Cheap PSU: Piece of junk or semi-decent?

[tom66]

Re: Cheap PSU: Piece of junk or semi-decent?

Trust me, I worked at a company manufacturing electronics. Everything we designed that was sold in EU had to be CE tested. There was a degree of self-certification - for example, we were allowed to change the wiring looms on individual items or make board level repairs if we were confident it wouldn't affect the certification - but the overall system design and construction had to be fully tested in an EMC chamber for both conducted and radiated emissions over the full specification. You can sell a few products without CE, but you will quickly get in trouble.

Importers know that they can't risk the items being pulled and seized so they make sure the proper documentation exists before reselling it.

There's a new CE subsection coming into law that will make it easier for individuals or small businesses to self-certify: by design, or comparison to similar products. But I believe there's a revenue or item limit - can't recall exactly what the standard is and I think it's still on the drawing board.

[Per Hansson]

Re: Cheap PSU: Piece of junk or semi-decent?

tom66: Yea sure but it's very different with a PSU designed in the UK vs one designed & built in China
They don't give a fuck about the CE rating, they just draw up a nice CE logo and sell the crap, just look at the links I provided, all those PSU's where CE marked

[Th3_uN1Qu3]

Re: Cheap PSU: Piece of junk or semi-decent?

designed & built in China
They don't give a fuck about the CE rating, they just draw up a nice CE logo and sell the crap, just look at the links I provided, all those PSU's where CE marked

I can confirm that.

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

As an addendum, I've just tried my first ever PSU modding.

Had a cheap P4 era PSU, typical gutless wonder with the four-diode treatment and empty real state in the PCB with markings for absent ferrite coils, Y-caps and X-caps. This one volunteered for the sacrifice in the name of scientific learning .

Had another 1998-vintage ATX PSU ( in 2002) resting in the attic under tons of dust . This one donated its organs (KBL 406G bridge recitifer, ferrites and X/Y-caps).

After some decyphering and head scratching I thought I trusted how to correctly solder the bridge recifier's four legs to the PCB. I was very worried about the X/Y caps lacking polarity marks ... until I discovered that X and Y caps lack polarity ('logical, as they eat AC, you moron' ).

A couple hours and a ton of harsh language later the soldering was done.

Then I got my best armour, called the firemen and NATO to be on stand-by, clipped green on black, and plugged my creation to the wall .

To my astonishment, no explosion and no smoke , the PSU fan just turning OK .

Plugged and old, expendable fan to a molex: Turning OK .

Measured +12V and it was ~12V. So on with ~5V and ~3.3V . Amazing!


Still lack the courage to plug it to any valuable comp, however .

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

Go on, swap switching transistors I bet there are 13007 now? Try 13009 or something fatter (2SC2526 are common too).

[PeteS in CA]

Re: Cheap PSU: Piece of junk or semi-decent?

(MJE)13007s are 70s-designed parts that were/are really good at what they do, too good to totally die out (78xx and 79xx 3-terminal regulators, TL494 PWMs, LM339 quad comparators and LM324 quad op-amps are of similar or older vintage). The (MJE)13009 was of the same family of parts, rated for higher current than the 13007. These are bipolar junction transistors, so don't try substituting the 13007 with MOSFETs. Substitute BJTs need to be either designed for switching power supplies (preferred) or for TV horizontal deflection (with appropriate voltage rating - in either case ... an MJE 13008, if still available, would be higher current, but lower voltage rating).

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

Just ordinary high-voltage, high-current NPN transistors, are they really anything special?

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Pics of my little geste.

-> LARGE -> LARGE -> LARGE

-> LARGE -> LARGE -> LARGE

-> LARGE -> LARGE

It's an old piece of junk with bad caps, fine for guinea pig.


Guess the next phase in the evolution of this disease should be start recapping things. A question for the fellow european forumers: Where do you buy online decent caps at fair prices?

[mariushm]

Re: Cheap PSU: Piece of junk or semi-decent?

