Bestec revisited

[everell]

I have seen much posted on this website that Bestec is nothing but poorly designed mobo killer. Most of the problem has been attributed to 5VSB poorly designed. I have repaired two Bestec model ATX-250 12E psu that did indeed have poor 5VSB flaw. The pc board was discolored from overheating and components failed which allowed the voltage to go well above the 5 volt level.

On the other hand I have repaired two Bestec model ATX-250 12Z which have a 8 pin pwm chip (A6351A) for the heart of the 5VSB circuit. The 5VSB did NOT fail in either of these two PSU, and the pc board was not discolored from overheating on these two PSU. Perhaps the engineers have admitted the need to redesign - and the later model does indeed seem to have a much improved 5VSB.

Bad capacitors can still be a problem, but that is a problem on lots of PSU. Perhaps it is time to elevate the later better designed Bestecs to a higher level of quality, especially above PowMax (aka maximum bang). I'll post some photos of one of these later models, along with a drawing of this new chip design 5VSB.

[Wizard]

Re: Bestec revisited

Much better.

This tend to not fire up if cap is bad in that area especially this IC design is done right.

Cheers, Wizard

[i4004]

Re: Bestec revisited

>On the other hand I have repaired two Bestec model ATX-250 12Z

what was wrong with those, and what's the price for that model?

[everell]

Re: Bestec revisited

But ...... Did the two ATX-250 Rev Z units that failed for you have the pwm chip in the 5VSB circuit (I don't trust labeling) AND if so did the 5VSB circuit fail? My concern is the 5VSB failing causing burn damage to the PSU and causing damage (or killing) the mobo.

Of the two that failed for me, one had a resistor value change that simply shut the power supply down. The other had a shorted switcher which took out the fuse.

I don't doubt that this is an economy (bargain basement) class of PSU. But I do think this later model is much safer, less of a fire hazzard, and less likely a mobo killer. It also has more capacitor filtering on the outputs than the infamous POWMAX.

[i4004]

Re: Bestec revisited

who were you replying to in that post?
some pm?

anyway, thanks for the answer.....

[Toasty]

Re: Bestec revisited

>>who were you replying to in that post?<<

You, I'm sure. He thought you made the "On the other hand I have..." statement, not realizing you were quoting him.

Anyway, Bestec's name has been so thoroughly trashed, it would be tantamount to naming your child Adolf. No one will forget...


Had a Compaq system come in yesterday with problems running programs and strange happenings at boot. Opened the cover to dust it out, and there was a Bestec ATX-250-12Z. Pulled it and put in a new el-cheapo ($29) supply and the system runs fine. Told them, when they have the money to come back and I'll swap it for a better unit.

[Toasty]

Re: Bestec revisited

Here Everell-

Datasheet IR IRIS-A6351

----------------
Edit: Sheet won't attach. Says too big. brb

[Toasty]

Re: Bestec revisited

Again-

Datasheet IR IRIS-A6351



Shrunk original by 120kb

[everell]

Re: Bestec revisited

To i4004 I would like to apologize if I have offended you in any way. Your posts are interesting and informative, and you experience and expertise is GREATLY appreciated.

To Toasty I would like to say that your latest Bestec failure sounds very predictable for what I was saying. If The PSU has the IC for 5VSB circuit, then it protected the mobo such that you were able to simply replace the PSU and get computer back into operation. It would be interesting if you would open it and look for:
1. Does 5VSB use IC or two transistor design?
2. Is there any pc board discoloration from heat in the 5VSB circuit?
3. If not a 5VSB failure - is it just another capacitor failure? Do you have one of those Bob Parker Blue ESR meters? I just got one and am excited about all the new things I am finding out about.

Since this is a website for PSU design and troubleshooting, I hope I am not being offensive in asking such questions and hoping for more discussion.

[Wizard]

Re: Bestec revisited

Bestec traditionally used transistors/discrete components for 5Vsb which tend to run hot, bad capacitors, blow up or overvolt and destroy mainboards.

But when they started using intelligent designed 5Vsb using IC that has shortcircuit, overvoltage protections built into the IC. And tend to run cooler, more reliable. If the capacitor go bad, this type of IC tend to shut down and play safe.

Cheers, Wizard

[i4004]

Re: Bestec revisited

>not realizing you were quoting him.

heh, yes...still gotta wonder how come those words of a "stranger" didn't sound surprisingly familiar...just like echo...


>To i4004 I would like to apologize if I have offended you in any way.

no reason to apologize, i was just confused by your 1st paragraph which seemed to came out of nowhere...but ok, now you know i use '>' to quote....
as i'm too lazy to use full form reply(i use quick reply 99% of the time)
also, i usually only use lower case, so that's another way to distinuguish...

