ATX CoolMax CX 400B Blown Capacitor

[SevillianSTS]

I have a CoolMax Model: CX 400B ATX Power Supply

It has a blown capacitor. I am assuming it is filtering the raw power coming into the unit.

Trying to figure out what to replace the capacitor with; it is totaly burnt so I can not read the side of it. Is there a general size you would recommend, or does anyone have access to a schematic ?



The circuit board says LYP004A and Rev 1.6

[cheapie]

Re: ATX CoolMax CX 400B Blown Capacitor

That's an NTC thermistor (note the "TH1" marking), but I don't know about any replacement suggestions. Something may have been shorted on the primary side causing that to blow.

[PeteS in CA]

Re: ATX CoolMax CX 400B Blown Capacitor

Like fuses, inrush limiting thermistors don't usually blow without reason. Chances are one or both of the switch devices has shorted. The heatsinks look pretty substantial, adequate for 400W. Maybe with re-capping the output caps (I assume they are not the best quality), replacing the thermistor and switch devices might yield a very decent P/S. Check the fan(s) to see if it (they) is/are healthy.

[Agent24]

Re: ATX CoolMax CX 400B Blown Capacitor

Couldn't the thermistor be taken out by a surge etc too?

[Pentium4]

Re: ATX CoolMax CX 400B Blown Capacitor

Decent PSU, I'd recap it. A better rated NTC thermistor wouldn't hurt. Did the fuse blow too?

[SevillianSTS]

Re: ATX CoolMax CX 400B Blown Capacitor

Fuse is good.

[SevillianSTS]

Re: ATX CoolMax CX 400B Blown Capacitor

When you says "switch devices" are you referring to the mosfets under the heat sinks ?

I can get a new one of these for $34; is this still worth the work ?

[Pentium4]

Re: ATX CoolMax CX 400B Blown Capacitor

When you says "switch devices" are you referring to the mosfets under the heat sinks ?

Yes. Although they are most likely Bipolar transistors, probably 13009's. It's worth fixing if you want to learn

[PeteS in CA]

Re: ATX CoolMax CX 400B Blown Capacitor

When you says "switch devices" are you referring to the mosfets under the heat sinks ?

I can get a new one of these for $34; is this still worth the work ?

Some P/Ss use MOSFETs, some use bipolar junction transistors (BJTs). So I cover both possibilities by saying "switch devices". Judging by the core material used for the O/P inductors and what I know of common design practice, that P/S probably has BJTs, probably switches at ~25-30KHz, and is probably controlled by a TL494 or TL494 clone. P4 probably recognized what I did, and I agree with his last sentence. If $$ is your only criterion, buying a new P/S would be cheaper in $$ plus your time. But at that price you'll probably be getting a P/S not capable of its full rated power and a decent lifetime, and some/all of the O/P caps will be @#$% with limited life even at 40%-60% of rated power.

Fixing the P/S would probably be more expensive, and cost several hours of your time. Is learning more about P/Ss of value to you? If your answer is, "No," that doesn't make you an idiot, just some one won't be earning part or all of your living in electronics repair (or who does specialized repair). Power electronics has been my career for over 3 decades; OTOH, most of what the computer geekasoids here on BC talk about is Urdu to me.

[Th3_uN1Qu3]

Re: ATX CoolMax CX 400B Blown Capacitor

You can see the controller in the first pic, it's a SG6105D which is a TL494 + two TL431 + some protection circuitry in the same package. And yes, it's gonna have 13009 switching BJTs most likely. Be aware they also like to take some of the driving circuitry with them when they blow. The 1N4148 (glass package) diodes and small capacitors next to them should also be checked if you find one of the power transistors short.

[larrymoencurly]

Re: ATX CoolMax CX 400B Blown Capacitor

Datasheet for the SG6105 controller chip and application note with example schematic:

[senz_90]

Re: ATX CoolMax CX 400B Blown Capacitor

Hey, that's a good PSU with decent heatsink.

I think your problem didn't too complicated, sure it is worth to fix it and learn about it.

