Dual output supply dead

Circuit sounds about right, though there will likely be overcurrent protection as well. As far as repair goes, just bin it, theyre often sods to do.

NT

Check the fuse? :)

Might also be as simple as an open startup resistor.

But as someone else suggested, may not be worth the trouble. For now, if you need to get your system back up, move the drives to another enclosure. Then, later if you want a challenge, try to repair it.

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Nope on both counts. When I removed it from the enclosure, I made the mistake of picking it up a short time later and sitting down on the couch to have a look at it.

Quite annoying to get "bit" from a small device with no wires attached! (of course, the input filter was still charged :< )

Unfortunately, this enclosure handles *3* half height drives (instead of the one or two typically supported) so I have to look for a more creative packaging option.

Or, leave the replacement supply sitting atop this enclosure until I find something else, suitable.

You can't say " nope " for the contention of open startup resistor, as the main primary filter cap remaining charged ( often for hours ) is a totally typical symptom of this failure. Couple of quick checks would be to follow the print from the " + " terminal of the primary filter cap, and see if a high-ish value resistor is hooked to it on its way to one of the chopper tranny pins. Another possibility which is very common on all switchers, and will also leave the main filter cap charged due to the chopper oscillator not running, is defective primary-side electrolytics. Look for any small electros, particularly if they are positioned close to the heatsink or anything else that gets hot, and ESR them. If you haven't got an ESR meter, just replace them. It's worth going that far, but beyond that, commit it to landfill ...

Arfa

I repeat, "Nope". :> The fuse is known good (since the input filter would never charge through an open fuse).

And, this topology does not employ the sort of startup resistor you are expecting. I.e. there is no DC path to the SMPS controller's "power" pin from the input filter. (I assume you are expecting a ~1W dropping resistor between the input filter and the SMPS controller)

To be precise, there are exactly 5 connections to the input filter:

- the input filter cap's + terminal

- the bridge's '+' output terminal

- one side of the transformer primary

- one side of an RC snubber across the xformer primary (which is *two* components/connections) in series with catch diode

I'll drag out a DVM and verify power is available at the SMPS controller, though...

Aside from the input filter (180uF 400VDC) and secondary output filters, there are exactly two electrolytics in the design. The first serves as a filter on the sense/feedback coil. I haven't yet tracked down the role of the second...

This looks tiny enough that I can probably trace the circuit topology in half an hour. I'll photocopy the foils and see how quick i can reconstruct the basic design...

I assume you checked ALL solder connections for bad joints? And put your meter on all higher current film resistors and compared the measured value to the color code?

Bob

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ok question. we may have to step up a notch now.

What kind of SMPS controller does it have? is the controller and chopper transistor seperate, or is it an all-in-one such as a VIPIR or STR regulator. those are notorious for dying out.

3842 driving a discrete FET (can't see the P/N on the FET since it is hiding behind the input filter).

And, to answer "Bob's" questions, below (his post hasn't made it to my news server):

- first thing I did was reflow all the solder joints (since it is so easy to do and I've seen problems with fatigue in the past)

- there are only two "higher current" (wattage) resistors on the board: one in the snubber and the other in the current sense leg. The current sense R was verified as "approximately the right value"; the snubber was ignored.

I made a photocopy of the foil patterns last night and will trace it out this evening if I have time. In the late evening quiet, I also was able to notice a "ticking" sound -- as if the switcher was starting up and then shutting down again. I'll pay closer attention to the current sense circuit when I am tracing the foil patterns tonight -- along with the OVP shutdown (as those are the two things that come to mind that could cause this cyclic start-shutdown behaviour).

But, tomorrow brings another surplus equipment auction so I may stumble on a suitable replacement and just pitch this... :-/

If it uses a 3842 / FET circuit, then it just abiut *must* have a startup resistor and supply pin decoupling cap somewhere, otherwise, how does it get a supply to the IC to start it up ? If it's ticking, my money is still on a cap ...

Arfa

Trust me, I can eyeball a 1.5" length of foil with 5 holes in it! :>

As I said in a previous post, only two R's larger than 1/10W: one as the current sense R; the other as the snubber (it's REALLY easy to see an RC-D across the primary ... you don't even have to look hard! :> )

My first guess would be the current sense resistor being open and immediately shutting the controller down. But, I haven't yet traced the foils to see what else is going on.

Did you get to the bottom of it yet, Don ? I'm always interested in SMPS faults as I do a lot of work with them, and any info that saves a few minutes, is extra money in the bank ...

Arfa