Need help repair dead AVF brand power supply

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

Referring to your earlier suggestion, I removed the 2nd diode label "24" from board and test it off circuit and finally saw the diode labelled CT(first row) SB240(second row). I used diode range and it read 001(beeps) at one end and swap probes and get 001(beeps) the other way. The result seem to point this diode is shorted. Is this a schottky diode 40 Volt 2.0A type? The nearest diode stock that i have is a LT116(first row)2A05(second row) which gives a peak repititive reverse voltage of 600V and average rectified output current of 2.0A. Can I use this to replace the shorted CT SB240 ?

I have not put back the six removed caps in the PSU due to waiting replacement of the above shorted diode. Once this diode is replaced and the six caps soldered on pcb and put a load(maybe a 12V DC fan will do ?) and the series 60W bulb still connected, is it time to power up AC to see if the 5V purple wire will output 5v DC?

Appreciate all the feedback and suggested points on the troubleshoot.
Thank you all.

[momaka]

Re: Need help repair dead AVF brand power supply

Referring to your earlier suggestion, I removed the 2nd diode label "24" from board and test it off circuit and finally saw the diode labelled CT(first row) SB240(second row). I used diode range and it read 001(beeps) at one end and swap probes and get 001(beeps) the other way. The result seem to point this diode is shorted. Is this a schottky diode 40 Volt 2.0A type?

Correct.
That diode is bad. And yes, it is a 40 V, 2 A, schottky type.

The 2A05 diode you have may work or it may not work. Reason I say that is because the circuit operates at high frequency. 2A05 is a general purpose diode, so it might not work. Generally, you need either schottky or fast recovery diode. If you have any of these diodes, they will probably work okay for testing
PR1001 through PR1007
HER201 through HER208
BA157 through BA159
FR153
There are many others that could work as well, but these are very common in power supplies, so look through your junk pile if you have one .

--- OR ---

We can do this:
That diode with the "50" label that is nearest to the 100 Ohm resistor - remove it and put it in place of the SB240 diode. (Why? I will tell you at the end of the post below)
Then...

I have not put back the six removed caps in the PSU

That's fine.

You actually don't need all six to test the 5 VSB. Just put back the large one closest to the purple wire. I think that is for the 5 VSB. The you can plug power to the power supply. No need to put a load. The 5 VSB should come right up. Just DO NOT short green wire to ground!
Use the 60W light bulb.

.

... And now for the explanation behind putting the "50" diode in place of the shorted SB240...
Every computer power supply actually has two power supplies inside it: the 5 VSB supply and the main supply. 5 VSB provides 5V to the computer all of the time - that is, it doesn't matter if the PC is running (ON) or not (OFF/Standby/Sleep/Hibernate). The main supply provides 3.3V, 5V, 12V, and -12V *only* when the computer is running (ON).

Now, the main power supply in your PSU is a half-bridge design. This is evident by the 3 transformers in the middle and the PWM chip, which is usually KA7500, TL494/KBL494, SG6105, or AT2005 (and in case of Deer/L&C power supplies: DR0183, "2003", or "2005").

In a PSU with a half-bridge design, the 5 VSB power supply actually has two rails: 5 V standby (5 VSB) and a secondary auxiliary rail, which is usually between 10-25V. The secondary auxiliary rail is for providing power to the PWM chip (i.e. the KA7500, TL494, or SG6105). The SB240 schottky diode you removed appears to be for the 5 VSB rail, whereas the "50" diode is likely for the secondary auxiliary rail. Since we interested first in only testing 5 VSB rail, we do not really need to have the secondary auxiliary rail. The 5 VSB circuit is self-oscillating and does not depend on the PWM controller to run. That's why you can use the "50" diode in place of the SB240 diode for testing purposes.

Once we determine that 5 VSB is running, then you can put that "50" diode back in its original place and replace the SB240 diode with a proper replacement.

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

Your detailed explanation on 5VSB is simple and easy to understand. Yet it has encouraged me a lot to go on and find the faulty component.
For the purpose of testing, I used the LT116 2A05 (got from a TV junk board) in place of SB240. Eventhough it is just a general purpose,this is the nearest diode to SB240 that I can find. I also replaced all the six electrolytic caps on board (four are new caps)-refer image 1020. No load being used and no short green wire to ground. On power up AC through 60watt bulb in series, and set my multimeter on DC range,I put black probe on black pin ATX connector while red probe on purple wire gives a reading of 5.0V DC.refer image 1024. Wow! I was excited now there is some life here.... Is this a good sign? I think this should be good and getting better.

