Need help repair dead AVF brand power supply

[mikey5791]

Hi All,

I got a dead AVF brand china made switching power supply from a friend recently who previously used in on a pc. It is labelled as a 350 watt power supply suitable for ATX type pc. I opened the case and did not find any burnt marks or bulged caps.

Before I make any further damage I connect a 100 watt light bulb in place of the 5A glass fuse. My country is using 220V as AC main. So I switch on the mains but still nothing happens, no fan turning and light bulb also not on.
At this stage I have no idea where else to check for the fault. Hope that someone with experience to diagnose power supply of this type can assist and guide me. On hand I have a digital multimeter, a digital capacitor meter and a 40 watt soldering iron with basic soldering skill.

Thanking in advance for any help and suggestion.

[Behemot]

Re: Need help repair dead AVF brand power supply

This is such an old crap I would not bother doing anything with that.

Most likely small caps are gone and if the fuse is burned than possibly primary silicon is blasted too.

[momaka]

Re: Need help repair dead AVF brand power supply

The PSU looks a bit cheap... probably only good to fix as a learning experience... but let's troubleshoot it anyways .

First, check if there is 5 VSB rail is there. That is check between purple wire and ground (i.e. black wire). Should be 5V +/-0.25V.

- If the 5 VSB rail is there, short the green wire on the ATX connector to ground and see if the PSU turns on. You may need to put a load on the PSU's 5V rail (that is, between any of the red wires and ground). Usually a 12 V car bulb or 12 V halogen bulb will work fine for that.

- If 5 VSB is not present, check the thermistor on the input. It is that green disk-shaped thingy next to the primary heatsink, right across from where the fuse was. It should read maybe 10 Ohms at most. If it is open-circuit or anything above 100 Ohms, it is definitely bad. The next item to check after that would be the bridge rectifier (in your case, the four diodes, next to that thermistor), followed by the transistors on the primary heatsink.

I'll stop here for now. Let us know what you find.

Also, this is not really a 350 Watt PSU. Probably 200 Watts at most with that primary heatsink (if even that). The lack of PI output coils will definitely let a big amount of ripple go through to the computer. I don't recommend you use this PSU with any piece of hardware you care much about.

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

Seeing the faulty ps is rather cheap, my intention is to try repair it and get learning experience but later to use it as a test bench; i will definitely not use as computer ps or any critical equipment.

As per your suggestion, I have not checked the 5VSB rail as my previous picture I had earlier short the green wire on the ATX connector to ground(black) but the PSU does not turn on. Can I still switch on main power 220V AC safely without burning any house fuse since I had removed (desolder six caps as mentioned below) and use mulitmeter to check on 5V rail?
I try to rule out the suspect one component at a time.From my attached pictures, I had desolder six(6) electrolytic caps from secondary side,then use my caps meter to check each of the caps,but the UF reading seems within 5% range as stated on caps. With power off, I checked resistance reading on the green thermistor SCK054,on scale 200ohm, the thermistor reads 6 ohm. This should still be good.

Then, I use diode range to check the four diodes next to the thermistor, each diode reads OL(over limit)on one side and about 594 ohm on other side. All four diodes should still be good. Next I try check transistors on primary heatsink but no idea how to do it.There are three transistors, my noob understanding is the left pin i assume is Gate(G),middle pin is Drain(D) and right pin is Source(S). I will use my digital multimeter on diode/continuity setting, first place the negative(-) black probe to Drain(D) while the positive red probe (+) on Source(S),next step is place the positive probe on Drain(D) and negative probe on Source(S),last step is place negative
probe on Drain(D) and positive probe on Gate(G).

On first transistor label C5353 2C, I got these readings:
-D&+S=739
+D&-S=1(over limit)
-D&+G=524
On second transistor label E13007 F2, I got these readings:
-D&+S=496
+D&-S=1(over limit)
-D&+G=540
On third transistor label E13007 F2, I got these readings:
-D&+S=490
+D&-S=1(over limit)
-D&+G=542

Does the above readings says anything important about the transistors on primary heatsink, whether they are still good. I haven't do any test on transistors on secondary heatsink yet. waiting further help.

Hope my above simple tests can assist to further narrow down the ps fault.
Thank you for kind feedback.

[momaka]

Re: Need help repair dead AVF brand power supply

As per your suggestion, I have not checked the 5VSB rail as my previous picture I had earlier short the green wire on the ATX connector to ground(black) but the PSU does not turn on. Can I still switch on main power 220V AC safely without burning any house fuse since I had removed (desolder six caps as mentioned below) and use mulitmeter to check on 5V rail?