Ship to me if you don't really want to learn it and wanna throwing it on garbage

[PeteS in CA]

Re: ATX CoolMax CX 400B Blown Capacitor

You can see the controller in the first pic, it's a SG6105D which is a TL494 + two TL431 + some protection circuitry in the same package. And yes, it's gonna have 13009 switching BJTs most likely. Be aware they also like to take some of the driving circuitry with them when they blow. The 1N4148 (glass package) diodes and small capacitors next to them should also be checked if you find one of the power transistors short.

Yeah, when a BJT shorts C-B that applies 150V-300V to the B-E and to base drive components designed for 10V-30V circuit voltages. And if a high current pulse from something shorting goes through the base drive transformer, that can get fed back to the PWM. All in all, not pleasant.

When I was at Delta products 13 years ago they had a couple of ASICs: one integrated one or more references and several comparators to do supervisory functions; another combined a 3854-style PFC controller and 384x-style PWM into one package. Delta used 384x type PWMs, which operate on the primary side, while TL494-type PWMs are typically used on the secondary side. So Delta didn't combine PWM and supervisory functions the way the SG6105 does.

[LLLlllou]

Re: ATX CoolMax CX 400B Blown Capacitor

OTOH, most of what the computer geekasoids here on BC talk about is Urdu to me.

What a coincidence, I just replaced the Urdu in my laptop!

[TELVM]

Re: ATX CoolMax CX 400B Blown Capacitor

I've observed that some PSUs have the inrush NTC thermistor jacketed with heat-shrink tubing:


Apart from limiting shrapnel proliferation if the thermistor blows up, does the jacket have any other advantages/drawbacks for thermistors?

[SevillianSTS]

Re: ATX CoolMax CX 400B Blown Capacitor

This power supply came out of a Core2Duo computer that I may be turning into a server.
I read that this power supply is 70% efficient. I found a newer 80% efficiency power supply for $35
Being the server would be pretty much running all the time, would you recommend going with the newer 80% or just stick to this one.

Also, what are your thoughts on whether or not this power supply took out the motherboard with it ?

If I am going to fix this one, what would be the first line of attach ?
Remove the heatsinks and test the BJT's What is the procedure to test the BJT's

Thanks again. =)

[Pentium4]

Re: ATX CoolMax CX 400B Blown Capacitor

This power supply came out of a Core2Duo computer that I may be turning into a server.
I read that this power supply is 70% efficient.

Usually when they say "70% efficient" that normally means worst case scenario. Realistically, it will probably be in the 74-78% range, especially with the lower loads.

I found a newer 80% efficiency power supply for $35

Can you post a link of the $35 PSU you are looking at? Some cheap PSU's have fake 80+ ratings.

Also, what are your thoughts on whether or not this power supply took out the motherboard with it ?

I think your motherboard will be okay as it looks like all the damage was done to the primary side of the PSU and not the secondary.

If I am going to fix this one, what would be the first line of attach ?
Remove the heatsinks and test the BJT's What is the procedure to test the BJT's

Yes, you will get better results testing them out of circuit. Do you have a multimeter? Do the following and post your results:
Set your multimeter to diode check mode:
Red probe on pin 1, black probe on pin 2
Red probe on pin 1, black probe on pin 3

[Agent24]

Re: ATX CoolMax CX 400B Blown Capacitor

Yes, you will get better results testing them out of circuit. Do you have a multimeter? Do the following and post your results:
Set your multimeter to diode check mode:
Red probe on pin 1, black probe on pin 2
Red probe on pin 1, black probe on pin 3

In addition, you may find this useful, which describes the process in more detail: http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

[SevillianSTS]

Re: ATX CoolMax CX 400B Blown Capacitor

http://www.newegg.com/Product/Produc...82E16817256060
so it's on sale for 39

and yes I have a MM and pretty competent with a soldering iron, just new to some of these components.

[SevillianSTS]

Re: ATX CoolMax CX 400B Blown Capacitor

any thoughts on that power supply in my previous post ?