Hoping for next step on diagnosing further and getting the PS to working condition soon. Thank you for your patience.

[momaka]

Re: Need help repair dead AVF brand power supply

For the purpose of testing, I used the LT116 2A05 (got from a TV junk board) in place of SB240. Eventhough it is just a general purpose,this is the nearest diode to SB240 that I can find.
...
On power up AC through 60watt bulb in series, and set my multimeter on DC range,I put black probe on black pin ATX connector while red probe on purple wire gives a reading of 5.0V DC.refer image 1024. Wow! I was excited now there is some life here.... Is this a good sign?

Yes, that is a good sign indeed .

I guess you can leave the 2A05 diode in there for now, until the whole PSU is determined working (later you can replace it with something better - i.e. schottky or fast recovery type).

So, the next step is... short green wire to ground and see if the power supply comes on . If not, let me know what happens.

Also, keep the 60W incandescent bulb in series with the power supply until the power supply is completely fixed (I will let you know when we get there) and we determine that everything works and nothing overheats or makes strange noises.

I also replaced all the six electrolytic caps on board (four are new caps)-refer image 1020.

The brown caps with "KZH" (or "KZM") text are good - if they are genuine Chemicon, that is. There are many counterfeit caps, so beware of that. The "JWCO" caps are quite terrible. Probably general purpose too, so don't expect them to last. But I guess if you are not going to be using this PSU in a computer or to power anything expensive, then that is okay.

Also, to make the new caps last a little bit longer, the "dummy" load resistors will have to get rearranged somewhat. They generate too much heat near the capacitors right now, and that will bake the new capacitors too, eventually. I will explain in more detail once we get the PSU working. For now, you need not worry about this.

And lastly, you said you took that 2A05 diode from a dead TV board? Do you still have the dead TV board? And do you have access to more dead TV boards? Reason I ask is because sometimes they often have good components on them (and filter chokes too, most importantly ).

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

From the step you mentioned, after I short green wire to ground while still keep the 60W bulb in series; the light bulb glow then off in less than 2 seconds but this time the psu fan spins!!

Excitedly I took out my DMM and make some DC voltage test, on the molex ATX connector probe on red and black wire I got 5.0V, on yellow & black wire I got 11.7V (slight low from expected 12 V) while on orange & black I got 3.1V (slight low from expected 3.3V). After switching on for 10 minutes, the psu fan still spinning and I don't hear any strange unusual noise. Hopefully nothing else overheats.(image 1029 attached)


You are saying to rearrange those "dummy" load resistors as they generate too much heat near the caps. May I know how to go about this?
I will take note on the "JWCO" as general purpose caps and the 2A05 diode as temporary, will replace these once I got budget for the better type.

As I recalled I took the 2A05 diode from a dead tv board (image 1027). From this board I expect some reusable components which I can extract in future are the fuse,ceramic resistor,transistor and coil. Do I left out anything important?

Waiting for your further guidance in making the PSU completely fixed and to finally remove the 60W bulb in series. Thank you for all the help.

[momaka]

Re: Need help repair dead AVF brand power supply

Excitedly I took out my DMM and make some DC voltage test, on the molex ATX connector probe on red and black wire I got 5.0V, on yellow & black wire I got 11.7V (slight low from expected 12 V) while on orange & black I got 3.1V (slight low from expected 3.3V). After switching on for 10 minutes, the psu fan still spinning and I don't hear any strange unusual noise. Hopefully nothing else overheats.(image 1029 attached)

Seems to be working good, then .
The voltage readings you got for the 3.3 V and 12 V rails are normal, because the PSU is not loaded. When you put a bigger load on the 5 V rail (and some on the other rails too), they will get much closer to their respective values.

You are saying to rearrange those "dummy" load resistors as they generate too much heat near the caps. May I know how to go about this?

