General PSU Discussion and FAQ contributions

[moe2020]

Re: General PSU Discussion and FAQ contributions

Hello all, this is my first post here, so please be kind
I have a couple of power SMPS power supplies, that are doing some wired stuff:
one of them, the Vcc (pin 7) of the UC3842, is fluctuating, it does seem to get to 16V, since I do see the square pulse on pin 6, but it is fluctuating between 13v and 10v!!
I have replaced the power IC, all caps and made sure all the resistors associated with this device are good. I use the light bulb to check the parts, since If I power it with the fuse in place, the rectifiers get very hot and short out...
The second one, is, I am getting about 70v after the start up resistor!! I back tracked it,
on a good board I have about 105v DC on the output of the bridge rectifier , but reading 155v DC on the non-working unit...if I lift the +dc output pin from the PCB, then it drops to 95v, put it back, the DC output voltage goes up to 155v dc.
If I am not providing enough information, please excuse me, but will be more than happy to expand on what I have posted here. your help is greatly appreciated.

[Pentium4]

Re: General PSU Discussion and FAQ contributions

Does anyone have some tips on how to remove or clean off the white stuff that is covering a lot of the PSU components that appear either to be used for a sort of tamper proof, or to hold the components more securely?

A lot of companies use glue to hold components in place to improve production times. If the glue is white, you can leave it (If there's a lot of it though I try to remove most) but if the glue is tan or brown, you need to remove it as it will go conductive over time. I usually remove the components covered in glue to access the glue easier for cleaning, and just heating the board helps a lot with getting it off. I use pliers too

[Roving Geek]

Re: General PSU Discussion and FAQ contributions

Does anyone have some tips on how to remove or clean off the white stuff that is covering a lot of the PSU components that appear either to be used for a sort of tamper proof, or to hold the components more securely?

[Panzer_green]

Re: General PSU Discussion and FAQ contributions

I have a Samsung Plasma (ps51d6900dm) turning on issue:- The problem is the tv turns on and gets to the logo but then turns off! tries 3 times and for safety reasons stops trying to turn the tv on i believe.
I did a few checks and by no means am i very knowledgeable when it comes to fixing tv's but i checked all my voltages and they seem to be fine and disconnected other boards yet still came to the conclusion its the power supply.

I then heard about heating the board with a hairdryer to see if it turns on! which it did turn on. So i isolated it to a part of the board and found when i pushed on the IC the tv stayed on when not heated. I then believed it was a cold solder joint. It worked after re soldering this area for a week! then the same problem happened again! Is this part likely to be causing this problem and if so where can i get this part as i have had no luck looking myself!

Photo of IC i believe is faulty! in link
http://www.avsforum.com/forum/attach...7&d=1408930516

[zrx8]

Re: General PSU Discussion and FAQ contributions

Hello,

The fan in my ATX PSU stopped spinning. It is clean however, not jammed, and works properly when connected directly to +12V. The PSU's type as it is printed on the PCB is FSP400-60GLY (labeled Gigabyte 460W on the outside of the casing, figures... ). When turned on, the fan spins a few times, then it stops. Unfortunately I cannot find a shematic for this model, found another for a similar one (FSP500-60GLN) on this forum, but it seems to be incomplete. Can you please give me any hint on this ?
Thanks in advance, Peter

[Dluisao]

Re: General PSU Discussion and FAQ contributions

hello yes capacitor must be change

[cruyffcb]

Re: General PSU Discussion and FAQ contributions

plus tôt changé les deux condos . C877 ET C878

[Norfolktvrepairs]

Re: General PSU Discussion and FAQ contributions

Hi I have a 715t2463-3 psu for a aoc 32" tv, the fault it's having is that it fires up the shuts down after 5 secs to a flashing orange light, I have changed several of the caps but still do the same has anyone else coming across this problem

[prongs12]

Re: General PSU Discussion and FAQ contributions

could anyone share a what to do list for repair power suply.. starting from cheking the suspicious broken part...

and now I'm share some of my experience.. in repair PSU

PSU short.... chek rectifier diode... and replace with similar parts

no power but 5vsb..... chek primary power transistor or nfet..do search in replacement data sheet.. and replace it with same similar parts that has similar value in datasheet....

strange sound on psu.... replace primary (biggest one) capacitor......

that's all

[MHVishal]

Re: General PSU Discussion and FAQ contributions

I read it could be due to failing capacitors and a PSU change is called for ...apparently those bundled in CPU packages tend to be less than top quality
Good i nice to you

[grss1982]

Re: General PSU Discussion and FAQ contributions

Just a quick question:

When the PSU's "-12v" is reading "0.97v" is that a sign of impeding death????