>I hope I am not being offensive in asking such questions and hoping for more discussion.

no, surely not...it was just a small misunderstanding....
when i asked who were you replying to, i didn't mean anything condescending(even if it may look that way). i was just asking because i didn't see origin of that 1st paragraph...that was all...
to that extent i should apologize to you, if it came somewhat ambiguous..
so i apologize if it sounded harsh...that wasn't my intention...


yes, discussions about psu failure modes are very interesting...in the end they tell us what psus are safe to use, and which are not...and that it VERY important
-----------------
> put in a new el-cheapo ($29) supply

which one?

[Toasty]

Re: Bestec revisited

i4004 >>which one?<<

I think it was WhoFlungDung brand.

Weighed about 1/2 of what the Bestec does. Ratings say 400watt... ROFLMAO yeah, right.

[Toasty]

Re: Bestec revisited

>>1. Does 5VSB use IC or two transistor design?<<

?? I have not investigated but am assuming it's the IC type. It's identical to yours except it's dated 0344 and has less goop and 2 bulged caps. Same WAN NIEN 101V0A markings.

>>2. Is there any pc board discoloration from heat in the 5VSB circuit?<<

Board is excellent, "factory fresh".

>>3. If not a 5VSB failure - is it just another capacitor failure? Do you have one of those Bob Parker Blue ESR meters? I just got one and am excited about all the new things I am finding out about.<<

Yes - 2 obvious ones: 1 bulge, 1 bulge & leak - 2200uF/10v Jamicon's

Yes

Yup, it's fun. Just wish I didn't have to zero it EVERY TIME. :\ Instructions had some errors too, but I pushed through them. Novice builder would be lost or asking questions. (Resistor codes wrong and regulator(?) IC wrong #)

[370forlife]

Re: Bestec revisited

I don't think bestec's newer power supplies are too terrible except for the bad 5vsb thing that goes on with them. I have a 300w version that has a actual AC rectifier, Panisonic primary caps, CapXon secondaries, decent heatsinks and a good cfm fan.

...I still don't trust it.

[Toasty]

Re: Bestec revisited

370forlife >>...I still don't trust it.<<

Like I said earlier, it's the name that kills it because you KNOW it's history. It wouldn't matter if the case was platinum plated, it weighed 3 pounds, had 3 fans, and the caps were all Panny's, it still says Bestec.

Run Away! Run Away!

[everell]

Re: Bestec revisited

Toasty - I have never heard of WhoFlungDung brand. Is this a joke or are you serious?

Just for fun, lets compare this Bestec ATX-250 12Z with a REAL mobo killer - a 350 watt PowMax that I ran for 6 years with no trouble, but didn't realize what I had.

Looking at the photo of the Bestec, you can see that it has two nice size toroid coils and several filter caps on the AC line input. The bridge rectifier is one piece, and a respectable size. Two filter caps 470 uF @ 200V. It uses a pwm chip UC3842, and TPS3510 supervisory chip. It has four feedback optocouplers, one of which is to protect the 5VSB circuit which uses the A6351A pwm chip. It has two toroid filter coils on the output.

Now look closely at the photo of the PowMax which fortunately didn't crap out. On the line input one much smaller torroid line filter. Look at the bridge diodes - four seperate diodes - of three distinctly separate physical sizes. The two filter caps are 330 uF @ 200 V. The pwm switch is the old AP494, no supervisory chip, the 5VSB circuit is just a couple of transistors, and NO feedback optocouplers. The main switching transformer is about half the size of the one in the Bestec. It has only one toroid filter coil on the output. The only redeeming thing I found is a 7805 regulator chip for protection of the 5VSB.

Thanks to finding this website and looking over the many posts and experience you guys (and gals?) have, I immediately pulled the PowMax out of service. Haven't decided yet on its replacement, but no more PowMax!

I don't mean to say the Bestec is highest quality - but for the "cheaper" PSU, it does look to me like it is far superior to the PowMax.

[Toasty]

Re: Bestec revisited

everell >>Is this a joke or are you serious?<<
Dead serious. >:| >:| >:|

Made by HongKongFlyApart Company, LLC.



ROFLMAO

[Toasty]

Re: Bestec revisited

370forlife >>I don't think bestec's newer power supplies are too terrible except for the bad 5vsb thing that goes on with them.<<
I don't think the newer ones, such as the 12Z discussed here, are going to have this issue. Everell has substantiated that they have improved their design. It seems that they learned of the destruction they were causing and built more robust and better protected units.

Everell's confirmation of the protection makes it more likely that a re-cap of (now)my unit might be in order just to get rid of the crap caps.

Few of us would know any better if not for these forums. We'd simply look at the failure as an "oh well", and go get a new PSU. Or, would waste a lot of time chasing a software issue that did not exist.

@Everell
It seems that the PowMax and Bestec units are related to the same designer/builder, Wan Nien.

Cheers!
Toast

[jpdoe]

Re: Bestec revisited

I remember reading somewhere that Wan Nien is a PCB manufacturer.
If so, it's not the PSU maker, but a part provider.

http://www.ettimes.net/theme/etv2.asp?memberid=49650297

[i4004]

Re: Bestec revisited

powmax rocks hard!
everything that's connected to it...hehe...