As long as you have the incandescent light bulb in place of the fuse, you can still apply 220 V AC power. Just do NOT short green wire to ground on ATX connector, because the caps you have removed are for the output. The PSU will not like it.
However, the 5 VSB rail (purple wire) will come on as soon as you plug in 220 V AC into the PSU. And it looks like you didn't remove the caps for that, so plug in the PSU and see if you get 5V on purple wire. If NO, then that would prevent the PSU from turning ON. If YES, then I will explain troubleshooting in more detail later.

With power off, I checked resistance reading on the green thermistor SCK054,on scale 200ohm, the thermistor reads 6 ohm. This should still be good.

Yes, thermistor is good.

Then, I use diode range to check the four diodes next to the thermistor, each diode reads OL(over limit)on one side and about 594 ohm on other side. All four diodes should still be good.

Correct.

Next I try check transistors on primary heatsink but no idea how to do it.There are three transistors, my noob understanding is the left pin i assume is Gate(G),middle pin is Drain(D) and right pin is Source(S). I will use my digital multimeter on diode/continuity setting, first place the negative(-) black probe to Drain(D) while the positive red probe (+) on Source(S),next step is place the positive probe on Drain(D) and negative probe on Source(S),last step is place negative
probe on Drain(D) and positive probe on Gate(G).

You were close .
That's the correct testing procedure for a MOSFET. What you have in your PSU is Bipolar Junction Transistors (BJTs). In particular, those transistors are NPN type.

Generally, TO-220 case BJTs (like the ones one your heatsink) have left pin as Base (B), center pin as Collector (C), and right pin as Emitter (E) - that is, if you are looking at the transistor from the text side.

The way you test NPN BJTs is you set multimeter to diode test. Then put multimeter positive (+) probe on Base and negative (-) probe on Collector (C). See if you get a reading between 500-750 mV (or 0.5 to 0.75V depending on how your multimeter counts) - that would indicate a good transistor. Less than 100 mV (or 0.1V) indicates likely bad transistor.

Now repeat that step above again, but this time with multimeter positive (+) probe on Base and negative (-) probe on Emitter (E). You should get the same or very similar readings again.

On first transistor label C5353 2C, I got these readings:
-D&+S=739
+D&-S=1(over limit)
-D&+G=524

That transistor is likely good.

In particular, that last reading, "-D&+G=524", is essentially the same as +B&-C, which will yield between 500 and 750, as I mentioned above.

On second transistor label E13007 F2, I got these readings:
-D&+S=496
+D&-S=1(over limit)
-D&+G=540
On third transistor label E13007 F2, I got these readings:
-D&+S=490
+D&-S=1(over limit)
-D&+G=542

Likely good too.

Still, do the prpcedures I mentioned above, just to confirm (and learn to test BJTs? )

I haven't do any test on transistors on secondary heatsink yet.

The "transistors" on the secondary heatsink are actually schottky rectifiers (two diodes with anodes on the outer pins and a common cathode on the center pin). Google their part numbers, and you will see what I mean .

Thank you for kind feedback.

You are welcome!

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

As you suggested,I removed the short wire connect green wire to ground on ATX connector,then plug in 220v AC, touch my multimeter red positive probe to purple wire and black negative probe to black ground on ATX connector. The multimeter is set to DC range but still zero reading. Am I doing the correct way?

Next by following your procedures on testing BJTs, I got the following results:
(+ is positve red probe,- is negative black probe,1 is base,2 is collector,3 is emitter)
On first C5353 2C
+1&-2=528 while +1&-3=556

On second E13007 F2
+1&-2=544 while +1&-3=556

On third E13007 F2
+1&-2=547 while +1&-3=557

Are the above results indicate BJTs are good? Many thanks for your simple procedure. Now I am learning a new troubleshooting skill.

Do we go on testing schottky rectifiers? I am not sure how to go about on this. The first and third rectifier are labeled FMB26L(60V Schottky) while middle one is BY028E 200 PHV0201 (no info on this).

Hoping for continued assistance and your kind patience as I am a slow learner. Thank you and much appreciated.

[momaka]

Re: Need help repair dead AVF brand power supply

As you suggested,I removed the short wire connect green wire to ground on ATX connector,then plug in 220v AC, touch my multimeter red positive probe to purple wire and black negative probe to black ground on ATX connector. The multimeter is set to DC range but still zero reading. Am I doing the correct way?

Almost.
There is NO need to short green wire to ground when testing voltage on purple wire (5 V stand-by rail, or 5 VSB as it is often called). 5 VSB should come up to 5V as soon as the PSU is plugged in, regardless of anything else.

The fact that you don't see 5V on purple wire indicates a problem. It means the 5 VSB supply is not working. So this is what we must troubleshoot first.