[starfury1]

Re: General PSU Discussion and FAQ contributions

looks like the very simple bock diagram link above has died

So thought id fix it with another link and then decided to round it up a bit
So hope no one minds

Here is the wiki on Switched-mode power supply

The Wiki should help expand on PeteS's Great written explanation of
"How SM-PSU's works"
posted above.


Here is a photo from the Wiki of the "typical supply" outlined in this thread (large 3Meg file at Wiki)



Copyright notice from wiki photo....
Public domain I, the copyright holder of this work, hereby release it into the public domain. This applies worldwide.
I, grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.


Here is a BAD example of the Above


Copyright Me and BADCAPS for anybody that cares

I should add that the outline here is of Now older technology
It is still the basis of how they work regardless.

The next evolution and mostly what you going to see is the above but with a modified Mains side to Incorporate What is know as
"Active Power Factor Correction" A-PFC
(thats putting it simply, and the construction,Design does go further then that in reality)

This is what your more likely to see these days
NOTE the small PCB and 1 large Capacitor, that should be a bit of a giveaway its an APFC type.
(but there are exceptions to any rule of thumb and the really big PSU's will probably have two
and some older ones may have 1 (I think), bottom line check!!!)



Liberty 620W (some of these have been known to go boom!)

Check this thread out for photos of the many variations and themes you find with SMPSU (thanks go to Dood)

Power supply build quality pictorial

Thanks PeteS for the Excellent work you did and others for contributing to it.

Cheers

[starfury1]

Re: General PSU Discussion and FAQ contributions

bit dated but may help you


ATX 200W TL494

here SG6105 controller

very simple block diagram here

not really a block but might help with peteS explanation above

Here


pc psu site here

some what on the technical side PDF here

The FAQ here

seek on the net and ye shall find...well mostly

HTH cheers

[bgavin]

Re: General PSU Discussion and FAQ contributions

Could somebody post a block diagram or schematic for a typical ATX supply. I would like to learn more about where the various caps fall in the circuit, and relate it back to Pete's Seven Step Program above.

[andrewb]

Re: Power Supply Design Description (first post is long)

Any thoughts on active Power Factor Correction, I have had some experience with this additional piece in the PSU puzzle, but is it going to become commonplace for most PC PSU's. The units I have seen so far
have extra devices like LT1249 and the power mosfet it controls, switches across the output of the main rectifier. ( This takes some understanding)
Not directly though, it does use a type of snubber to absorb/redistribute
the energy.
It seems that when things go wrong with this part of the circuit,
they go horribly wrong (at least in my experience).
I'm still having some trouble comming to grips with the application/implementation some engineers have decided upon.

http://focus.ti.com/docs/prod/folders/print/uc3853.html
http://www.onsemi.com/PowerSolutions....do?id=MC33262
http://www.linear.com/pc/productDeta...42,C1138,P1417

It may eventually make a difference, to power consumption, but it is also adding a curve ball for us techs.
Andrew

[arneson]

Re: Power Supply Design Description (first post is long)

The multi voltage high amperage switching power supplies have always boggled me.
I just replace them thinking that when the go they're gone, chared and burnt.
For some reason i don't dispose of them and have a closet full.
I have modified some PSU's but have not been able to repair them.
Your description is very helpful and the links to chip specs a nice touch.
My IC Master is way outdated and HW Sams may have Photophacts going back to Edison's day but not to much help today.
Sorry to ramble, I'd love to find a typical schematic for one of these.

[Rainbow]

Re: Power Supply Design Description (first post is long)

KA7500B is pin-compatible with TL494 - they can be interchanged. They are also used on some ECS/PC Chips boards (like K7S5A) for CPU power, some older boards (like M726MRT) use MC3842 (or UC3842 or something3842 - they're same). I've never seen these chips bad on a board, however I've seen many of the special VRM controllers dead (because of PSU or shorted mosfet).

[PeteS in CA]

Re: Power Supply Design Description (first post is long)

Here are links to TI's datasheets for three of the most common pulse width modulator ICs:

SG3524 (KA7500 is similar): https://cdn.badcaps-static.com/pdfs/...0b64dfc01f.pdf

TL494: https://cdn.badcaps-static.com/pdfs/...22b539cab9.pdf

UC3842: https://cdn.badcaps-static.com/pdfs/...7f7a055a4f.pdf

The datasheets incude chip schematics, descriptions of how the ICs operate, and sample application circuits. The SG3524 was introduced in 1975; the TL494 a few years later. The UC3842 family is newer, introduced in the mid-80s. Good stuff remains usable for a long time.

[kc8adu]

Re: Power Supply Design Description (first post is long)

looks good to me.
good work!

[PeteS in CA]

Re: Power Supply Design Description (first post is long)

Please PM me with suggestions where this isn't clear and with GP questions. I'll update the first post A/R and answer Qs by PM or here.