[Solved] Repair / DC 3.3V 2.5A Open Frame Power Supply / Network Switch

[xan]

Hi everyone,
i need some help and tips to fix an Open Frame Power Supply DC 3.3V 2.5A what i can do 1st ? fuse it's ok....

Leader Electronics
Input Voltage: 100 ~ 240VAC ~ 50/60Hz. 0.3A
Outputs: DC +3.3V === 2.5A
MODEL: SB10-033100-10

Thank's for support!

[singapol]

The cap arrowed in red has a bulged top. Check esr and capacitance.

[xan]

i don't have esr tool  some workaround? i test capacity right now!

Thank's

[bktemp]

If you are not sure which capacitor is bad, replace all capacitors. The mains rated capacitor rarely fails, so it is probably fine. The secondary side capacitors and the small capacitor next to the SMPS controller ic fail quite often.

[xan]

Ok i got it! and with my multimeter can i do some cap measurements? or not?(i'm not so expert)

[xan]

ok green caps is gone it marks teapo 1000uF 10v.. can i use as replacement 1200uF 16v?

[Bushougoma]

A bulged cap is a replace on sight part no need to test it. It has indeed failed.

ESR and capacitance measurements are independent of one another I have measured bad capacitors that had good capacitance but high ESR and vice versa.

Electrolytics typically have a tolerance of +-20% so a 1200uF will be fine.

Just make sure it's a low ESR type and it's ESR is equal to or less than the original capacitors and it's max ripple current is equal to or greater than the originals. Check the datasheet for the original cap and your replacement cap to verify. General purpose caps can't be used on the high frequency output of a switch mode power supply.

I would replace both of the secondary caps and the small bootstrap (start) cap near the PWM / Switching transistor DIP IC that may be all you need to get it working.

If not these integrated supplies with the PWM IC and the switching transistor in one package are pretty easy to troubleshoot due to the low component count.

[xan]

Thank's really understood

for the green caps could you check sheets ?

original -> http://www.teapo.com/WebSiteFile/Products/Product_Data/SC.pdf
new -> http://www.nfjapan.com/datasheet/KZG.pdf

(sorry for ask but i'm really newbie in this kind of things and i want to understand!)

[Bushougoma]

No problem it can be a bit confusing.

On the Teapo datasheet provided ESR is listed as Z which is short for Impedance.

I've highlighted the critical specs you first find the working voltage of the cap at the top, then the capacitance on the left, then go to the proper column. You'll notice the ESR (Z) and ripple varies based on the capacitor case size so you'll have to measure the cap with a digital caliper or ruler and use those measurements to determine it's ESR and max ripple current.

Ripple on the replacement capacitor should be => original capacitor. ESR (Z) on the replacement capacitor should be <= original capacitor.

I can't find a 1200uF cap at 16 volts in the Chemicon datasheet you provided. In that series 1200uF only comes in 6.3 volts which won't work since the original capacitor has a working voltage of 10 volts.

[xan]

Ahhh understood.. i need to check more few things.. i keep you updated later... Thnak's again!

[xan]

Ok guys finally!!
old caps green and new cap blu but .... SAMXON cap have 85° instead of 105° (same 1000uF - 10V).. should be ok ? or?
can you check sheets for me?

[Bushougoma]

You can't go down in temperature rating from the original capacitors only up. You'll notice most caps will have a temperature in Celsius printed on the side (85C and 105C are the most common) that is the max operating temperature they are rated for. You can replace 85C rated caps with 105C but not the reverse.

I've never seen an 85C cap from a top tier cap manufacturer that was low ESR without even looking at the datasheet I would say that blue 85C capacitor was general purpose.

[xan]

  damn ok... i will look for another... sorry for asking.. i keep you updated again!

[Monkeh]

Go to ebay, spend €2. Fixed.

[Armadillo]

Why don't you install the samxon Cap in first and see if it fully repaired the power supply or there are some other components to order at the same time, in the name of efficiency. However, there are also economics you should consider aside from electronics repair. 

[xan]

mm right! i will try, i think maybe i will order some other parts... tnx.

