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**PCBONEZ** · 03-19-2009, 07:47 PM

Re: Bestec ATX250-12E up and running!

Except for this one: "1000 uF 10 V .06"
.. they are about right for PSU caps.
Even that one isn't broke yet, just on it's way probably.

**MiG** · 05-14-2009, 08:32 AM

Re: Bestec ATX250-12E up and running!

Everybody who claims CEC to be a crap brand is rather stupid. OK, some get bulged bit not more often then Chemicon or Fujitsu. Enermax (Galaxy, Infinity, FMA...series), good SuperFlower PSUs and some mediocre Xilence use JPCE models of electrolytes. The quality is equal to TEAPO and Samxon, not the best but certanly good enough, with small faliure statistics!

**PCBONEZ** · 05-14-2009, 03:58 PM

Re: Bestec ATX250-12E up and running!

Interesting that I block i4004 and you show back up a few hours later,,,, i4004.

You have a right to that opinion and if you look real hard out of the 11,536 members here you might find 10 or so that agree with you.
-
You basically just called 1,000's of people stupid.
- Just here to start an argument again,,,, i4004?

My opinion [which is consistent with the most experienced people here] is that CEC [JPCE-xxx] is:
A crap brand marginally better than Fughyyu.
Absolutely not up to Samxon quality.
Not quite on a par with Teapo in PSU's, more like OST.

You go ahead and seek them out and use them.
I will continue replacing them.

PCBONEZ - Member, i4004 on Ignore Club.

.

**370forlife** · 05-14-2009, 04:31 PM

Re: Bestec ATX250-12E up and running!

JPCE are certainly not the worse out there, but they are bad.

I have seen some newer psu's with them vented in them, and I have seen some p3 era enlight psu's with them still running just fine.

**i4004** · 05-17-2009, 06:18 PM

Re: Bestec ATX250-12E up and running!

>My opinion [which is consistent with the most experienced people here] is that CEC [JPCE-xxx] is:
A crap brand marginally better than Fughyyu.
Absolutely not up to Samxon quality.
Not quite on a par with Teapo in PSU's, more like OST.

i did well in persuading pcbonez there are more than 2 grades of quality.
<wink>
he mentions no less than 4 grades above....yiiihhhhaaaaa!

---------------------

>I interpret these readings as reasonably good. Therefore the heart of the problem with this PSU was the bad 5VSB circuit, including the one bad bulging capacitor which was trashed many days ago.

yes, it's the 5vstby circuit: badcaps on the output can't blow the mobo.
as linuxguru condensed it nicely:
Actually, the two transistor +5Vsb circuits (either BJT or MOS switch) are reliable - but one electrolytic (usually 22uF/50v or 47uF/50v) used on the primary side of the flyback is critical. It eventually dries out, causing an auxiliary secondary-side over-voltage on both the controller power rail, as well as +5Vsb. If it doesn't take out the mobo first, it will take out the PWM controller circuitry and then the mobo.

the silliest thing is this: i've found 5vstby circuit (in cheap chinese crap psu) that doesn't have any lytics in primary of 5vstby circuit.
so they could of build better circuit with less components(cheaper) if they knew what they were doing.
see attachments.
notice bulging caps everywhere, even on 5vstby secondary...this psu is still working.
"brand" of this one is "maxpower".

Attached Files

**martp** · 12-24-2009, 04:28 PM

Re: Bestec ATX250-12E up and running!

I had the same problem with my ATX-250-12E, +5VSB was to high. Thanks to your schematics and alot of testing, i found the prbblem it was C1 (10 uF/50V JAMICON connected to pin4 of photo-coupler PC2). I replaced it, and my +5VSB is within 1% of 5V. Thank you.

Martin Proulx

**everell** · 12-24-2009, 07:48 PM

Re: Bestec ATX250-12E up and running!

