Faulty 9VDC Power Supplies

[partyanimallighting]

Hi all,

I have a few LED spotlights that are constantly flashing on and off. From experience I know this normally means a faulty power supply so I pulled one apart and the power supply is very small (62MM x 30MM) and the input is 100~240VAC and the output is 9VDC feeding 7 1W LED doides (2 red, 2 green, 2 blue, 1 white). The circuitry seems simple enough so I figured I could throw this out at you gurus to pinpoint what might be the defective part, probably source it locally and swap it out. Any help would be greatly appreciated. Here are the pix.

 

[dorke]

You have a bulged capacitor (C6).
That would be a typical fault of a SMPS like this one.
Replace it.

 

[Harald Kapp]

When buying the replacement, look for a "low ESR" type. Take care the max. voltage and the capacity match the values on the existing capacitor. Note also that this is a 105 °C rated capacitor. The replacement should also be rated at 105 °C (or higher) as the power supply will get very warm inside.

 

[partyanimallighting]

Thanks! That was a quick response! I've narrowed the problematic units down to 3 in total and I've checked all 3 units with an alternative power supply and all function properly with this power supply so these three definitely have faulty power supplies. I'm assuming this capacitor will be the issue with all three defective power supplies so I'll pull one of the capacitors, replace it and update you accordingly.

 

[partyanimallighting]

Pulled one. 330mF 16V 105 Deg. I checked all the available parts stores and none have the values. Any replacement options as per different values?

 

[(*steve*)]

Look for 330μF 16V 105C, low ESR.

The other important criteria is size -- make sure it will fit.

Low ESR capacitors tend to be a little larger for their capacitance, but the size for a given capacitance gets smaller and smaller as technology progresses.

Higher capacitance (say 470μF -- a common value) is ok, as is a higher voltage rating.

These capacitors are polarised, so remember which way it came out. If you forget, the positive lead often has a square pad on the PCB. Long lead into square pad. Otherwise the negative output will likely connect to the negative capacitor lead, and positive to positive.

 

[partyanimallighting]

So I can use a higher microfarad value? 470uf as you mentioned above? But the voltage should be 16V right? If I find a replacement, I know they're polarized and they will have to be put back in the correct polarity.

 

[dorke]

Yes you can use a 470uF, voltage can be higher than 16V as well.
But note that your space is very limited and larger value caps as well as voltage may be to big to fit in.

BTW,
it is strange you couldn't find a 330uF.

 

[partyanimallighting]

Backward 3rd. World Caribbean island. Beautiful island though, Trinidad. Well, here's the update. I pulled out some old blown PCB's and I found some with 470uf 16V 105 deg. capacitors, so i pulled out one, soldered it into the defective PCB, powered up and voila!!! No more flashing!! Thanks so much!! Now to sort out the other two units. By the way, will putting in a higher value microfarad cause any issues? Overheating? Higher power draw?

 

[dorke]

No problems,actually higher Cap value is better.
They use the minimum value and voltage because they yield lower size and cost.

Yep,
tropical islands paradise ,Hurricane season can be a scary experience though.

 

[partyanimallighting]

We're way down South. Right next to Venezuela so most of them past North of us. Sometimes....... We've been hit before and we'll be hit again.

 

[partyanimallighting]

Right!! Got two of the three defective units repaired, re-assembled and fully functional. However......... one power supply still has problems, no DC output. I changed out the cap on this PS also but it probably has another problem. I've taken a close look at it and I don't see anything suspicious but I'm not a trained techie. There's a small inline fuse at the AC line in and it checked out for continuity. From here on that's where I seek the wisdom of the gurus.

 

[73's de Edd]

Sir partyanimallighting

PRELIMINARY . . . .

IF you have the physical mounting room, the use of double or triple electrolytics to accomplish your summed capacitance, can APPRECIABLY increase the long time life and reliability of a rectified secondary windings supply filtering.
In this manner, the filtering (and self induced heating) gets spread out through the mass of extra separate foil areas.

Check this schematic out . . . . and see if my eagle eyes have read that U1 " switch mode power supply in a chip" as being one of Fairchilds FSDMO265R.
Nevernohowsomever . . . should it be using one of a most honnable Chinee knock off I.C.'s, its prefix may have a variance, but the basic . . .265R identifier . . . should be carried forward.

Your two other units were failed by the agressive capacitance decline of the VIOLET circled secondary filter cap . . .with its mere replacment restoring operation.
On your final straggler / problematic unit, the NEXT most suspect capacitor would be the C2 capacitor, ( GREEN circle ) being used for the powering of U1.

PHOTO REFERENCING MARKUP . . . .

TESTEE-TESTEE . . . .

Initially clean the board of all of the flux residue, to make it look better and to better see all the solder joints and inspect to see that there are no solder ring joints that are just floating around a component lead.
Take metering in hand and go DC mode in excess of 300VDC range (insurance) and check to confirm B+ across the main filter cap and then hold the negative and swing positive on up to common
multi interconnected pins # 6-7-8 of the IC to confirm if B+ is making it all the way to there also.
Update us on your findings.

73's de Edd

 

[davenn]

Check this schematic out . . . . and see if my eagle eyes have read that U1 " switch mode power supply in a chip" as being one of Fairchilds FSDMO265R.
Nevernohowsomever . . . should it be using one of a most honnable Chinee knock off I.C.'s, its prefix may have a variance, but the basic . . .265R identifier . . . should be carried forward.

Edd, I would strongly suggest that you have your line filter 90 deg out of whack and that the left coil in your diag is shorting out the mains input


Dave

 

[partyanimallighting]

Hi Edd and everyone else! I was off island for the weekend for a wedding gig and got back in yesterday. Here's the thing....I can do basic repairs, tracing, testing etc. but Edd!!! What did you try to explain to me??? That just shot straight over my head and I am totally clueless as to what you were trying to explain (Picture me in kinder garden electronics repair with a AA battery, two pieces of wire and a flashlight bulb!). Electrolytics? Secondary windings? 265R identifier? Confirm B+? hold the negative and swing positive on up to common? This sounds like a script from Star Trek to me!! I'm totally lost but I'm thinking that you want me to test for DC voltage at the large capacitor, which I assume is the "power filter capacitor" and you also want me to check the voltages at pins 6, 7 and 8 at the IC U1, (pin1 is the one with the dot!!! I know this!!) which I assume will be those 3 next to the coil. Tell me I'm right here so I don't feel so moronic.......and be gentle

 

[partyanimallighting]

OK. Did some excavation and one of the coils is broken off from the base and was held in place by hot glue so I'm sure this could be the problem. I checked my spare parts bins and found another power supply (24VDC) which has a similar sized coil so......can I use this coil? I also pulled the capacitor that Ed thought might be "iffy". It's 47μf 25V and I found a 47μf 50V which I can fit (barely).

 

[dorke]

BTW,
That Chinese CapXon brand is very well known for making crappy failing power supply caps.
I have replaced quit a few of them myself.

 

[partyanimallighting]

So I should replace this capacitor anyway....will the higher voltage work without problems? And what about the coil?

 

[dorke]

You don't need to replace the cap if it isn't bad.
But you can while you are already "at it".
The higher voltage isn't a problem,the new cap should be"low ESR" type" .

If the coil is broken replace it as well.

 

[partyanimallighting]

Will the coil from the other power supply work? Do these coils have specific values and what is the purpose of the coil? Remember I'm going through a learning process here.