[Armadillo]

Can you confirm that the IC is A6351. Please take a close up if you can.
What are the symptoms when you power up the power supply?

[The open frame exposes lethal voltages, do not touch when power is up, always unplug and discharge capacitor, so please be extremely careful with it as capacitor may be charged. The best is to power up with 100W incandescent bulb in series with the mains].

If you are not sure of what you are doing, please do not do it. thanks.

By the way, what instruments or meter do you posses?.

[xan]

Yes thank's i will not touch it!!!  if i'm not feel secure i will ask before! i have a cheap multimeter.. excel multimeter.. for now i still wait to find right capacitor for substitution, from old pcb.
The Symptoms was simply, network switch power led blinking green and network on LAN was Down!

[Armadillo]

There are effectively 2 capacitors at the output, so whether you install the one capacitor or not, it should still read 3.3vdc. To troubleshoot, please measure if only you can, as shown in the picture below.

Use multimeter, put to "DC voltage range" measure:

[xan]

Damn i just desolder bad caps... how i can test 3.3v now  ? i will resolder it back but i think there isn't the right voltage there... obiviously!
IC on screen. Tnx

[Armadillo]

you do not need to solder the bad cap, just leave it, because there is already another cap on the board. It is also 1000uF 10V. We are just troubleshooting the problems now, to identify other areas causing the problems. You can install the new cap when it come. For now, don't need to, just leave it un-installed, vacant.!

Do you understand what I mean, the 2 capacitors are effectively in parallel across a choke. So one down, still not a big problem as far as DC is concerned.

[xan]

Ah.. Ok You welcome ! sorry for asking i'm newmbie but i can't do measurements right now i'm not on my lab... right now i will do it later! i keep you updated ! Thank's for the tips.
Later

[xan]

i still wait to be back to my lab on this weekend so i can't test 3.3 lines ... but can i ask you somethings armadillo?
1st) what do you mean with:

 

[The open frame exposes lethal voltages, do not touch when power is up, always unplug and discharge capacitor, so please be extremely careful with it as capacitor may be charged. The best is to power up with 100W incandescent bulb in series with the mains].

2nd) why in this board there are 2 caps in parallel across the chocke? what are their functions if i can test it or use it without one ?

Thank's (i'm just so curious to understand!)

[Armadillo]

1st) what do you mean with:

 

[The open frame exposes lethal voltages, do not touch when power is up, always unplug and discharge capacitor, so please be extremely careful with it as capacitor may be charged. The best is to power up with 100W incandescent bulb in series with the mains].

2nd) why in this board there are 2 caps in parallel across the chocke? what are their functions if i can test it or use it without one ?

Reply #1: Please refer the load lamp safety at http://www.bristolwatch.com/load_lamp.htm . The purpose is to protect the device under test by limiting the current in case the device is shorted somewhere e.g. to minimize possibility of output transistor or mosfet from being damaged or burned. The power supply is normally segregated into 2 sections, the primary section and the secondary section. The primary section after the diode bridge is about 300vdc. Copper tracks underside of the board or the components leads exposes this high voltage. Accidental touching it can be lethal.

Reply #2: You can view it as 2 stage filters. The choke / inductor with the 2nd capacitor further improve the DC filtering of ripple voltage. The choke act as a resistor to high frequency switching ripple current because the inductive reactance is directly proportional to the frequency, stop high frequency noise / ripple while allowing DC to cross to the 2nd capacitor. After the choke, then the 2nd capacitor further filter it. For troubleshooting purposes like measuring the 3.3 vdc, single stage filter will do. In case you want to measure the performance of the power supply ripple voltage, then you can use a oscilloscope to measure it after the 2nd stage filter, for example.

Hope these clarify your questions.

[xan]

Ok Finally i was back to my Lab (after 10 days of full workload  ) i change the capacitor with a new one and i made the measurements! here the screens... from power supplies come a strange sound like somethings it's activated and then deactivated .. "tik tik tik tik tik tik tik tik tik " still have blinking led ... -_- i measure at the -/+ terminals about oscillating from 2.6 to 2.9 V on both -/+ .... Ufff... some tips guys ??  !SCREEN DOWN!