Well, it seems like the dummy load resistors are:
10 Ohms for 3.3V rail (resistor by the blue wire?), color code: brown, black, black, gold)
47 Ohms for 5V rail (R305?), color code: yellow, purple, black, gold)
150 Ohms for 12V rail (R304?, by the yellow wires), color code: brown, green, brown, gold)

I am using this picture as a reference:
https://www.badcaps.net/forum/attachm...2&d=1444485096

So perhaps double check me on that. See if those resistors are indeed wired to those rails. Also, you can set your multimeter to lowest resistance scale (200 Ohms) and measure resistance between the following:
3.3 V rail and ground
5 V rail and ground
12 V rail and ground

Now, what I generally like to do is keep all power dissipation by each dummy resistor less than half of their rated wattage and less than 0.6 Watts, if possible.

The formula for calculating how much power each resistor is drawing is as follows:
P = (V^2) / R
Where P is power in Watts, V is the voltage across the resistor (i.e. 3.3 V, 5 V, 12 V, and etc.), and R is the resistance of the resistor.
So let's say the 12 V rail does indeed have a 150 Ohm resistor. Then that resistor will be dissipating
P = (12 Volts ^2)/150 Ohms = 144 / 150 = 0.96 Watts <- which is a bit high

The dummy load resistors in your PSU appear to be rated for 1 Watt and 2 Watts.

The easiest thing you can do (assuming the dummy resistors are indeed 10, 47, and 150 Ohms) is remove the 10 Ohm resistor from 3.3 V rail and put the 47 Ohm resistor from the 5V rail there. Then, remove the 150 Ohm resistor from the 12 V rail and put it on the 5V rail. For the 12V rail, see if you can find a resistor that is 270 Ohms or more. If it is 270-470 Ohms, make sure to use a 1 Watt-rated resistor. Between 470 and 1 KOhm, you can use 1/2 Watt resistor, and above 1 KOhm, you can use 1/4 Watt resistor. See what your TV board has. Look for the bigger resistors.

Also, if for some reason the PSU starts to squeal after moving those resistors around like I mentioned, this is perhaps because it needs a bigger load. Most cheap PSUs will work fine. But the higher-power ones will want a bigger load and may even have unstable voltages. So check after performing any mods and before using the PSU for a project.

As I recalled I took the 2A05 diode from a dead tv board (image 1027). From this board I expect some reusable components which I can extract in future are the fuse,ceramic resistor,transistor and coil. Do I left out anything important?

That whole board is a gold mine if you are looking for general repair components.

I see lots of big resistors and caps on it. The caps are general purpose rated for 85C, but in a pinch, you can definitely use them to test something that has visibly-failed electrolytic caps. The big 400V caps is another cool "toy" to have in your parts box. Same with the flyback. The opto-coupler is good to have too... really, I'd save the whole board.

In fact, there should definitely be a fast-recovery type diode somewhere on it - perhaps that big diode to the left side of that big yellow transformer.

Also, you see that coil with the label "YDD_ET24"? That is a common-mode choke - very useful part to put in a PSU (like the one you are working on) that doesn't have it. It filters voltage spikes coming from the line voltage. The square blue capacitors next to it are safety X-class caps. These, too, are use for filtering voltage spikes and reducing EMI (electromagnetic interference) that the PSU produces. Both of these can be inserted on your PSU, but you would have to re-arrange a few components on the board where the input wires and fuse go.

However, I don't know how much further time and effort you are willing to spend with this PSU, so I will stop here. If you would like to try and improve the PSU further for learning purposes, let me know and we can continue from here.

Waiting for your further guidance in making the PSU completely fixed and to finally remove the 60W bulb in series. Thank you for all the help.

You are welcome.
At this point, if you are not going to do further mods on the power supply, you can put back the fuse and remove the light bulb.

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

From your comment, I rechecked those 3 dummy load resistors and confirmed color of resistors are correct ,using diode test and measured the resistors as 10 ohm(3.3V rail),46 ohm(5V rail) & 146 ohm(12V rail). Then I set my multimeter to lowest resistance scale (200 Ohms) and measure resistance between the following:
3.3 V rail and ground= reading 10.5 Ohm
5 V rail and ground=reading 47 Ohm
12 V rail and ground=reading 149 Ohm

FYI, I have not removed or rearranged any of the dummy load resistor as I am still looking for a suitable one to put on the 12V rail. So far I am unable to get a resistor of 270-470 Ohm of 1 watt except a resistor of color:blue,green,brown,gold which is about 650 Ohm. (image 1030)
Since this resistor is slight smaller in size, I think it should be rated at 0.5 watt. Anyway I hope we can use this as replacement for 12V rail use.
I also attached latest picture of the front whole board (image 1039) and the back of the board (image 1042) for reference.