The 5 VSB supply consists of that C5353 transistor, the small transformer labeled "MTREE-19-1", and the components around it. I am using this picture as a reference:
https://www.badcaps.net/forum/attach...0&d=1444016456

In particular, there are two black diodes (next to a 100 Ohm resistor) below that "MTREE-19-1" transformer. Test them with your multimeter and let me know what you get. One of them appears to have overheated near its leads.

Are the above results indicate BJTs are good?

Yes.

Do we go on testing schottky rectifiers? I am not sure how to go about on this. The first and third rectifier are labeled FMB26L(60V Schottky) while middle one is BY028E 200 PHV0201 (no info on this).

We don't need to test them at this point, since we first must troubleshoot the 5VSB circuit.

However, if you still want to test them, I will give you the procedures.
For the FMB-26L and BY028E, the two outer pins on each device are the anodes (A). The middle (center) pin is common cathode (C).
To test, set multimeter to diode setting. Put positive (+) probe on one of the outer pins (A) and negative (-) probe on center pin (C). You should get a reading between around 200 and 750. Now take the positive (+) probe, and put it on the other outer pin (again, A), and negative (-) probe on center pin (C). You should get the same reading again.

Note: cheap power supplies sometimes have "dummy" load resistors on their 3.3V/5V/12V rails. These resistors can be as low as 10 Ohms. Therefore, the test above may be affected by these resistors and you can get lower readings. So don't panic if you get a low reading below 200. Just note it down, as we might have to check it again later.

Hoping for continued assistance and your kind patience as I am a slow learner. Thank you and much appreciated.

No problem. You are doing quite well, actually . And don't worry. Power supplies are easy, once you get the basics.

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

As per your procedure, I tested the two black diodes namely the first diode (nearest to a 100 ohm resistor) got label "50" reads 1(over limit)on one end and 924 on the other end. The other diode label "24" reads 1(over limit)on one end and 003 on the other end. (too low?) Suspect this diode is roasted. For reference, I attached pic of img1010 on the two black diodes.

BTW, I follow your guide on testing schottky rectifier using + for positive red probe and - for negative black probe, A1 as the left anode pin, A2 as the right anode pin and C as the middle cathode pin.
The results are as follows:

On left side FMB26L
+A1 & -C= 45
+A2 & -C= 45

On middle BY028E
+A1 & -C= 146
+A2 & -C= 146

On right side FMB26L
+A1 & -C= 10
+A2 & -C= 10

Does the results mean anything ?

SPECIAL NOTE: about a few days ago I had try a power up but didn't notice any glow. Last night, out of curiousity I replaced the 100 watt bulb with a 60 watt (the six caps still off circuit and short wire connecting the green wire to ground on ATX connector removed) and try a power up in a dark room. Voila! I got SLIGHT GLOW lasting like 2 seconds then no glow later. Is this a good sign? My noob knowledge is the series light will glow with full brightness if there is a short. It is a silly mistake before this I was working under normal light making it hard to notice slight glow. (LOL)

Your assurance that power supplies are easy really encouraged me to go further on this troubleshooting. Hoping to seek your helpful procedures and expert advice.

Thank you.

[everell]

Re: Need help repair dead AVF brand power supply

momaka: It looks to me like he has the black wire (Line) going to the neutral side of the AC connector, and the white wire (Neutral) going to the Line side of the AC connector. On the pc board, looks like the black going to Line and white going to Neutral properly. Can you verify this? This could create safety problem.

[eddwhatley]

Re: Need help repair dead AVF brand power supply

Your country . . .USA

125V AC line voltage

White wire . . .the color of safety . . . . . ..COLD side
Black wire . . . the color of DEATH . . . . . .HOT side
Green wire . . .the color of green grass . .the earth . . . Ground


His country . . Malaysia

220-230 AC line voltage

White wire . . . . the color of safety . . ..cold side
Black wire . . . . the color of INSTANT DEATH . . . at 230VAC !

edd

[stj]

Re: Need help repair dead AVF brand power supply

lol

reminds me of ford cars.
brown = earth (or dirt or something!)

[momaka]

Re: Need help repair dead AVF brand power supply

SPECIAL NOTE: about a few days ago I had try a power up but didn't notice any glow. Last night, out of curiousity I replaced the 100 watt bulb with a 60 watt (the six caps still off circuit and short wire connecting the green wire to ground on ATX connector removed) and try a power up in a dark room. Voila! I got SLIGHT GLOW lasting like 2 seconds then no glow later. Is this a good sign? My noob knowledge is the series light will glow with full brightness if there is a short.

Even with the 100 watt bulb, you should still have seen a very very quick dim glow.

Try this:
put the caps back in the PSU and plug in power with the 60 watt bulb in series. After the light glows and goes off, see if you get 5V on the purple wire with your multimeter. I just want to verify this one more time before we proceed.

