Need help repair Sunshine ATX psu

[mikey5791]

Hi,

Got this el cheapo China made ATX psu Sunshine Model NS235W from a garage sale.
The owner does not know the psu condition. When I got home, since there is no sign of
burn marks and fuse tested with continuity, I plugged in to mains, I replaced the fuse
by a 60w light bulb and shorted the output green wire to black wire.

all I got is 5V DC from the purple and black output wire on the white plastic connector, I got No power from both the yellow 12V rail or the orange 3.3V rail. At first I suspect the primary side trans must have shorted. But using DMM diode test on the 3 trans with label C5027,and two trans with label C2335F shows no shorts.

The green thermistor SCK084 reads 10.6 ohm, this should be good as well.
Then I diode test on secondary side schotty diode with label PSR16C40CT and S10C40C
and DMM still show no shorts. My way of test is by putting black probe to middle pin, then red probe to left pin,then to right pin; DMM reads 79.

The two big Main caps measured 155VDC each. The 16 pin IC KA7500B reads 23.4VDC during
mains AC on while red probe to pin 12 and black probe to pin 7 ground.
I have replaced the small cap at C27,C33,C40 & C45 with low ESR same voltage type.
Also replaced 4 caps at yellow 12V rail, but only the 5VSTB power is on.

Then checking the C945 NPN trans,looking at the front side of tran,the left pin is emitter (E),
middle pin is collector(C), right pin is base(B), I unsolder the 3 trans from Q12,Q13,& Q7.
Testing by diode test,black probe to B,then red probe to E,red probe to C ;DMM reads infinite.
Then red probe to B,black to E; DMM=626 while black probe to C; DMM=624. I got almost
similar reading off circuit on all 3 trans.

What part/s is the next suspect to repair the no power from 12V and 3.3V rail? Appreciate for any help and thanks in advance.

 

[(*steve*)]

Is that 5V from the standby 5V lines?

If so, you need to enable the power supply. If you're already doing that then check the enable circuitry.

 

[(*steve*)]

You don't mention what the 60w bulb does. Does it light up at all?

 

[mikey5791]

Since the 5V is from probing purple and black wire at output, my guess is it is a standby 5V line. Do correct me if I am wrong.
How do I enable this power supply? Is it by switching on mains and disable the paper clip shorting the ps-on green wire and ground black wire at the 20 pins Molex main power connector. I do not know how to check the enable circuitry. Please show me how.

When I switched on 220V AC mains, the 60 watt bulb lights for about 2 seconds, then it
dims off and no light afterward. From past experience, this indicates there is no shorts from psu components.

The el cheapo ATX psu is meant for use on small project/test bench and I do not intend to use on data sensitive computer. I look forward for further help to revive it and gain the process as a learning experience. Thank you for your reply and hope for next step on repair.

 

[mikey5791]

Is anyone still reading this thread? As far as I know I have checked almost every part that is a suspect, but the result says it is "good"- as in within normal reading.
Kindly welcome any comment and advice. Thank you in advance.

 

[(*steve*)]

Do you have a circuit diagram for this PSU?

There is at least the possibility that the PSU turns on but then immediately turns off due to overvoltage. Adding a load on the rails may help.

The is also the possibility you're not jumpering the correct pins. Can you try it on another PSU?

Generally speaking, the correct procedure is to first apply power, then jumper the pins.

Sorry about not replying earlier. Thanks for the prod.

 

[HellasTechn]

How do I enable this power supply? Is it by switching on mains and disable the paper clip shorting the ps-on green wire and ground black wire at the 20 pins Molex main power connector. I do not know how to check the enable circuitry. Please show me how.

As long as the green wire is shorted to black your PSU should be fully on !

Is anyone still reading this thread?

Yes

As far as I know I have checked almost every part that is a suspect, but the result says it is "good"- as in within normal reading.
Kindly welcome any comment and advice. Thank you in advance.

It may be a bad controller chip. The one in red box.

Is it really worth it ? the monay you have spent for the parts you changed are probably more than to buy an other one that works.

 

[mikey5791]

Hi Steve,

1. Sorry I do not have a circuit diagram for this psu.
2. How do I check if there is overvoltage? I have try to connect an old harddisk
and use it as a load, but the psu is still not on.
3. I have tried the jumper method of green wire ps-on to black ground wire on other
psu and it always power on the fan and supply full 12V & 5V rail power.

Hi HellasTechn,

1. The controller chip is a 16 pin IC KA7500B. When I switched on mains,touch my
DMM red probe to pin 12 while black probe to pin 7 ground, the DMM shows 23.4 VDC. I attached the pdf file on KA7500B electrical characteristics which states VCC as 20V. Not sure if my reading of 23.4VDC is normal ?

 

[(*steve*)]

2. How do I check if there is overvoltage? I have try to connect an old harddisk and use it as a load, but the psu is still not on.

It's difficult. You've dome the right thing to try to load the power supply though.

let's see if @HellasTechn comes up with anything.

BTW, the 23.4V looks fine. The datasheet specifies a max of 42V, and a sensible range of 10V to 40V.

 

[mikey5791]

Hi,

This morning I decided to recheck transistor on heat sink 1 by setting my DMM to diode test. The transistor label is SEC-C5027 which is a NPN Silicon Transistor Main High Voltage Chopper Trans.(a 800V 3A collector current type).