My wish is to continue improve this PSU and gain learning experience at the same time. No hurry though as learning process takes time. Since you mentioned about getting lots of useful parts from the dead tv board, I am interested to know how to install common choke/coil and square blue cap to filter voltage spikes & reduce EMI on this PSU. All these terms are very new to me. Should we start modify on the initial filter stage (like from AC main) as I noticed on my top board left corner near the 60W bulb in series connection there seems to be some empty space. (refer image 1032 for front pic, image 1043 for back pic while image 1042 is the whole back board). I suspect the empty space is left for future upgrade.

Look forward to your kind assistance soon.

[BleedCap]

Re: Need help repair dead AVF brand power supply

I suspect the empty space is left for future upgrade.

More like for cost cutting.

[momaka]

Re: Need help repair dead AVF brand power supply

FYI, I have not removed or rearranged any of the dummy load resistor as I am still looking for a suitable one to put on the 12V rail. So far I am unable to get a resistor of 270-470 Ohm of 1 watt except a resistor of color:blue,green,brown,gold which is about 650 Ohm. (image 1030)
Since this resistor is slight smaller in size, I think it should be rated at 0.5 watt. Anyway I hope we can use this as replacement for 12V rail use.

I think that resistor has colors blue, gray, brown, gold... i.e. 680 Ohms, 5% tolerance. It should work.

Like I said, in worst case, if PSU is not happy with the new dummy resistors and it whines or voltages are unstable, you can always put back the dummy resistors in their original positions .

Since you mentioned about getting lots of useful parts from the dead tv board, I am interested to know how to install common choke/coil and square blue cap to filter voltage spikes & reduce EMI on this PSU. All these terms are very new to me. Should we start modify on the initial filter stage (like from AC main) as I noticed on my top board left corner near the 60W bulb in series connection there seems to be some empty space. (refer image 1032 for front pic, image 1043 for back pic while image 1042 is the whole back board). I suspect the empty space is left for future upgrade.

Yes, that empty space is where the EMI/RFI filtering goes (RFI = radio frequency interference). However, the PSU manufacturer didn't leave it empty as a future upgrade . Rather, they left it because they are cheap and wanted to save money, as BleedCap said. This is very typical of low-quality power supplies. A switch mode power supply should always have EMI/RFI filtering. Generally, it is good to have two X caps, two Y caps, and two common-mode chokes. However, having even only one X cap and one choke is much better than nothing.

I drew a diagram where you can place the components. You can see it here:
https://www.badcaps.net/forum/attach...1&d=1445562920

Let me know if you have any questions. Also, make sure to install the common mode choke the right way - that is, if you install the choke and after that you get continuity or low resistance between Live and Neutral on PSU input wires, it is wired WRONG WAY.
So just in case, test PSU with light bulb in series after installing those components so that you don't blow your fuse or NTC (thermistor).

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

Glad you took the time to draw a diagram on the components placement.
It is clear and easy to follow. However, with my limited knowledge I do have a few questions:

1. After I pulled the X (square) caps from the dead tv board, how do I test for good part? I think it is rated X2 with 0.1 uF or 1uF(not sure yet). Can I test with a capacitor meter and is it suffice?

2. The size of original 5A 250V glass fuse(removed earlier) can't seem to fit into the new fuse proposed area. Refer image 1060 for length comparison. What should I do? Can I attach a new longer wire and solder to fuse each end, then insulate properly against touching other parts? or any simpler way pls teach me.

3. I got one extra thermistor (MF72-2 7RM) look like a 4A 8 ohm type and 8 pieces of many sizes coil. Refer image 1062. Can I use any of this on those empty area marked in red L302,L303 or L304 (refer image 1053)? Or can I use any of those extra part on empty area like in CY103,PFC2 or V101 (refer image 1055 upper right corner)

Again I look forward to your advice and comments in making this PSU working better. Appreciate with many thanks.

[momaka]

Re: Need help repair dead AVF brand power supply

1. After I pulled the X (square) caps from the dead tv board, how do I test for good part? I think it is rated X2 with 0.1 uF or 1uF(not sure yet). Can I test with a capacitor meter and is it suffice?

Judging by the size of that X2 cap, it is probably 0.1 uF. Yes you can check it with capacitance meter, and that's it. These don't go high ESR, unlike electrolytic capacitors. However, if the X2 cap saw many voltage spikes during its life, it may have lost some capacity. And some can even become shorted (though, it is usually rare and depends on the brand).