And yes, light bulb will glow and stay glowing if something is very wrong with the PSU. But in your situation, I think the PSU has a small problem preventing it from working.

The results are as follows:

On left side FMB26L
+A1 & -C= 45
+A2 & -C= 45

On middle BY028E
+A1 & -C= 146
+A2 & -C= 146

On right side FMB26L
+A1 & -C= 10
+A2 & -C= 10

Does the results mean anything ?

Yes, it means there are "dummy" load resistors on the output of the 3.3V, 5V. 12V rail. Looks like the dummy load resistors are:
10 Ohms for 3.3V rail (resistor color code: brown, black, black, gold)
47 Ohms for 5V rail (resistor color code: yellow, purple, black, gold)
150 Ohms for 12V rail (resistor color code: brown, green, brown, gold)

And you can see them in this picture:
https://www.badcaps.net/forum/attach...2&d=1444485096

I think that would be R304, R305, and the resistor by the blue wire. So the results for the diode rectifiers above are inconclusive. To test the diode rectifiers, you must either remove the dummy resistors or remove the rectifiers themselves. I think it would be easier to remove the resistors.

But let's not worry about that for the moment. First thing is to get 5V on the purple wire. Without it, nothing will work on the power supply.

As per your procedure, I tested the two black diodes namely the first diode (nearest to a 100 ohm resistor) got label "50" reads 1(over limit)on one end and 924 on the other end. The other diode label "24" reads 1(over limit)on one end and 003 on the other end. (too low?) Suspect this diode is roasted. For reference, I attached pic of img1010 on the two black diodes.

Remove that "24" diode from the board and test it out of the circuit again. The reading you got for it in the circuit is not quite right (but not obviously wrong either). It is strange to have it test very low in one direction (the 003 reading you got) and over limit on the other.

[momaka]

Re: Need help repair dead AVF brand power supply

momaka: It looks to me like he has the black wire (Line) going to the neutral side of the AC connector, and the white wire (Neutral) going to the Line side of the AC connector. On the pc board, looks like the black going to Line and white going to Neutral properly. Can you verify this? This could create safety problem.

Yes, you are absolutely right.
It looks like the wires were soldered incorrectly at the factory. Unfortunately, this is not the first time I have seen this!

Either way, as long as ground is connected, this should not be that much of a safety problem (in Europe, for example, the Schuko plug has ambiguous polarity - its L and N contacts can be reversed).

The real possible safety problem with this power supply is the ceramic caps used in the line input filter as Y-caps. Real agency-approved Y-caps will go open-circuit in case of failure, whereas these ceramic caps might go short-circuit. This is where it is critical that the Live wire be across the fuse.

reminds me of ford cars.
brown = earth (or dirt or something!)

lol . I thought brown and light blue are the standard colors in Europe for Neutral and Live respectively.

[ChaosLegionnaire]

Re: Need help repair dead AVF brand power supply

err i thought brown=live and blue=neutral. lol u made me look at my 3 pin plug just to make sure...

also, u said this psu has no pi filters eh? i'd bet that psu weighs as light as a feather as im asserting the weight of the pi filter coils take up quite a bit of a psu's weight? the layman's saying is also that you judge a psu by its weight.

so if my assertion is right, there is indeed truth to the saying that the heavier the psu, the better.

[stj]

Re: Need help repair dead AVF brand power supply

brown = live (death)
blue = neutral,
green&yellow = earth.

[TELVM]

Re: Need help repair dead AVF brand power supply

. . . . . . . . . .

[momaka]

Re: Need help repair dead AVF brand power supply

I guess I was wrong then .

But why have brown = live? If anything, bright-blue should be live so that you can see it. Plus, that color makes me think of electric sparks - i.e. don't touch. Ford should be applauded: brown = earth (dirt) = ground. Makes 100% sense to me .

[stj]

Re: Need help repair dead AVF brand power supply

BMW also use brown = earth.
i just checked.

[Scorpent]

Re: Need help repair dead AVF brand power supply

I guess I was wrong then .

But why have brown = live? If anything, bright-blue should be live so that you can see it. Plus, that color makes me think of electric sparks - i.e. don't touch. Ford should be applauded: brown = earth (dirt) = ground. Makes 100% sense to me .

In Britain,(I think), red used to be live. Then colorblind people saw red as another colour. So they changed it to brown.

[stj]

Re: Need help repair dead AVF brand power supply

old code:
red = live
black = neutral
green = earth

new code:
brown = live
blue = neutral
green&yellow = earth

also when the new colours came in, they banned the use of figure-8 / bell wire for mains use.
stuff like table-lights had to use flat double-insulated cables with the new colours in them.