Looking at front side of trans,left pin is Base(B),middle pin is Collector(C) and right pin is Emitter(E). Touching black DMM probe to B & red probe to C gives "1" infinite reading. Then moving the red probe to E still gives "1" infinite reading.
Then,swapping red probe to B & black probe to C also gives "1" infinite reading.
I believe the results show this trans is shorted.

Checking online for equivalent on C5027 yields just datasheet; so I am not too sure if my stock of trans such as ST13007 (300V 8A), STP20NM60FP(600V 20A), STPR10, SBL1060CT (60V 10A), P60N06A, P60NF or STPR1020CT(200V 10A) can be equivalent. I do not have stock of C5027 though and buying online for a part is too costly on shipping to our country.

Appreciate anyone willing to share input on which trans can be replacement for C5027. Thank you in advance.

 

[davenn]

Looking at front side of trans,left pin is Base(B),middle pin is Collector(C) and right pin is Emitter(E). Touching black DMM probe to B & red probe to C gives "1" infinite reading. Then moving the red probe to E still gives "1" infinite reading.
Then,swapping red probe to B & black probe to C also gives "1" infinite reading.
I believe the results show this trans is shorted.

infinite as in "OL" displayed, would indicate open circuit, not short circuit

if it was short it would show 0 (zero Ohms) or a few Ohms

 

[mikey5791]

Oops,sorry my mistake. If it is open circuit, meaning no current can flow through.
Is it still neccesary to change it for the psu to work ?

 

[davenn]

Oops,sorry my mistake. If it is open circuit, meaning no current can flow through.
Is it still neccesary to change it for the psu to work ?

yes, it wont be working either way

 

[mikey5791]

Took out the suspect C-5027 transistor off board and set my DMM to diode setting.
By looking at front side of trans(facing label C-5027),left pin is Base(B),middle pin is Collector(C) and right pin is Emitter(E) and using red probe as "+" and black probe as "-"
I got the following six readings:

+B&-E= 552
+E&-B=1
+B&-C=538
+C&-B=1
+E&-C=1 (suspect at fault)
+C&-E=1

The reading of 1 means over limit, the last pair of reading on E-C &C-E is questionable and at fault which I suspect the trans is open.

I have been checking online but there is no suitable equivalent I can use from my stock of ST13007, STP20NM60FP, STPR10, SBL1060CT, P60N06A, P60NF or STPR1020CT. How about using any of this as testing purpose just to check if the psu can revive. Any thought? Kindly advise. Thanks for any help.

 

[(*steve*)]

No, they ask seem to be what I would expect. I think you're barking up the wrong tree.

 

[mikey5791]

Steve,

Are you saying the readings are normal because my noob understanding is the C-5027 trans is open.
My intention is to change a new trans or something near its equivalent. Please correct me if I am wrong.

BTW, kindly guide me on which "tree" to bark as I am stumped at the moment.

 

[(*steve*)]

The readings you are getting are what I would expect from a working transistor.

What other possibilities have you investigated?

 

[mikey5791]

Hi,

Today I desoldered heatsink 2 and all the attached schottky rectifier so
I can test any suspect part off circuit.

Looking at left side part from front label MOSPEC S10C40C, I designate
left pin as A1,middle pin as C,right pin as A2 and set my DMM to diode test.

Red probe + to A1 & black probe - to C=reads 126
Red probe + to A2 & black probe - to C=reads 126
Red probe + to C & black probe - to A1=reads 1 (overlimit)
Red probe + to C & black probe - to A2=reads 1 (overlimit)

Looking at middle part from front label PHOTRON PSR16C40CT, I designate
left pin as A1,middle pin as C,right pin as A2

Red probe + to A1 & black probe - to C=reads 107
Red probe + to A2 & black probe - to C=reads 108
Red probe + to C & black probe - to A1=reads 1 (overlimit)
Red probe + to C & black probe - to A2=reads 1 (overlimit)

Looking at the right side double diode label FR302, on diode test I got one side reading as 1(overlimit), while the other side by swapping probes reads
406.

Still stumped at the above results which seemed to conclude all the three parts above are in normal range. So the problem of no power rail on 12V and 3.3V still lies somewhere else. Anyone has a clue? Many thanks for help.

 

[HellasTechn]

let's see if @HellasTechn comes up with anything.

I am sorry i was away for a long time. Let me read through the posts and see...

 

[ramussons]

Hi Steve,

1. Sorry I do not have a circuit diagram for this psu.
2. How do I check if there is overvoltage? I have try to connect an old harddisk
and use it as a load, but the psu is still not on.
3. I have tried the jumper method of green wire ps-on to black ground wire on other
psu and it always power on the fan and supply full 12V & 5V rail power.

Hi HellasTechn,

1. The controller chip is a 16 pin IC KA7500B. When I switched on mains,touch my
DMM red probe to pin 12 while black probe to pin 7 ground, the DMM shows 23.4 VDC. I attached the pdf file on KA7500B electrical characteristics which states VCC as 20V. Not sure if my reading of 23.4VDC is normal ?

Maybe this will be of some help.
http://danyk.cz/s_atx_en.html