Hi Martin - welcome to the forum. I see that your post concerns the Bestec ATX-250 12E. How ironic.......this was my first post, concerning the same model power supply. I stirred up lots of comments ...... I didn't realize that most folks hate the Bestec brand power supplies. After much discussion, we narrowed the problem down to one model in particular, the Bestec ATX-250 12E.

Glad to have been of help with my schematics. At the time I worked on mine, it had extensive damage to several components. That's why I gutted the 5vsb circuit and made the add on board. The existing 5vsb circuit will ALWAYS be subject to problems with capacitor C1 failure, which shortly afterwards takes out C50 and dominoes to take out other parts as it self destructs. The more I looked at other power supplies with the two transistor 5vsb circuit, nearly all of them have that critical capacitor, and many other brands have been known to go overvoltage. But the Bestec ATX-250 12E has a unique 5vsb circuit which can put on exciting fireworks - taking out both power supply and mother board.

If you decide to do some experimenting with this power supply, search this forum.....I started several threads with additional changes and ideas for this particular model. Glad that you got yours working, and I hope to see more posts from you.

**goodpsusearch** · 12-24-2009, 08:44 PM

Re: Bestec ATX250-12E up and running!

But for those who don't know much of electronics or those who don't want to spend much time modding, replacing the critical 5vsb 50V capacitor and 5vsb output caps with high quality low esr ones isn't a quite nice way to have a relatively safe psu?

**everell** · 12-24-2009, 09:18 PM

Re: Bestec ATX250-12E up and running!

Excellent question.

First, and most important - SAFETY. Personal safety. All of these power supplies have dangerous voltages when operating. That's why they are in a metal box. For those trained in working electrical equipment and electronics, they are great to experiment with. Carefully, and with the greatest respect for the dangers of electricity.

Secondly, Bestec ATX250-12E has a known design flaw in the 5vsb circuit - well documented in this forum. Replacing the critical capacitors, C1 and C50, and replacing the output 5vsb capacitors, C36 and C37, will in most cases get this psu operational again. This too has been documented by several members. But even with these repairs, C1 can again fail with more aging, and blow up, taking the mother board with it. Also documented on this forum. Therefore, this model psu - without modification - is like a time bomb. In my opinion, it should NOT be used even after replacing C1.

And third - for those of us who like to experiment - it can be modified and made into a very dependable power supply. But - if you don't have electronics training and background, or if you don't feel comfortable working with the high voltages in a computer power supply - then don't attempt modifications. Just put it in the dumpster OR sell it on Ebay!

Kerri Jane had a excellent post reminding us of the liabilities of modifying power supplies. If you do a good job, you can make the power supply better, safer, and more reliable. If you goof, the liability is yours. That includes damage to the power supply, damage to your computer, fire, explosion, burning your house down, etc. On the other hand, this section of the forum is entitled "Power supply design and troubleshooting". I think this is the right place for those who want to experiment. I hope some of the other members who have experiences with the Bestec ATX250-12E will give an opinion.

**ratdude747** · 12-24-2009, 10:08 PM

Re: Bestec ATX250-12E up and running!

idea: on the bad +5vsb circuit, why not poly mod that? just a thought.

**everell** · 12-24-2009, 10:54 PM

Re: Bestec ATX250-12E up and running!

Good evening, Ratdude. You have misunderstood what I am trying to say. The original circuit works great as long as the critical capacitor is good. But IF the capacitor goes bad, the circuit design is bad, and results in the "Bestec" overvolt problem. Notice that I didn't say what type of capacitor was used, but rather that any type MUST be good for the circuit to work properly. Using a better and more reliable capacitor does NOT mean that the capacitor will never fail. It only reduces the chance of failure. What I am saying is that the DESIGN of the circuit is bad - because ANY type capacitor used that goes bad will cause the overvolt - "boom" - problem. So using a poly type capacitor might REDUCE the risk, it will not assure no failure. The bottom line is that the design of this two transistor 5vsb circuit causes more serious damage when failing than other designs of the two transistor 5vsb circuit.

