Switching Power Supply Repair

For the past few days I've been trying to fix this dead triple output switching power supply adapter (PSU25A-14E)

After I opened the case, I saw six bulging electrolytic capacitors (4x 330uF 25V and 2x 2700uF 6.3V) and one blown IC controller (TOP234YN)

I replaced them all, and I also checked the components (two ceramic caps, two rectifier diodes) near the IC for wrong values, etc., and they all passed.

Plugged in the AC power cable, and nothing happened.

Another check with my multimeter, I found the main fuse (Littelfuse 382 cylinder fuse rated 2A 250V) has no continuity. So I pulled it out.

Because I don't have a suitable replacement fuse yet, I thought I'd be able to continue checking the power supply if I temporarily re-establish the fuse connection by soldering in a piece of thick wire (bad idea?)

Plugged in the AC power cable again. DC output power LED indicator turned on! and my house circuit breaker tripped!

Any ideas why it happened?

What usually takes caps out is over voltage. Ditto ICs. So it looks like something upstream of these components is the real fault.  The rest is collateral damage.

Cheers

Ian

metalb00b00 said:

For the past few days I've been trying to fix this dead triple output switching power supply adapter (PSU25A-14E)

Click to expand...

FIY MeanWell GP25A14E-R1B is $30 USD on Mouser.

squarewave said:

FIY MeanWell GP25A14E-R1B is $30 USD on Mouser.

Click to expand...

True, but with $75 shipping fee and $20 import tax, it's no longer $30.

OTOH, a local component store sold me the TOP234YN IC controller for $3/pc, the main fuse for $0.02/pc (I bought 5), and the caps cost basically nothing.

So yeah, I'd rather fix it.

ruffrecords said:

What usually takes caps out is over voltage. Ditto ICs. So it looks like something upstream of these components is the real fault.  The rest is collateral damage.

Cheers

Ian

Click to expand...

Other than my house circuit breaker tripped if I switched this adapter on, nothing else seemed to go out of ordinary. No spark or smoke or funny smell when it happened. Like I mentioned earlier, the DC output LED indicator even lit up. Anyway, I have removed the piece of wire that I used temporarily as a fuse and will solder in the actual fuse when I have it later this evening.
Really hoping that is all the problem it had

Bad caps.

https://www.dropbox.com/s/t4cl9f204xanmig/IMG_20180222_012819.jpg

Blown switching controller IC.

https://www.dropbox.com/s/15ss5n4xqzi6og2/IMG_20180222_012455.jpg

Caps replaced.

https://www.dropbox.com/s/mpzc2nzofcgwkw1/IMG_20180222_012335.jpg

IC replaced.

https://www.dropbox.com/s/e8634zo2wwzahv8/IMG_20180222_012220.jpg

Blown fuse removed. PCB trace layer.

https://www.dropbox.com/s/gijewc6xzzz2p20/IMG_20180222_012125.jpg

Blown fuse removed. PCB top side.

https://www.dropbox.com/s/afxzxe6w3gl4hmi/IMG_20180222_012249.jpg

Blown fuse.

https://www.dropbox.com/s/dp5ci7f92no52s5/IMG_20180222_013126.jpg

The bridge rectifier, the bulk capacitor and the two EMI filter X1 type capacitors, all went bad after that test.

From 2006 in the Meta
https://groupdiy.com/index.php?topic=19733

"(bad idea?)"


Did your dad used to put a penny in the fuse box?

metalb00b00 said:

Because I don't have a suitable replacement fuse yet, I thought I'd be able to continue checking the power supply if I temporarily re-establish the fuse connection by soldering in a piece of thick wire (bad idea?)

Plugged in the AC power cable again. DC output power LED indicator turned on! and my house circuit breaker tripped!

Any ideas why it happened?

Click to expand...

Indeed lucky that your mains breaker prevented a fire.

In the past I have Macgyvered a fuse using a single stand of copper wire... There are look up tables on the WWW and my thin single strand wire fuse was still around 10A..

Be careful...

JR

Roly said:

"(bad idea?)"


Did your dad used to put a penny in the fuse box?

Click to expand...

You misunderstood. The fuse that I replaced with a thick wire was the small 2A 250V that was on the primary side of this power supply, not the main fuse of my house.

metalb00b00 said:

You misunderstood. The fuse that I replaced with a thick wire was the small 2A 250V that was on the primary side of this power supply, not the main fuse of my house.

Click to expand...

No his point was you defeated the fuse (a heavy wire will have a fuse current well in excess of any breaker).... Tripping mains fuses should not be considered a reliable backup for product fuses.

