Out of spec 12v and 5v. Recommendations?

[MixMasta]

I have a few power supplies where the 12v is pretty low and the 5v is high. I also have a couple where just the opposite is occuring, 12v is at like 13.3 and the 5v is somewhere around 4.5v. I have at least one where the voltage drops when the 12v is under load. Many of these have Fuhjyyu caps, but none appear to be leaking. Could they be causing these conditions? Any recommendations or background info on this condition would be great. (Maybe a crash course on how the 12v and 5v is regulated is already on the forum, but I guess I missed it then.) I'm thinking about replacing some of the caps, but I'm not sure if its worth the investment. I'd hate to order a bunch of caps, only to find that my situation with out of range voltage remains the same. What are the chances that my 12v and 5v would be within 5% of spec with new caps, these being apparently not so great power supplies and all? How do I test a cap anyway, all I own is a Radio Shack multimeter? And why is it such a pain to get the circuit board out of the power supply housing? Am I supposed to desolder the on/off switch to get the thing completely out? Anyone want me to send them ~10 ps to evaluate whether they are worth saving?

[japlytic]

Re: Out of spec 12v and 5v. Recommendations?

If you still get out of spec 12V and 5V rails after replacing the electrolytic capacitors, check out the high power rectifiers. In some units I have seen, the current ratings of the output rectifiers are less than the output current rating printed on the power supply.

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

Aren't they the same rail on the cheaper power supplies? Some of mine have a pots inside. Adjusting it causes both the 5v and 12v to increase or decrease. I can't adjust either separately.

If you still get out of spec 12V and 5V rails after replacing the electrolytic capacitors, check out the high power rectifiers. In some units I have seen, the current ratings of the output rectifiers are less than the output current rating printed on the power supply.

[davmax]

Re: Out of spec 12v and 5v. Recommendations?

One adjustment means one regulating circuit just monitoring one of the outputs often only the 5 volt output. This means all other outputs are relative to the one monitored. None are on the same rail. Sometimes low current outputs will take power from a higher voltage rail, but because this is done with a regulating chip that dissipates heat, it is definitely for low current outputs only.

[linuxguru]

Re: Out of spec 12v and 5v. Recommendations?

> Adjusting it causes both the 5v and 12v to increase or decrease. I can't adjust either separately.

Most of the secondary circuits regulate both the +5v and +12v with one feedback loop. Both voltages are sensed with a simple resistive wye-divider with one leg to ground, and compared with a reference voltage, usually +2.5v from a TL431 band-gap reference. That's the reason that +5v will
increase when +12v drops (on heavy loading) and vice versa.

If you find that it's dropping on light cross-loading, then it's most probably a bad caps issue. Replace all secondary caps as usual with the recommended replacements (from other threads on this forum). Fuhjyyu is a known bad cap, and it's alarming that even reputed brands like FSP (Fortron-Sparkle) have been using them extensively.

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

> Fuhjyyu is a known bad cap, and it's alarming that even reputed brands like FSP (Fortron-Sparkle) have been using them extensively.

Yes, I have 2 FSP (one of which is rebranded Sparkle) with the Fuhjyyu caps! I don't really know what brand of power supply is reliable any more. I have another 2 bad Antec ones...

[gonzo0815]

Re: Out of spec 12v and 5v. Recommendations?

As far as i know, not much on the lower price tag, and a few at the higher. I normaly go for cheap, most FSP`s oem i had are at least equiped with Teapo caps, wich is fine methink.
Some FSP oem's from MDM are obviousely equiped with not that good caps, IMHO due to the price pressure from the oem customer (some 250w units, mostly sold with some Medion p4 3ghz systems without the needed airflow, to keep it silent but very hot)
Any way, for personall use, i think recapping a psu will not hurt and is well worth the effort, if the rest of the circuit is of honest enginering work. It is not that hard to do it, because the soldering is in most cases very easy, with an high wattage sodering iron.

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

Damnit. These things are full of 10v 3300 uF 10mm and 16v 2200 uF 10mm. Maybe I'll just throw them away.

[linuxguru]

Re: Out of spec 12v and 5v. Recommendations?

FSP and Channel Well are known for stuffing their PSUs with Fuhjyyu 10 mm caps. The 1650uF/16v/10mm is infamous, but even worse are the 4700uF/10v/10mm and the 3300uF/16v/10mm. I'm still looking for inexpensive universal low-ESR caps, and I've only turned up Taicon HD 1200uF/16v/10x25mm - which has worked well so far.