2. The size of original 5A 250V glass fuse(removed earlier) can't seem to fit into the new fuse proposed area. Refer image 1060 for length comparison. What should I do? Can I attach a new longer wire and solder to fuse each end, then insulate properly against touching other parts?

Yes, soldering a longer (solid) wire on one end is precisely what some manufacturers do.
In the picture below, you can see how I soldered a new fuse in place of the old one and wrapped it in black electrical tape (next to those coils that have green paint on them).
https://www.badcaps.net/forum/attach...6&d=1440088269
Speaking of the green paint, I didn't do it. PSU was given to me for repair like that. You can see the entire post here if you are interested: https://www.badcaps.net/forum/showpo...&postcount=233

Anyways, I would also like to point out to you not to heat the fuse for too long. Just long enough to solder the wire well on it.

3. I got one extra thermistor (MF72-2 7RM) look like a 4A 8 ohm type and 8 pieces of many sizes coil. Refer image 1062. Can I use any of this on those empty area marked in red L302,L303 or L304 (refer image 1053)? Or can I use any of those extra part on empty area like in CY103,PFC2 or V101 (refer image 1055 upper right corner)

Not in those areas, no.

Your PSU already has one termistor, so you don't really need a second one. Just keep it as a spare. Sometimes when a power supply blows its fuse, it can also blow the thermistor. If you plan to service more power supplies, this extra thermistor might come handy in the future.

As for the 8 coils/inductors you took a picture of: they all have too thin of a wire, so you can't use them in spots L302, L303, or L304. If you want to put inductors in those spots, you can make your own from thick solid copper wire (the same that is used on the big round inductor near the output capacitors). Just wind 10-15 turns on a round object with 4-5 mm diameter. Then remove the object and you have a air-core inductor. Air-core inductors have a pretty low inductance, but it's better than nothing.

Also note that L303 and L304 have jumper wire in theirs spots, but L302, the wire is connected differently. If you do install inductors in those spots, you need to remove the jumper wire and install the inductor in the place of the jumper wire (i.e. same holes).

That said, those inductors you pulled from the TV aren't useless. The one on the far right with "203950" text looks like a single-mode choke. Sometimes, PSUs will use both single and common mode chokes on their input. Unfortunately, your power supply doesn't have any more space. But you should certainly save it in case you get another PSU like this that has nothing on the input.
Also, the 3rd inductor from left to right could be used for the 5 VSB or -12V rail. However, this PSU appears to have one for the 5 VSB already. So just save that one too. In fact, save all of them for now. If you ever come to a situation where you really need a specific inductor but don't have it, you can unwind one of those inductors and wind your own with thicker or thinner wire, as desired.

Lastly, to answer your questions about CY103, PFC/PFC2, and V101/V102...

CY103 is where a Y2 safety cap would go. I think those circular blue caps near where you pulled the square X2 cap from the TV board, should be Y2 safety caps. Might need to post pictures of them, though.

PFC/PFC2 is where the manufacturer can install a passive coil for Power Factor Correction (PFC). A PFC coils is basically a very large inductor. It makes the PSU appear more "resistive" to the power lines, which can help a little bit with power distribution if you live in a remote location far from the sub-station or pole transformer for your house.

Finally, V101/V102 - those are likely spots for varistors (commonly known as MOVs.) An MOV is a component that starts to conduct when the voltage across its terminals goes above a certain value. It is used to protect the PSU from voltage spikes. If say you have an MOV rated for 200 Volts DC and it is put across the big 200V caps (which usually see about 170 Volts DC). If all of a sudden there is a surge on the power lines and the voltage goes above 200 Volts on the caps, the MOV will short out and take that voltage surge, thus protecting other components in the PSU. However, an MOV can do this only a few times. If it does it too many times, eventually it shots permanently and usually blows up (and also blows the fuse in your PSU). But, on the plus side, your big electrolytic caps and other components are protected.
So it is good to have it, but definitely not necessary.

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

The X2 cap(square blue color) with label "MKT .22K CIS 280V~X2 GPR 40/85/21/C" is 0.1uF. It reads 0.162uF on capacitor meter.