I buy from Farnell and RS-Online ... but mostly Farnell.

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

Umm, I think you didnt have to spread the legs of the bridge rectifier so far, seems there are holes much closer. They usually make it the way they can solder in both diodes and rectifier.

I would personally first replace secondary rectifiers as if you recap it first, you may get not enough room to manipulate there which could result in the need of removal of the whole heatsink with rectifiers attached. Now you can swap them one after other and THAN replace caps. You may get stable 250 W from that, 300 W top with big enough input caps…

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

I buy from Farnell and RS-Online ... but mostly Farnell.

Thanks for the info!

[PeteS in CA]

Re: Cheap PSU: Piece of junk or semi-decent?

Motorola's MJE1300x series were among the first bipolar junction transistors designed for use in switching power supplies. Before Motorola's Switchmode series came out people used devices used in TV horizontal deflection circuits. In that sense MJE1300x transistors were/are special. But that was in the late 1970s, and power MOSFETs are far faster and allow switch frequencies higher than 40 or 50 KHz. So in that sense MJE1300x transistors are no longer special, just very good for 20 or 30 KHz switcchers - quality, performance and price. And match well with TL494 and 3524 type PWMs, which are also inexpensive. But good performance, quality and price are kind of special (assuming a good design and other parts choices, a big assumption).

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

What I mean is that I think vast majority of power NPN transistors can do the same as 1300x (and have similar or even better specs), for this reason it does not seem any special to me. Sure most technology was special when it was new, but yeah, if that's 1970 design

But there exist special types with really non-standard parameters, that's what I mean, whether 13007x are now amongst them, or amongst other common transistors, and it seems it's the latter one

[PeteS in CA]

Re: Cheap PSU: Piece of junk or semi-decent?

Well, as power switching BJTs go, I suppose an MJE13007 might be ordinary. As amplifier transistors go it's prbably not too good - it's optimized for switching. OTOH, high voltage amplifier transistors aren't going to do very well as power switches. "Special" or "ordinary" really are too simplistic. MJE13007 and family were designed in the mid 70s; so were the 8080 and Z80, which could be called revolutionary. Are the latter even available anymore except as surplus or used? Looked at that way, an MJE13007 could be seen as "special". If you'doing a 200KHz switcher, don't even bother with BJTs as they aren't adequate. IOW, simple categories don't work very well, sometimes.

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

For 200 kHz switcher I won't even try to use bipolar transistor. That's what FETs are for.

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Coming back to the 'TOOQ' PSU at the beginning of this thread, look at the voltage drop in +5V :




Under full throttle it drops below 4.5V :

-> LARGE


What do you think? Is there something we can do with the PSU to solve this, or better to kick away the piece of junk?

[c_hegge]

Re: Cheap PSU: Piece of junk or semi-decent?

Ignore it, unless you can confirm the readigns with a DMM. Those motherboard sensors are never right.

[Th3_uN1Qu3]

Re: Cheap PSU: Piece of junk or semi-decent?

I would be inclined to believe that the mobo is right. Judging by the FSB settings. that looks like either a PIII or AMD Socket A board, both of which have pretty much all their consumption on the 5V rail. When the PSU used is designed with newer computers in mind, that's what you get. Try a P4 or A64 or later system and see how it fares there.

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

It's more complicated. The sensors may be right, but there is always voltage drop accros the board so they measure lower voltage. On older boards with less copper it's even greater. But norm specifies voltage on the supply, the rest is MoBo maker's problem. So try to measure voltage even with this HW using multimeter. Does not have to be digital

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Reading on an empty molex the multimeter says 4.86V at idle, 4.81V full CPU load on +5V.

On +12V it is 12.32V/12.43V idle/load (+12V voltage increasing under load? ).

It's a venerable PIII slot-1 440BX mobo. Runs fine but there are occasional hang-ups, screen just frozing (no BSOD, no reboot).