[kc8adu]

Re: Out of spec 12v and 5v. Recommendations?

Damnit. These things are full of 10v 3300 uF 10mm and 16v 2200 uF 10mm. Maybe I'll just throw them away.

i have found that i can get most of the fsp units to take 12.5mm caps.sometimes they have to stay 1/2 in or so off the board but it doesnt seem to hurt.i have several 350-400 w fsp units in my own stuff that have all 12.5 mm caps.iff i need 10mm i use ncc lxz 2700@6.3.
but most places i use rubycon yxg 3300@6.3.they outperform the fuhjjyu's even though they are old school as low esr caps go.
and it helps that i stumbled onto 3000 of them dirt cheap at a hamfest :-)

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

Sorry to bring this thread back but...

Replaced all large caps on a FSP ATX-350PA and I still have a low 5v and high 12v. If I adjust the pots, I can get 5v at 5.00 and 12v at 12.95v with no load. Plug it into a pc, and the 5v drops to 4.82 and the 12v jumps to 13.49. Obviously, I'll want to adjust the pots while the supply is under load, but not while the 12v is so out of whack (yeah 14v is crazy). What should I look for... and assume I have little knowledge of a powersupply, and my only real tools are a multimeter and soldering station.

[Brian C]

Re: Out of spec 12v and 5v. Recommendations?

There are few resistors other than the trimmer pot to adjust the balance between 5V and 12V line. Can u take a photo of the parts around PWM IC (TL494, KA7500, etc)... The 5V and 12V line are summed to the feedback of PWM controller IC.

SMPS has minimum load condition for high power output like 5V and 12V. Load the P/S with this condition and adjust the resistor value. (pls check the minimum load current from the specification label)

Since 5V and 12V share some part of the secondary windings, Loading on the 5V line will cause significant increase in 12V line and vice versa (if one supply line is left unloaded). The effect is not so significant when both are well loaded.

It is quite hard to achieve tighter regulation on low end ATX P/S.

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

Here are some pics... apparently I am not very good at taking them... how does everyone else get such clear ones? Anyway, what should I do now?

[Shroomie]

Re: Out of spec 12v and 5v. Recommendations?

"Good lighting, no flash" works for me. The flash is terrible with electronic components, but a fluorescent light or sunlight tends to create a good picture, even with an older camera like mine (2 megapixel Kodak EasyShare).

Still, those pictures aren't bad at all.

[Brian C]

Re: Out of spec 12v and 5v. Recommendations?

What is the IC part no. in the picture ? It is probably the PWM controller IC.

[gonzo0815]

Re: Out of spec 12v and 5v. Recommendations?

Most important is, that the cam has a macro mode, withouth that, i have had no luck (ok, only have had lend some cheaper cams (about 120€). Withouth that i haven`t got sharp pictures of elektronic devices.

[willawake]

Re: Out of spec 12v and 5v. Recommendations?

most importantly make sure you are not going closer than the minimum focusing distance of the camera.
enable macro mode
dont zoom
best results are on a tripod or mini tripod with flash disabled. the camera will do a 1s or 2 sec exposure. but for that you have to enable the timer so you can press the button and the camera will stop shaking on the tripod before it takes the pic. sometimes flash is necessary though to show stuff in shadow.

one problem is depth of field. at large apertures (say f2.8) the depth of field may be very shallow. so while you focus on one component and it is in focus, everything closer or further away will be out of focus. check if thats the issue.

sometimes the camera is just focusing on something which you did not intend to focus on.

and actually i get better close up product shot pics with my canon a700 than my DSLR. (although the a700 makes the corner of the photo dark cos the lens makes a shadow with the flash). so dont blame the equipment.

[Rainbow]

Re: Out of spec 12v and 5v. Recommendations?

I use Canon Powershot G3 with flash power set to -2 (minimum), macro mode and either f2.0 or f8.0 (for minimum/maximum focus depth) depending on my needs.

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

FJ 3528
536 J771C

The FJ part is a logo...

willawake, I enjoy all your yatch photos. They are really great. Even cooler to me (a lover of ancient greek history and mythology) is that many are taken at Piraeus.

[MixMasta]

Re: Out of spec 12v and 5v. Recommendations?

Guess I will remove these caps I wasted my time putting on cause I don't know how to fix this problem... what a waste.