VStanby (V SB) question ?

[bianchi77]

Guys,

If V Standby (V SB) on ATX PSU is less than 5V,
Is it the cause of Power Supply can not be turned on ?

I see the diode on 5V SB is 0.1V on Vf diode test on DMM diode test...even I reverse the polarity....suppose to be OL on reverse and about 0.3V-0.7V normally..
Any clues ?

[stj]

Re: VStanby (V SB) question ?

what voltage are you seeing?

[bianchi77]

Re: VStanby (V SB) question ?

2.5v can it be a bad coupler? I replace diode and now it's 5v I can hear high pitch tone when it turns on. The cause is a short FET on motherboard...do u reckon? Can it be the secondary rectifying diode is faulty?

[stj]

Re: VStanby (V SB) question ?

could be the capacitors on the standby output - they fail a hell of a lot because they run 24/7 and there is no cooling in standby because the fan stops.

[bianchi77]

Re: VStanby (V SB) question ?

ok I'll have a look on it...if this caps fail...everything shuts down ?

[bianchi77]

Re: VStanby (V SB) question ?

I've found 2 bulge capacitors 2200uF/16V on the secondary side...could be this one is the major problem ?
I haven't checked which one is connected to 12V / 5V...
I'll replace it and see...

[bianchi77]

Re: VStanby (V SB) question ?

I've replaced them, no avail, can it be the rectifying diodes ? it's SBL1040 and when I measured it on diode test I got 0.1V...and there's one FET on 3.3V rail...
any ideas or schematic for it ? or it's faulty SG6105 PWM buck controller ?
I've tested the opto as well, all good...25 ohm when LED is on..

[bianchi77]

Re: VStanby (V SB) question ?

Photo of the PCB, I 've taken out the secondary rectifier...
PCB serial code :
LEC-011
REV:1.2

Any ideas for the schematic ?

[bianchi77]

Re: VStanby (V SB) question ?

The case :
Ritmo LPF2SS

[Khron]

Re: VStanby (V SB) question ?

Those two black caps near the top of the board, near the small transformer - are they Fuhjyyu? Either way, if the 5VSB is low, those would be my first suspects.

[bianchi77]

Re: VStanby (V SB) question ?

are you talking about these caps ?

[bianchi77]

Re: VStanby (V SB) question ?

Let me take close up picture so you can see what exactly it is...

[bianchi77]

Re: VStanby (V SB) question ?

Capacitor photos

[budm]

Re: VStanby (V SB) question ?

You have already found two bad caps with bulging top, you might as well replace the whole set of the caps since bad caps may not show any sign of bulging on top, otherwise you need to check the Capacitance and the ESR of the caps.

[bianchi77]

Re: VStanby (V SB) question ?

does it mean that I should desolder all the electrolityc caps and check, or just replace 'em ?

[bianchi77]

Re: VStanby (V SB) question ?

Will a bad caps make the PSU completely shut off ? from I can see there's no problem with the diodes, I have check one by one....

[budm]

Re: VStanby (V SB) question ?

Will a bad caps make the PSU completely shut off ? from I can see there's no problem with the diodes, I have check one by one....

Bad cap will cause the power supply not to run properly: I.E. will not run, low Voltage, cycling on and off, etc.

[budm]

Re: VStanby (V SB) question ?

does it mean that I should desolder all the electrolityc caps and check, or just replace 'em ?

You already have bad brands of caps being used so just replace them with the good and correct type of caps, it wastes a lots time unless you want to buy the test equipment and analyze each caps OFF the board.

[bianchi77]

Re: VStanby (V SB) question ?

ok, so do you reckon there's no problem with SG6105 PWM chip ?
This PSU is completely off, was on before, but suddenly off...
and I got only V Sb 5V on.....

[budm]

Re: VStanby (V SB) question ?

ok, so do you reckon there's no problem with SG6105 PWM chip ?
This PSU is completely off, was on before, but suddenly off...
and I got only V Sb 5V on.....

Was on before what? Before you are working on it?
You indicated the 5VSTBY is less than 5V and the power supply cannot be turned ON, so how did you get it to turn on then?
Also now you indicate "This PSU is completely off," So now you have nothing period, no STBY, none?
Very confusing.