Need som info on power supply components

[Pentium4]

Alright, so pretty much since I made my account here I've been trying to learn as much as I an about power supplies. I got a dead Bestec PSU from a buddy a little while ago that had part of the secondary fry, so I've just been desoldering a lot of the components off to see what I can salvage and what does what. So I took off the heatsinks with all the schottky's on them and I want to know which do what.

This heatsink and mosfet came off the primary side of the PSU, it was right next to the Primary capacitors, what does this thing do?


This is a dual 12V rail PSU, so are those schottky's on this side each a 12V rail? What about the small one?


Is this larger one the 5V rail? Don't have any idea what the small one is, bear with me


Not a great picture but here's an overhead shot of it


If someone could please help me explain some of this I would be so happy I'm doing my best to learn as much as I can!!!!

[mariushm]

Re: Need som info on power supply components

http://www.hardwaresecrets.com/article/327

fqa9n90c http://savedonthe.net/download/367/fqa9n90c.html

The main switcher - goes on and off sending pulses through the transformer, the duration being controlled by a smaller chip, depending on feedback coming from the secondary side through those optocouplers (the four small gray things with 4 legs each in the middle)

since this is an older psu, it should be heavy on the 5v do I suspect the two chips in the second picture are shottky diodes, the smaller one or both smaller ones may be 3.3v and one of them is for 12v

But I may be wrong, one of them could be for 5v stand by but then again it's a bestec

[dmill89]

Re: Need som info on power supply components

The FQA9N90C is a MOSFET (a type of switching transistor), Link to Datasheet.

The components on the secondary are schottkey rectifiers.
The STPS3045CWs are rated at 45V 30A each and handle the 5v and 3.3v rails, the STPS20H100CTs are rated at 100V 20A each and handle the 12v rail(s).

All of these are good quality, well rated components that can be salvaged if they test good.

[Pentium4]

Re: Need som info on power supply components

http://www.hardwaresecrets.com/article/327

fqa9n90c http://savedonthe.net/download/367/fqa9n90c.html

The main switcher - goes on and off sending pulses through the transformer, the duration being controlled by a smaller chip, depending on feedback coming from the secondary side through those optocouplers (the four small gray things with 4 legs each in the middle)

since this is an older psu, it should be heavy on the 5v do I suspect the two chips in the second picture are shottky diodes, the smaller one or both smaller ones may be 3.3v and one of them is for 12v

But I may be wrong, one of them could be for 5v stand by but then again it's a bestec

Thanks for the info!

The FQA9N90C is a MOSFET (a type of switching transistor), Link to Datasheet.

The components on the secondary are schottkey rectifiers.
The STPS3045CWs are rated at 45V 30A each and handle the 5v and 3.3v rails, the STPS20H100CTs are rated at 100V 20A each and handle the 12v rail(s).

All of these are good quality, well rated components that can be salvaged if they test good.

Great reply, thanks This Bestec is the beefiest I've seen, but yeah still a Bestec. It's ratings are 5V=25A, 3.3V=25A, 12Va=18A, 12Vb=18A (But sadly only 22A combined) It doesn't look terrible, but it had a 6 pin PCI-E connector and I would NOT want to hook this thing up to a graphics card that needed a 6 pin. The heatsinks don't look too bad either, they're pretty heavy. The bridge rectifier is a GBU606, I also desoldered that. Can you put a bridge rectifier on a PSU that has the 4 diodes? I also desoldered 2 X capacitors, and a PI coil, I could put those on a PSU with no transient filtering right? I was also curious if it's possible to use the transformer in a different PSU. Sorry for all the questions, I'm just really curious and eager to learn this stuff.

[dmill89]

Re: Need som info on power supply components

Can you put a bridge rectifier on a PSU that has the 4 diodes?

Yes, the 4 diodes serve the function of a bridge rectifier, just make sure to get the polarity correct.

I also desoldered 2 X capacitors, and a PI coil, I could put those on a PSU with no transient filtering right?

Yes, just test them to make sure they are still within spec (capacitance test on a multi-meter should do for these).

I was also curious if it's possible to use the transformer in a different PSU. Sorry for all the questions, I'm just really curious and eager to learn this stuff.

Maybe, you can use it in a different PSU as long as it uses the same type of transformer. Some PSUs (especially cheap ones) use different style transformers, some have PCBs silkscreened and drilled for multiple types of transformers and some don't.

[momaka]

Re: Need som info on power supply components

Should have fixed that Bestec rather than part it out. It can be a pretty solid unit with good caps.

I got a dead Bestec PSU from a buddy a little while ago that had part of the secondary fry

The cause was most likely that tan/brown glue - it tends to go conductive over time and can short out components. This is not unique just to Bestec PSUs. IIRC, Enermax and quite a few other manufacturers use it as well. If you ever see it in a power supply, remove as much of it as you can, especially if it has turned brown.
Normally it's tan in color, but with heat and time, it turns brown and conductive.