As you advised, I will keep the extra thermistor and all other coil/inductors as spare. I pulled out the circular blue cap(Y2 safety cap) with label "102 1KV) which I attached picture(Y cap). it reads 1.0 nF on capacitor meter. Can I use on CY103?

I still got one last question on the AVF PSU modding. Today I pulled out the common mode choke with label "YDD-ET24" with good continuity. The four pins on the choke seems a bit narrow to the new pin location as the new pins are wider. Can I also use the same method as the fuse; solder a longer wire on one end and fit inside the new pin hole? Will put on hot glue or electrical tape to prevent shorting other exposed wire.

Hoping for your kind feedback. Your tips and comments are outstanding.
Thanks a lot.

[momaka]

Re: Need help repair dead AVF brand power supply

The X2 cap(square blue color) with label "MKT .22K CIS 280V~X2 GPR 40/85/21/C" is 0.1uF. It reads 0.162uF on capacitor meter.

That's fine.
An X-safety cap with anywhere between 0.47 uF and 0.047 uF will still do an okay job.

I pulled out the circular blue cap(Y2 safety cap) with label "102 1KV) which I attached picture(Y cap). it reads 1.0 nF on capacitor meter. Can I use on CY103?

You can, but I wouldn't advise it.

Reason why is because those blue caps are actually NOT Y2-safety rated. They are just regular ceramic caps. If they were Y2-class, they would have safety agency approvals on them (like CE, TUV, UL, CSA, N, F, D, FI, etc.)

Using non-approved ceramic caps in place of Y caps is somewhat dangerous. Y2-class caps will become open-circuit if they fail, whereas ceramic caps could go open-circuit, short-circuit, or leaky - this can often vary between ceramic caps, even if they are identical. Since Y2-class caps are usually inserted between Live and Ground as well as Neutral and Ground, you run the chance of making the PC's chassis live if you use non-approved Y2 caps (especially if the case it isn't grounded properly). And that is no good, of course.

I still got one last question on the AVF PSU modding. Today I pulled out the common mode choke with label "YDD-ET24" with good continuity. The four pins on the choke seems a bit narrow to the new pin location as the new pins are wider. Can I also use the same method as the fuse; solder a longer wire on one end and fit inside the new pin hole? Will put on hot glue or electrical tape to prevent shorting other exposed wire.

Yes, that should be fine. Alternatively, you can also drill new holes in the PSU's PCB. Either way, just make sure the coil is secured properly. Hot glue will actually work quite well for that.

Keep us posted how the modding goes . I think it would be both interesting as well as educational to people who read this thread and happen to be new to PSU modding. You've done some really good work so far!

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

Great sharing and clear explanation on X safety cap & Y safety cap. It is educational and offer lots of information to those who are modding/upgrade their PSU.

Also awesome tip on soldering longer wire on one end of the common mode choke which I apply to the fuse and resistor(refer image 1073) as well. But I feel my first mod on adding extra 4 wires to the common mode choke doesn't look that neat. However, it works! (refer image 1074) I attached pictures of the final modding front (image 1079) & back (image 1064).

First,after putting in all the components (X cap,choke,thermistor) with 60watt light bulb series in the new fuse location, then put wire to short green wire to ground on ATX connector, I switched on main AC power........the light bulb glows,then shuts off, next the PSU fan spins!

Next, I switched off main AC power, unsolder the light bulb and replaced with the 5A glass fuse. Then, switched on AC main, done voltage testing at ATX connector which at red & black wire(5V rail) DMM reads 5.12, at yellow & black wire(12V rail) DMM reads 11.79 and at orange & black wire(3.3V rail) DMM reads 3.26V.

FYI, it has been a splendid learning journey from a dead ATX slowly being checked part by part with your guidance then transformed to a modified much better PSU of extra inline filter and improved power dissipation.
Due to its limited 250W power (or lower) I will use this PSU as a test bench for small equipment and most likely not used in on computer or sensitive equipment.

Thanks a million for the enormous and superb help.

[fzabkar]

Re: Need help repair dead AVF brand power supply

Kudos to momaka and congratulations to mikey5791. This is how a forum should work.

[momaka]

Re: Need help repair dead AVF brand power supply

Thanks a million for the enormous and superb help.

No problem. Always glad to share knowledge .

The only thing I would add is that you might want to buy some flux (either rosin or RMA). Some of your solder joints look dry and a bit rough. If you put solder on them and re-heat them with your soldering iron again (no solder necessary), they will look nice and shiny like they came from the factory.

