mercury pc power supply only 5vsb supply.

[playit]

hello fellow members,i wanted to test my old psu for my case fans ,so i opened it and checked with psu tester and multimeter and some cold testing ,hot testing with some help of videos,but couldnt go much further and am confused,please help me. psu has only 5vsb output ,green wire and purple wire gives 5 v.

[playit]

Re: mercury pc power supply only 5vsb supply.

on hot testing the green thermister doesnt show any voltage, please tell me what i should test in input section and output section in cold testing, i will post results asap.thank you ,hope i would succeed in my first electrical project ..smiles .

[playit]

Re: mercury pc power supply only 5vsb supply.

anyone pls ??

[R_J]

Re: mercury pc power supply only 5vsb supply.

The green NTC thermistor looks cracked, and is likely close to being open, but it is not likely the only problem because if it was open. you would not have any +5v standby. post what the numbers printed on it, or post a picture of it. (might be SCK 2R58)
It is possible that when the main section of the power supply starts up the NTC does open and the power supply turns off.

You can check the DC voltage ACROSS the two large capacitors in the primary, be carefull this is the HOT side of the power supply, You should read about 160vdc across the caps.
If you have this voltage, check that large resistor at the end of the heatsink (next to the board number) if it is ok, I would replace both the small electrolytcs between D2 and that small transformer, they are likely bad (due to heat)

[PeteS in CA]

Re: mercury pc power supply only 5vsb supply.

The green wire is PS-ON, an input from the motherboard. Typically that signal has to be low to enable the main inverter and output voltages. If I understand your post correctly, you measured ~5V on the green wire, so grounding it might turn on the main outputs.

[playit]

Re: mercury pc power supply only 5vsb supply.

green thermister is sck 053, 2 large primary capacitors showed hot test voltages shows 145 and 144 volts somthing.. ,the resistors show right ohms... any way to check the 2 small capacitors you told me or diodes there? thanks so much for the replies..

[playit]

Re: mercury pc power supply only 5vsb supply.

i did hot test to see vcc supply ,the power ic chip is wt7520 815 j22ab ,so i got data sheet for wt7520 ,the vcc supply is 5.5 v , but i got .5v from one big filter capacitor and .5v in other filter capacitor ,so its bad i guess ,have to check from input area as per some internet chip,hope this might be of some help in guiding me,thanks again

[R_J]

Re: mercury pc power supply only 5vsb supply.

The ic's vcc likely comes from the 5 volt standby supply, follow the vcc line, there may be a small resistor open. There seems to be two diodes coming from the standby transformer, one will be the +5v standby you measured earlier, the other one is likely for the ic's vcc
See if this helps, photo from danyk.cz

[playit]

Re: mercury pc power supply only 5vsb supply.

hi rj, could you please point out in my pic at back side, i am not good at circuits,i tried ,but it looks different in my smp,confused.. sorry i have to learn so much, smiles

[R_J]

Re: mercury pc power supply only 5vsb supply.

This is not an exact schematic, it is just one that uses the same ic, Your picture is not clear enough to follow the traces in that area.

[playit]

Re: mercury pc power supply only 5vsb supply.

is this pic ok?

[R_J]

Re: mercury pc power supply only 5vsb supply.

Can YOU trace pin 13 of the ic based on this picture? You have the board, pin 13 needs +5 volts but has 0 volts, This is the best I can do, there seems to be a coil (marked in green) Chck that you have +5v on the two caps I marked.
There seems to be a jumper wire (J0) next to the GP marking, It looks a bit corroded, check it.

[playit]

Re: mercury pc power supply only 5vsb supply.

i kept black probe of multimeter in black wire of outlet psu wire ,shorted green black wires, at vcc pin 13 i got 5 v,both capacitors positive points got 5v with red probe.

[R_J]

Re: mercury pc power supply only 5vsb supply.

So you do have +5v vcc on the ic. not 0.5v like in post #7
Check the voltage on the drive transformer (check voltage here). If there is no voltage there, check on boths sides of R23, I suspect it might be open.

[playit]

Re: mercury pc power supply only 5vsb supply.

last time i did the hot test.. i kept the black probe at negative in large filter capacitor at input side and red probe at vcc pin.. now i am not sure if i kept it good.. oops.. but now i did as in post #13 i get 5v in vcc and 2 caps you suggested to check

[playit]

Re: mercury pc power supply only 5vsb supply.

now what should i check,could you also please tell me where should i keep the black probe and red probe ,because last time.. i took little help from youtube :P ,thanks for teaching me

[R_J]

Re: mercury pc power supply only 5vsb supply.

now what should i check,could you also please tell me where should i keep the black probe and red probe ,because last time.. i took little help from youtube :P ,thanks for teaching me

When checking voltages on the hot side, use the negative of the large cap or the negative of the bridge rectifier. In this case there are two large caps so you must use the one connected to the negative of the diode bridge, NOT the negative of the other large cap.
For cold side use the output ground

I gave some test points in post #14

[playit]

Re: mercury pc power supply only 5vsb supply.

oh ok, so whats next i should test now ? also the ic chip is good as per your 5 v test?

[playit]

Re: mercury pc power supply only 5vsb supply.

i tested the voltage at drive transformer point- its 0.72v and r23 both sides is 16.23 v

[R_J]

Re: mercury pc power supply only 5vsb supply.

i tested the voltage at drive transformer point- its 0.72v and r23 both sides is 16.23 v

There should be a jumper wire from R23 across to the trace that connects to the drive transformer, This 16v supplies the two transistors via the drive transformer.