Need help diagnose dead Sunshine ATX235 power supply

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi,

Anyone still reading this thread? Is this el cheapo chinese low quality psu worth the time to repair since I wish to use it as a learning experience; and it is not for use on any data sensitive pc. The likely usage will be for test bench on old 90's(Pentium 4) era motherboard.

FYI, the C945 driver transistor on Q12 base is connected to pin 11 on collector output of KA7500B while C945 driver transistor on Q13 base is connected to pin 8 on collector output of KA7500B. Earlier on testing them off circuit with a DMM on diode test gives a near identical (between 591 to 594 ohm) result from a new C945 unit.

Hoping to hear your generous and helpful reply. Thanking in advance.

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi,

This thread was posted about a month ago with limited response. I wonder if anyone still reading this? With my little knowledge I have tested almost every parts that I suspect to be at fault but the result doesn't seem to agree. I welcome any advice and do correct me if I am wrong.

Thank you in advance.

[Th3_uN1Qu3]

Re: Need help diagnose dead Sunshine ATX235 power supply

I am still reading, i just haven't noticed any activity in it lately.

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

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, STP20NM60FP, STPR10, SBL1060CT, P60N06A, P60NF or STPR1020CT can be equivalent. I do not have stock of C5027 though and buying online is too costly on shipping.

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

[budm]

Re: Need help diagnose dead Sunshine ATX235 power supply

NPN transistor: E-B junction Forward bias (red probe on B, black probe on E) test between E and B should show around 0.6V or so.
C-B junction forward bias: red probe on B, black probe on C, the meter should then show around 0.6V.
Meter showing 1 means over range, please read your meter manual. You should test the diode to see how the meter works when testing the diode, also read up on how to test transistor and diode.
Btw you should test the suspect device off the board. Right now your meter is showing you have open junctions.

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

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
+C&-E=1

The reading of 1 means over limit, I suspect the trans is open and is there a suitable
equivalent I can use from my stock of ST13007, STP20NM60FP, STPR10, SBL1060CT, P60N06A, P60NF or STPR1020CT.

[budm]

Re: Need help diagnose dead Sunshine ATX235 power supply

The readings are correct.
You need to look at how to test transistor and what the Transistor junctions are and how the transistor functions.
Get yourself a diode and do the test, you will get the same result as when you test the E-B, and C-B junction, and of course the E-C junction should show over limit (open circuit).
You will need to understand the device you are testing first then you will understand what the readings mean.
And BTW, testing the device with DMM is not 100% accurate but will give some clues because the applied Voltage is not the same as what the device is exposed to in the circuit.

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

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.

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi,
Reviving this old thread by desolder cap at C35 which is 1uF50v, tested esr is>4ohm.
So i replaced with a new cap of 1uF63v.

I force start the psu by shorting the green ps-on wire to ground. Then i switched on power.
The purple wire shows 5v as startup power. No other voltage like orange 3.3v or yellow 12v.
After about 5 minutes power on ,The fan start to spin. I got 3.3v,5v and 12v. Then i shut off power, restart power but fan not moving. Again i only got purple wire 5v and nothing else.

Can anyone help to explain why the psu slow to start up and kind to point me in what area to recheck. Thank you for advance help.

[Th3_uN1Qu3]

Re: Need help diagnose dead Sunshine ATX235 power supply

More bad capacitors, most likely. Try replacing the small capacitors on the secondary side.

[sam_sam_sam]

Re: Need help diagnose dead Sunshine ATX235 power supply

I also desoldered two small caps at C41 (2.2uF 50 V) & at C35 (1UF 50V) The small caps reads 3 ohm on ESR; are they alright?

It has been my experience that when you get an ESR value of more than 1.5 ohms this cap is bad compared to a new one with the same UF value

Most of the time I go by what the value of a new cap ESR compared to the cap that I am testing
and if I have any doubts about whether or not it good I just replace it

The value is about .900 to 1.3 ohms generally speaking

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi,
Going back to this old thread, i had removed capacitors considered bad with esr value exceed 1.3 ohm. Removed caps at c26,c45 and c35(all are 1uf50v) and at c41(2.2uf50v),c32(100uf25v) and c10(470uf16v).
The bad news is my stock of new caps are just type 22uf16v and 470uf35v. Can this new caps be used for those i removed?

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi,

Attached image of my stock of new caps.
Also image of front and back of the power supply after removing bad caps.
Appreciate any kind feedback.

[sam_sam_sam]

Re: Need help diagnose dead Sunshine ATX235 power supply

I also desoldered two small caps at C41 (2.2uF 50 V) & at C35 (1UF 50V) and the big coil. refer attached picture. The small caps reads 3 ohm on ESR; are they alright?

If you have this value for those caps they are way off the scale

It more like 1. Something ohms or lower than this

I would highly recommend that you replace those capacitor

And replace any capacitor that is lower than 100uf because they will probably have a high ESR value as well

This is just me but when I have problems with a switching power supply I replace all the capacitors except the main filtering capacitors

No you can substitute a higher value capacitor for those small UF value it probably will not work correctly

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi Sam (X3),

Very thankful for your reply. I am ordering online all the small caps which I removed. Also will post the result once all the small caps are installed.

Hope this ps full rail will work.

[mikey5791]

Re: Need help diagnose dead Sunshine ATX235 power supply

Hi, i received my new caps yesterday and replaced all caps of 100uf and lower to new ones. Switched on power and still can only get about standby 5v dc on the purple wire.
Not giving up, i took my DMM and remeasured output from primary side.
First i probe on main primary capacitor which is abt 155v dc on each cap. Next thing done is a huge mistake by setting my dmm to dc scale, put the red + probe on cathode of diode at D7(A on image) while black - negative probe on negative leg of main cap(B on image). I briefly saw the dc voltage reading of 862v but a pop on my dmm. Btw, is it possible to get such a high dc voltage? I know this is a huge mistake now as my dmm not able to detect any dc now....it just show (1) forever.
Can anyone point me what to do next to check on the psu? Thanks.