Testing two TO220 recifiers...

Hi again,

Sorry about the typo...

Here is what they are reading with the DMM on diode tester:

(negative lead on center pin)

SB1040: 0.201 on both outer pins.

SB1640: 0.169 on left outer pin, 0.170 on outer right pin.

(positive lead on center pin) all readings are infinity.

-Landon

Sounds like they're working fine.

Agreed. They will be Schottky barrier types, which read way different from 'standard' silicon types. From the symptoms quoted, the most likely bet would be a small electrolytic on the primary side gone high ESR, but also could be many other things, including resistors gone high. Unless there is a particular issue regarding size or physical shape, I wouldn't bother going any further than you already have. These PSU's are so cheap now as genereric replacements, they don't warrant the labour to fix them. It's also a good opportunity to up its rating for the same money.

Arfa

On Sun, 10 Dec 2006 18:41:50 -0800, lj_robins Has Frothed:

It will probably cost you nearly as much in time and effort to repair the supply as it would to buy a new one. My guess is you have a dry electrolytic somewhere but without the proper meter to test them it will be trial and error to find. But hey if you have the time, who am I to discourage you? It is very rewarding especially for a newbie to revive things like this. Just be carefull though.

Hi,

Thanks to those that have so far replied.

I figured that those two Schottky rectifiers were fine the way they were testing, the numbers just didn't make any sense.

If I were paying my own technician to diagnose this the supply would have already been replaced and the computer would have been out the door and back to the customer. But every ATX supply that has died in this house acts exactly the same way (gives the ziiiiit and has low output voltage) and I'm kind of curious as to what is dying on the circuit boards.

One supply that was iffy about whether or not it would stay on depended on how much was hooked up to it, that ended up being a very obviously bulged filter capacitor on the output side. I replaced it with one that was double the voltage rating of the old capacitor, two years later that supply is still running and ended up being a 60 cent (US) fix.

But, back to the point, I probably will just replace the supply.

Thanks again.

-Landon

On Mon, 11 Dec 2006 05:11:55 -0800, lj_robins Has Frothed:

From what I recall what you are hearing is a somewhat common death knell for failing switch mode supplies and I have heard it myself.

Best bet.

It's almost always electrolytic capacitors. They dry out internally and the ESR goes way up, eventually the voltages sag and get noisy and then when it gets bad enough, it won't power up at all.