Mains voltage times breaker trip current is a lot of watts of fire starting energy. A fault that doesn't trip the mains breaker could still do a lot of damage (thousands of watts).

JR

PS: My house fuse box still uses edison fuse bases, so a penny could fit.  :.. In fact I have replaced and thrown away a bunch of 30A fuses that the former resident of my house used... IIRC US code restricts branches to 20A (I use 15A fuses now). Back in the day, a number of house fires were blamed on sticking a penny in the fuse box, to replace a blown fuse.

> IIRC US code restricts branches to 20A (I use 15A fuses now).

It goes by the *wire*.

#14 should be fused 15A.

#12 can be fused 20A.

If I am guessing the vintage and sophistication of your house, it may be all #14. A rural 1948 house near here is.

Also FWIW: insurance companies are down on fuseboxes (for reasons you explained). That old house had a fine fusebox ripped out and a tired undersize breaker box recklessly hay-wired in. This *may* not kick-in until you go to sell the house. Since you appear to be set to live there forever, you may not care.

those switchers are like a Mazerati,  precisely tuned to handle all that power with small lightweight components, ioe thing goes wrong and it wipes out the while enchilada,

tale this Ice Power module for an example. power supply and amp all on one small lightweight board, fabulous!

until it breaks,  call the company, they say no schematic, fixing it yourself could burn your house down, please send $87.50 and you are good for another four years.

what is the alternative? build a power supply and push-pull amp? how much would that cost? how much would it weigh? how much time will it take to build?
they pretty much got you by the cajones, this switch mode racket,

fine pitch propriety chips, not sold at Radio Shack. or digimouser. wtf?    ??? ???

no wonder they call it ice power, that company is as cold as ice, 

upload still down, so pic here>

http://www.fullcompass.com/searchresults.php?search_simple=true&txtAll=GK+MB115

CJ said:

tale this Ice Power module for an example. power supply and amp all on one small lightweight board, fabulous!

until it breaks,  call the company, they say no schematic, fixing it yourself could burn your house down, please send $87.50 and you are good for another four years.

no wonder they call it ice power, that company is as cold as ice, 

Click to expand...

Indeed, these modules are awfully touchy. No short-circuit protection, no current limiter, they're designed to operate in enclosed systems where no erratic connections can happen, but still, they would blow instantly with a shorted loudspeaker. The only reason manufacturers use them is because they're cheap.
Ther are alternatives, though, but when you want to fix an existing product, there is no substitute. 

metalb00b00 said:

Plugged in the AC power cable again. DC output power LED indicator turned on! and my house circuit breaker tripped!

Click to expand...

So it looks like you don't know avbout the old trick of putting a light bulb (old-style, incandescence) in series with the DUT. If the DUT is shorted, the bulb lights up in full. Else, the bulb will light briefly while the caps are charged and them dim. Indeed, teh bulb must be selected according to the rated power of the DUT.

Any ideas why it happened?

Click to expand...

TOP circuits are quite simple and well-protected. I believe your problem is either a shorted or reversed capacitor or a solder short. Have you replaced the xfmr? It mlay be shorted too.

Yay! I FIXED IT!

https://www.dropbox.com/s/h8yc8jtqwq9kiiw/IMG_20180223_180008.jpg

metalb00b00 said:

Yay! I FIXED IT!

Click to expand...

How?

These are all the parts I replaced.

2A 250v fuse. Reason: Blown.

68uF 400V bulk capacitor. Reason: Dried up. High ESR.

2A 600V bridge rectifier. Reason: Shorted internally.

TOP234YN offline switcher. Reason: Blown.

47uF 25V startup capacitor. Reason:  Dried up. High ESR.

2x 2700uF 6.3V output filter capacitors (for +5V supply). Reason: Bulging. High ESR.

4x 330uF 25V output filter capacitors (for +/-15V supply). Reason: Bulging. High ESR.

metalb00b00 said:

These are all the parts I replaced.

2A 250v fuse. Reason: Blown.

68uF 400V bulk capacitor. Reason: Dried up. High ESR.

2A 600V bridge rectifier. Reason: Shorted internally.

TOP234YN offline switcher. Reason: Blown.

47uF 25V startup capacitor. Reason:  Dried up. High ESR.

2x 2700uF 6.3V output filter capacitors (for +5V supply). Reason: Bulging. High ESR.

4x 330uF 25V output filter capacitors (for +/-15V supply). Reason: Bulging. High ESR.

Click to expand...

Well, you had already changed most of the caps and the TOP, so it looks the last thing that made the fuse blow may have been te bridge rectifier...