I was also curious if it's possible to use the transformer in a different PSU

Yes, but the pins for the 5V, 12V, and -12V rails must match. Also, the acceptor PSU must be of the same topology. Read the hardwaresecrets article that mariushm posted in post #2.
FYI, your PSU is a single-transistor, forward-converter topology. *Most* cheap Chinese PSUs are half-bridge topology so you won't be able to use your transformer in one of them.

My advice to you would be to try and fix PSUs first before swapping parts between PSUs and trying to upgrade the cheap ones. This will get you more familiar with PSUs and how they work.

[Pentium4]

Re: Need som info on power supply components

Yes, the 4 diodes serve the function of a bridge rectifier, just make sure to get the polarity correct.



Yes, just test them to make sure they are still within spec (capacitance test on a multi-meter should do for these).



Maybe, you can use it in a different PSU as long as it uses the same type of transformer. Some PSUs (especially cheap ones) use different style transformers, some have PCBs silkscreened and drilled for multiple types of transformers and some don't.

Cool, I wouldn't know how to test it with a multimeter though...I do have one though. How good does the transformer look on this one?

Should have fixed that Bestec rather than part it out. It can be a pretty solid unit with good caps.


The cause was most likely that tan/brown glue - it tends to go conductive over time and can short out components. This is not unique just to Bestec PSUs. IIRC, Enermax and quite a few other manufacturers use it as well. If you ever see it in a power supply, remove as much of it as you can, especially if it has turned brown.
Normally it's tan in color, but with heat and time, it turns brown and conductive.


Yes, but the pins for the 5V, 12V, and -12V rails must match. Also, the acceptor PSU must be of the same topology. Read the hardwaresecrets article that mariushm posted in post #2.
FYI, your PSU is a single-transistor, forward-converter topology. *Most* cheap Chinese PSUs are half-bridge topology so you won't be able to use your transformer in one of them.

My advice to you would be to try and fix PSUs first before swapping parts between PSUs and trying to upgrade the cheap ones. This will get you more familiar with PSUs and how they work.

I feel bad now that I've dissected the hell out of this Bestec but before I cut the wires I figured it was done for. Thanks for the info!! I have a Lepa unit that I think is a single transistor forward but i'd have to check. I do have a decent amount of half bridge PSU's....I still think it'd be cool to upgrade them. I'll post some pics of the Lepa when I get home

[everell]

Re: Need som info on power supply components

Your power supply looks like a Bestec ATX-300 12Z. The motherboard killer Bestecs were the ATX-250 12E. The 12Z series were much better built, and are (in my opinion) much superior to the half bridge economy power supplies made by Deer, L&C, Allied, Solytec, and a host of other unknown brands. The Bestec runs circles around the Powmax and its relatives. Your 12Z has a PWM chip in the 5vsb circuit which will shut down if problems develop rather than destroying the motherboard such as the Bestec 12E and Antec Smart Power units were known to do. The burned looking areas on the Bestecs were in most cases the glue going conductive and turning dark brown or black. Bestec is not the only manufacturer that has this problem. I have found that removing the glue cures the problem in MOST of these Bestecs.

Even if you find a Bestec ATX-250 12E, the motherboard killer, you can gut the 5vsb circuit and replace it with a DM311 PWM chip to resolve the problem permanently. I have a few 12Es that I have modified with the DM311 chip, and all are running fine in some older computers I still play with.

So don't trash a power supply just because it has Bestec on the label. Remove glue, replace any bad caps, and if a 12E mod the 5vsb circuit, and you will end up with a much better power supply than those cheap pos half bridge supplies which deserve the HKFA label.

[Pentium4]

Re: Need som info on power supply components

Your power supply looks like a Bestec ATX-300 12Z. The motherboard killer Bestecs were the ATX-250 12E. The 12Z series were much better built, and are (in my opinion) much superior to the half bridge economy power supplies made by Deer, L&C, Allied, Solytec, and a host of other unknown brands. The Bestec runs circles around the Powmax and its relatives. Your 12Z has a PWM chip in the 5vsb circuit which will shut down if problems develop rather than destroying the motherboard such as the Bestec 12E and Antec Smart Power units were known to do. The burned looking areas on the Bestecs were in most cases the glue going conductive and turning dark brown or black. Bestec is not the only manufacturer that has this problem. I have found that removing the glue cures the problem in MOST of these Bestecs.

Even if you find a Bestec ATX-250 12E, the motherboard killer, you can gut the 5vsb circuit and replace it with a DM311 PWM chip to resolve the problem permanently. I have a few 12Es that I have modified with the DM311 chip, and all are running fine in some older computers I still play with.

So don't trash a power supply just because it has Bestec on the label. Remove glue, replace any bad caps, and if a 12E mod the 5vsb circuit, and you will end up with a much better power supply than those cheap pos half bridge supplies which deserve the HKFA label.

I have another 300W Bestec that I can improve, it's a ATX-300-12Z. I got this one for free and wanted to learn about them so I just started taking it apart. And this one is a ATX-300-12EB3. Maybe I can mod the other Bestec with some of these parts? Because this one looks like they put a little more into it. I find all the hot glue on any PSU's to be extremely annoying!