**i4004** · 12-25-2009, 12:23 AM

Re: Bestec ATX250-12E up and running!

actually rat's idea is not a bad one, given that polys tolerate heat better than normal lytics, but that still doesn't change the facts everell mentions.
even with poly there it's still nowhere near his dm311 mod.

>But for those who don't know much of electronics or those who don't want to spend much time modding, replacing the critical 5vsb 50V capacitor and 5vsb output caps with high quality low esr ones isn't a quite nice way to have a relatively safe psu?

i would say either get the psu with dm311(or topswitch) on +5vstby primary(or at least +5vstby design without lytics on primary side), or mod it like everell.

and the mod itself is not hard even for rookies, you can see it uses only few passive components alongside the dm311, and everell shows you how to connect everything.

it's really excellent stuff, and kinda makes me a bit sad that this didn't happen back in the 2001 when cheapo psu destroyed my pc...as usual, one only takes notice AFTER something goes "boom"...heh
but we've definitely learned from the past when it comes to such issues, and people visiting here will profit from that.

**ratdude747** · 12-25-2009, 07:53 AM

Re: Bestec ATX250-12E up and running!

i know that the custom circuit is better. i was just saying that if your parts are limited, then a poly beats a lytic.

**everell** · 12-25-2009, 03:00 PM

Re: Bestec ATX250-12E up and running!

The poly capacitor would probably work OK and last longer. Good idea from that standpoint. But if you are unfortunate enough to have a repaired Bestec take out your motherboard, its enough to make a grown man cry!

I now have a second Bestec ATX250-12E Its 5vsb was still functioning OK. Took some photos of it to show beginning of heat damage - but not as bad as when they actually fail.

Attached Files

**delaware74b** · 12-25-2009, 03:04 PM

Re: Bestec ATX250-12E up and running!

If the 2-transistor +5VSB and Bestec ATX250-E's are such a problem, wouldn't a simple mod of adding a 5.3-5.5 volt zener diode across the output and ground as well as adding a 2-amp fuse do a better job of protecting a mobo in case of cap failures. I'd put the fuse in series before the zener diode so it blows the fuse and opens the +5VSB when the diode begins to conduct to ground. Any thoughts on this?

**everell** · 12-25-2009, 03:29 PM

Re: Bestec ATX250-12E up and running!

I worked on a Fortron FSP200-60ATV which had two transistor 5vsb circuit and zener across the 5vsb output. I don't know the sequence of events of the failure, but it most likely went overvoltage. The zener began conducting current until it exceeded its max limit and shorted. The two transistor 5vsb circuit continued pouring out more energy which went thru the 5vsb diode rectifier, thru the shorted zener, and to ground, This caused the burn damage circled in the photo. The burn area went all the way thru the pc board making it useless for repair. This problem continued until it blew the fuse.

The solution is to use pwm type chip which detects overvoltage and overcurrent problems and shuts down.

Attached Files

**i4004** · 12-25-2009, 03:57 PM

Re: Bestec ATX250-12E up and running!

just found this gem: one (power) transistor and no feedback circuit at all.

luckilly it didn't cause mobo damage.

Attached Files

**i4004** · 12-25-2009, 04:01 PM

Re: Bestec ATX250-12E up and running!

and one more: this one has 2 trans. design, and no lytics in the 5vstby circuit...
but eventually badcaps on other places (secondary) make it a non working psu....

also no damage to mobo.

Attached Files

**everell** · 12-27-2009, 10:23 AM

Re: Bestec ATX250-12E up and running!

Back to the Bestec ATX250-12E

I removed the heat sink with the two switching transistors and capacitors C1 and C50.

C1 = Jamicon 10 uF/50 volts esr > 99
C50 = CapXon 220 uf/25 volts esr = .92

This 5vsb circuit was well on the way to failure, but had not yet blown up, or gone very far overvoltage. Here are photos showing the burn damage from each of the six components that results from C1 failing.

Attached Files