But other than that, great work . I hope this PSU serves you well!

Kudos to momaka and congratulations to mikey5791. This is how a forum should work.

Thanks!

Perhaps it should also be taken into consideration that I don't have a job yet, though (still looking ). Thus, I have plenty of time to type detailed posts, since I am sitting at home all day .

[BleedCap]

Re: Need help repair dead AVF brand power supply

FYI, it has been a splendid learning journey from a dead ATX slowly being checked part by part with your guidance then transformed to a modified much better PSU of extra inline filter and improved power dissipation.

Congratulation

Kudos to momaka and congratulations to mikey5791. This is how a forum should work.

I have a question.

As for the 8 coils/inductors you took a picture of: they all have too thin of a wire, so you can't use them in spots L302, L303, or L304. If you want to put inductors in those spots, you can make your own from thick solid copper wire (the same that is used on the big round inductor near the output capacitors).

Can the coil/inductor from motherboard be used?

[momaka]

Re: Need help repair dead AVF brand power supply

I have a question.

Can the coil/inductor from motherboard be used?

The one you have circled in your picture - YES.
It seems good enough for 10-15 Amps, so should be okay to use on any rail in the PSU, as long as you don't intend to use the PSU for a 5V-heavy PC (like a socket 462 or 478 motherboard *without* a 4-pin CPU connector). Most new PCs nowadays use 12V rail, though, so not much to worry.

[momaka]

Re: Need help repair dead AVF brand power supply

To answer your question from this thread:
https://www.badcaps.net/forum/showth...755#post603755

I am eager to find the rating on my AVF brand Model LT-35ATA PSU.

There are four main things that affect the power limit of the PSU: the primary side parts (bridge rectifier, bulk input electrolytic capacitors, primary transistors), the transformer size and PSU switching frequency, the secondary side rectifiers and filters, and the PSU topology (i.e. design).

It's probably easiest and most meaningful to start with the secondary side rectifiers.
You have two FMB-26L and one BYQ28E-200E rectifiers in your AVF PSU. The FMB-26L can handle up to 10 Amps average *per diode*. So in half-bridge topology, that totals to 20 Amps max through each FMB-26L rectifier. The BYQ28E-200E is listed as having a rating of 10 Amps average with *both diodes conducting*, so rating for that rectifier is 10 Amps total. Most likely, your 3.3V and 5V rails each have an FMB-26L, whereas the 12V rail should be with the BYQ28E-200E (since it has a much higher voltage breakdown of 200V). That gives you (3.3 x 20) + (5 x 20) + (12 x 10) = 306 Watts maximum for the secondary side.

The next thing to look at is the size of the main transformer. For a half-bridge design, like your PSU, anything with "33" written on it is generally capable of only 250 Watts max and 300 Watts peak. With a "35"-size transformer, the capacity can go up to 300-350 Watts.

As for the primary side, let's first consider the transistors on the heatsinks. In post #4, you mention your PSU having two E13007 transistors. In general, whenever you see a PSU with 13007 BJTs and the topology is half-bridge, the power limit tends to be 250 Watts continuous, 300 Watts peak (for a short duration of time).

Then there is the bridge rectifier and the (large) input electrolytic caps. In a country with 110/115/120 V AC, the bridge rectifier (or diodes forming the bridge rectifier) will need to have a rating of at least 2.5 Amps to handle 250 Watts continuous and 300 Watts peak. In a country with 220/230/240 V AC, the rating of the bridge rectifier can be half of that for 110/115/120 countries to maintain the same power rating. As for the input electrolytic caps: 2x 330 uF will limit you to about 200 Watts, 2x 470 uF to about 250 Watts, 2x 680 uF to 300-350 Watts, and 2x 820 uF and above for 400+ Watts.

So with all of those power ratings, you really look which one is the lowest one for your PSU and that becomes the limit for it. Since you have only 2x 330 uF input caps and 13007 transistors, I am more inclined to think your PSU can handle probably about 200 Watts at the most, despite the secondary side being capable of much more than that (306 Watts).

[mikey5791]

Re: Need help repair dead AVF brand power supply

Hi momaka,

Great write up and detailed explanation on calculating the actual power rating.
Since the AVF brand PSU can handle probably about 200 Watts at the most, this fact again confirms it can be used for small not critical equipment or for hobby project.

Thanks and have a great day!