12V rail is not on ?

[budm]

Re: 12V rail is not on ?

https://www.badcaps.net/forum/showth...t=55771&page=2
Are the two jointed legs of the sub diodes touching the heatsink? How are all 3 legs connected to the board?
NEVER MIND, you changed them to something else.

[budm]

Re: 12V rail is not on ?

https://www.badcaps.net/forum/attach...4&d=1469140301
Look at the diagram, you have load resistors in the circuit, all you have to do is looking at how the current will flow when you hook up your 9V, 1K, and LED to the Diode you are testing then you will understand why the TEST LED will light up in both directions.

[budm]

Re: 12V rail is not on ?

I test D22,D20,D17,D18 in circuit with 9V and LED,1K ohm....something is not normal...
It's on a both side of test reverse and forward bias...
Are they all bad ?
or to be sure must be off circuit ?
PCB code Y-B200 ATX Ver 2.6...and they are on 12V and 5V rail...

Test them OFF the board!

[bianchi77]

Re: 12V rail is not on ?

I test D22,D20,D17,D18 in circuit with 9V and LED,1K ohm....something is not normal...
It's on a both side of test reverse and forward bias...
Are they all bad ?
or to be sure must be off circuit ?
PCB code Y-B200 ATX Ver 2.6...and they are on 12V and 5V rail...

[bianchi77]

Re: 12V rail is not on ?

Not shorted...and the diode for 12V rectifier is only 0.4V so I need to replace it as well....
waiting for replacement, I want to replace them all with SBL3040..

[CapLeaker]

Re: 12V rail is not on ?

I can't check the voltage because I unsoldered the rectifier for them...
I suspect 2 SBL1040 are bad....0.1V only on diode test...

Change those. The SBL1040 should have a voltage drop of 0.6 on your diode test. Does it show shorted too when you reverse the leads?

[bianchi77]

Re: 12V rail is not on ?

I can't check the voltage because I unsoldered the rectifier for them...
I suspect 2 SBL1040 are bad....0.1V only on diode test...

[CapLeaker]

Re: 12V rail is not on ?

Why do you think the PWM is bad? you got any voltage on the secondary's besides STBY power, when you jump STBY to PSon?

[bianchi77]

Re: 12V rail is not on ?

Do you know where we can find that chip ?
I tried googling it and can not find...
or the similar chip with that one ?

[CapLeaker]

Re: 12V rail is not on ?

Had the wrong schematic up. U3 is the PWM. Look at "PWM of the year"

https://www.badcaps.net/forum/showthread.php?t=35007

[bianchi77]

Re: 12V rail is not on ?

U3
2003

down on the bottom of the schematic, connected to PS_ON

[CapLeaker]

Re: 12V rail is not on ?

D7 should be the same as D9. I don't see any U3. The IC's you cant test most of the time. They either work or don't. An oscilloscope comes in handy with that.

[bianchi77]

Re: 12V rail is not on ?

is U3 = ULN2003, darlington array ?

[bianchi77]

Re: 12V rail is not on ?

and D7 is weak only 0.2V

[bianchi77]

Re: 12V rail is not on ?

I have checked all the transistors and diodes, they are in a good condition...
so only these three diodes are under the normal condition...
how do you reckon guys...?
No problem with the capacitor as well ?
How about the chip ? U1,U2,U3 ?

[bianchi77]

Re: 12V rail is not on ?

Ok...so most likely SB1040 because I tested on diode mode only 0.1V...too low...
I'll change three of 'em anyway to SB3040....

Meanwhile I'll check other transistor..

I'll keep posted..

[CapLeaker]

Re: 12V rail is not on ?

I can see 2N60 on the PCB, I unsoldered it, but can't find it in the schematic ??

It's in the schematic. Q3. That wouldn't be it anyway, because it isn't blowing fuses.

[bianchi77]

Re: 12V rail is not on ?

I can see 2N60 on the PCB, I unsoldered it, but can't find it in the schematic ??

[bianchi77]

Re: 12V rail is not on ?

My DMM is autorange

[bianchi77]

Re: 12V rail is not on ?

The resistance I measured 6M5 and open line...