[everell]

Re: Need som info on power supply components

I have another 300W Bestec that I can improve, it's a ATX-300-12Z. I got this one for free and wanted to learn about them so I just started taking it apart. And this one is a ATX-300-12EB3. Maybe I can mod the other Bestec with some of these parts? Because this one looks like they put a little more into it. I find all the hot glue on any PSU's to be extremely annoying!

The Bestec ATX-300-12EB3 is a more current version of the Bestec line. It has two 12 volt 18 amp overcurrent protected rails. Very good for newer design computers which are more heavy on the 12 volts. A good one to fix and use. Does it work at all?

A common problem on this power supply is bulging (or bad) capacitor at location C36 due to heat. It is located next to the heat sink and probably doesn't get much air circulation. Check your power supply for bulging cap at C36.

[mockingbird]

Re: Need som info on power supply components

Your 12Z has a PWM chip in the 5vsb circuit

I have an ATX-300-12Z Revision "CDR". I looked for the +5VSB IC, I found two chips.

One is the A6351 and the other is an ST UC3842B. Usually when I check the datasheets for these 8 pin ICs, one of them turns out to be for the standby but both these seem to be voltage comparators. Is this correct?

Regarding the cap C36 near the diode that gets very hot. I've looked at an image you uploaded in a previous thread where you showed where to move it to, I can't find a suitable place to move it to in my revision, as it's different than yours.

[everell]

Re: Need som info on power supply components

The A6351 chip is the 5vsb chip. To move C36 to the other side of the heat sink, here are pictures showing where to drill holes in the new location I used.

[mockingbird]

Re: Need som info on power supply components

Everell - Thank you, I have found a good place to put it. Do you know what the actual voltage for this cap is? I have a 16V 2200uF 10mm OST cap there. I am correct in assuming that this is for the 5VSB circuit and that a 6.3V would suffice here?

I took out most of the glue. There must be some Chinaman at the Bestec factory with the glue dispenser obsessed over getting it into every nook and cranny.

[everell]

Re: Need som info on power supply components

The capacitor for this location is 2200 uF/10 volts, a 6.3 volt will probably do but I prefer using a 10 volt cap. A 12 mm diameter cap should fit in either the original position or in the new position where I drilled new holes.

I think someone at the Bestec factory thinks he or she is decorating a cake when they get the glue gun in hand. Some of the glue jobs looks very "creative".

Am I correct that what you have is a Bestec ATX-300 12Z? Bestec has several very similar models.

[everell]

Re: Need som info on power supply components

Here is the correct data sheet for the 5vsb chip

[mockingbird]

Re: Need som info on power supply components

I've got a 16V 2200uF OST "RLS" series cap there (And it's not bloated. All the rest of the caps on the PSU are, this is one of the only ones that isn't). Thanks for the datasheet, I looked at that yesterday and I didn't see anything there about using it in a standby circuit like I usually see with 5VSB datasheets, that's why I asked.

Ok, I'll probably end up measuring it. Reason I'd prefer a 6.3V cap there is because I can get them for pennies on the dollar.

Yes, I;m sure it's a 300-12Z, revision "CDR". I think it's an early model, vintage 2005.

Have you seen the Q110 chip in a PSU before for 5VSB? I found one in a Lite-ON yesterday. What do you think about it?

[everell]

Re: Need som info on power supply components

Have you seen the Q110 chip in a PSU before for 5VSB? I found one in a Lite-ON yesterday. What do you think about it?

Have NOT seen one. Rather than hijack this thread, I think we should leave it as a Bestec discussion. Start a new thread on the Lite-On. Be sure to include the model number and some pictures. Also include a data sheet on the Q110 chip if you have one.

Did you get your Bestec ATX-300 12Z working?

[mockingbird]

Re: Need som info on power supply components

I just practiced drilling a hole on an unneeded PCB, the size is perfect, so I'm going to attempt it on the 300-12Z.

No, I still have to order caps for this thing, just taking care of all the preliminary stuff first.

[mockingbird]

Re: Need som info on power supply components

Ah,

One thing I forgot to ask you... In a different thread, you mentioned a mod to tweak the 12v and 5v voltage with a trimpot. I looked up that model, it's $5+ at Digikey. Do you remember which value gave you optimal voltages so I can just swap the resistor?

I'm almost done removing and cataloging the caps. I drilled the two holes, almost as nice and clean as the ones you made, could have been better if I could only find that set of dremel bits I have lying around somewhere.

[everell]

Re: Need som info on power supply components

1. The resistor value will vary from one power supply to another. That is why I did the modification to replace that resistor with a 50K pot. Using fixed resistors is a hit/miss situation.

2. The value needed will vary from one mother board to another. If you want to tweak the output voltages for a specific power supply mated to a specific mother board, the pot is the way to go. Do the mod, fire up the psu, and adjust the pot to set the voltages for what you want. Then you are done! No more hassle.

Also.....if you like to tweak.......add a 5vsb fan circuit such that when power supply is off but plugged into wall outlet, the 5vsb fan comes on and keeps everything nice and cool. Then when you turn the computer on, the 5vsb fan goes off and the main fan comes on.