on +12v.
Most modern boards need more amps on +12v.
.
Now, if you are going to spin a bunch of drives or have some power guzzling CPU or a watt hog video card then 250 watts isn't going to cut it.
.

[PCBONEZ]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

As the title says, the PSU doesn't boot the system. It only does after CMOS is cleared each time. I tried with a different PSU it worked okay.


The PSU had apparent leakage from the base of a pair of caps. I replaced them with new ones, yet the same issue persists. It shows voltages on the 12 volts at 11.5 v etc. All of the voltages are alright as per the link below.

http://pinouts.ru/Power/atxpower_pinout.shtml

What might be the cause I wonder.

As to the 'leakage', there are no physical issues with the caps, like bulge or the rubber coming out at the base - only the brown vinyl glue like residue at their base which was not there at the same caps in the PSU which worked to boot normally.

What tests might I carry out on the PSU to identify the cause?

The PSU is an ATX 250Watt PSU.

The PSU gurus will need more detailed info on the PSU and symptoms before they can help.
- Photos are good too. [Upload them through 'advanced' screen, don't link.]

The brown glue is know to become conductive when it gets old.
.

[Th3_uN1Qu3]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Pictures of the power supply guts please. It could be a POWER_OK signal that takes too long to come on or a weak 5vsb rail.

[helion]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Pictures from my camera Intel CS630 did not show anything clearly enough, so I dropped the idea of taking pics and posting.

It is a DEER PCB with DR-200ATX v2.02 printed on it. It was sold as the brand Zebronics here in India. Some browning of the board is there at one of the resistors R66. The caps I removed are of a brand called Viva, and the ones I put in as replacements are Teapo.

I've used it on a Pentium3 System with only the D815EEA Board, Processor, RAM and the HDD.

Replacing the PSU is cheap enough but I see that repairing it will be a good exercise too .

[japlytic]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Deer is a known bad brand of power supply, of which was sold under various brand names.

[helion]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Update:

I have been rechecking the voltages on the PSU, and I now find that the 12v rail shows 11.07v to 11.13v. The time I first checked and posted this thread, it showed 11.46v to 11.48v.

I seem to have 'found the cause' why the PSU did not boot up - the 12v rail. The 5v standby and POWER_OK show unchanging values, at 5.04v. The 3.3 volt rail shows 3.36v and the 5v rail shows 5.24

I am beginning to wonder if this can be corrected properly, so that it performs like the other working PSU which consistently shows 11.98 there abouts.

[Th3_uN1Qu3]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Replace the capacitors on the 12v line. But if it has the "diodes-on-a-bracket" thing for 12v, with two diodes in DO-201 package like FR302s or thereabouts soldered to a bracket that is screwed into the heatsink, forget about it.

[kaboom]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Don't forget to add:

Missing X/Y caps
Common-mode filter chokes
NTC thermistor
"Properly-rated" fuse
All small caps

Either keep the original heatsinks and use grossly overrated semis, or make/find better ones. In any case, pull any TO-220s out and use TO-247s.

Oh Deer, how else can we improve it? How about some real wires, not that 22awg aluminum- with all the ampacity of 24awg copper.

Way to

[helion]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Replace the capacitors on the 12v line. But if it has the "diodes-on-a-bracket" thing for 12v, with two diodes in DO-201 package like FR302s or thereabouts soldered to a bracket that is screwed into the heatsink, forget about it.

Well, that is the case.

I'm going to now replace the PSU itself following your suggestion of giving up attempts at this one. However, I would want to know why it leaves no other options. Is it the economics, or is it that any further investigation would be too tedious/complicated/uncertain?

[Th3_uN1Qu3]

Re: SMPS shows output voltages within range, yet doesn't boot the system.

Purely economic. The circuit is very simple, but it would take a lot of work to make it do something useful. The only situation where it is worth bothering is if you're going to do major mods and use it to power something else than a computer.