Mastech HY5020E 50v 20a Bench Supply: Economical to repair?

[Seekonk]

Send me your old caps! I'd be perfectly happy using them.  I'm pretty amazed at how expensive even crap ones are from China. Doesn't matter if some of the shrink is burnt off.  If you were happy before, they aren't an issue. 

[richfiles]

I would actually like to get one of those component/ESR testers. I know they're pretty much just a micro with and LCD running a testing program. I think it'd be useful to have around, and they are pretty dirt cheap too. Every gut instinct tells me the caps are just fine. I just have not tested the ESR yet. I feel like it's probably gonna be fine, but I just don't know yet. This puppy went bang pretty hard.

And you're right... those caps can get spendy! I normally spam part replacements, just to be on the safe side. If I think a part was even slightly stressed, I prefer to replace it. When you have 4 parts that cost $4-7 each... The cost adds up quick, though. As long as they test okay though, i'm gonna reuse them, I think. At least for testing anyway.

[bitseeker]

An ESR meter is definitely a good thing to have. If you have an oscilloscope and function generator and don't mind a little math, you can still measure ESR.

[richfiles]

Haha! I already have THAT video up on another tab! I just haven't had the time to do anything. Probably won't have time for about 2 weeks, due to work. I'll have to clear my workbench for my current order...

But yeah, definitely looking at getting one of those cheap combo component testers. At the price, why not. Looking at http://www.ebay.com/itm/2016-EZM328-transistor-tester-ESR-table-frequency-meter-square-wave-genera-/172129915560 at the moment. Seems to be latest rev, with socketed micro (good for testing flashed rev updates).

[bitseeker]

Yeah, real life has a way of taking over. I haven't seen that particular version of tester. It seems to have most of the right stuff (encoder, socketed uC, plug for leads). I couldn't tell if it has input protection. I wonder what the little trimmer pot is for. Screen brightness? Anyway, that'd be a discussion for https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/

Looking forward to seeing how the rest of this supply turns out when you're back from your income-generating project(s).

[MrSlack]

Watch out for the cheap Chinese "transistor tester" units. They don't seem to consistently measure capacitor ESR. I've had readings that vary by as much as 200% in successive measurements even if I thoroughly discharge the caps between each reading.

I opted in the end to purchase an ancient LCR bridge. That is incredibly consistent, plus it does inductor Q which is nice. Cost about the same on ebay as a higher end transistor tester. Uses the same method w2aew uses to calculate the ESR as well wrapped in a bridge.

[Shock]

Probably worth a punt for a $10 or so Chinese meter with free shipping though, mine seem to take reproducible measurements but I've hardly put them though a workout.

I agree sinking some cash into a decent LCR meter is worthwhile in the long run. Multiple frequency support and a wide capacitance range is important as well, as you can be comparing apples and oranges if you're not testing to the frequency on the datasheet. So the DER EE DE-5000 is another option.

Some decent caps can self heal or reform unless they are too far gone, like leaking electrolyte or bulging. After a time sitting idle, depending on when you are testing them in their life cycle this can throw out results.

I've seen SMPS caps or ones placed next to warm heatsinks (especially the cheap brands) their life expectancy seems to be under 3 years for partial or total failure. Heavy hours or really poor design I'd give them a year tops.

[MrSlack]

I've got 55 years out of some Sprague ones so YMMV

[bitseeker]

@richfiles: Any news on your Mastech?

[richfiles]

No new news... Hours have picked up at work, and I've just not sat down with it. What free time i have, has been applied to other projects, like my Kerbal Space Program controller.

Don't worry! I haven't forgotten about this thing.

[bitseeker]

No worries. Just thought I'd check when I saw an online mention of one of these supplies. It sounded familiar and a quick search brought me back here.

I haven't played KSP (though I've spent a good number of hours in Orbiter a number of years ago). Your controller project sounds intriguing. I'll have to check it out.

[bitseeker]

I ran across this schematic of the HY5020E from an older thread around here that was actually about the HY3040E. This schematic and the PDF posted earlier in this thread are very similar to each other except on this one,

1. The output is actually labeled 50V instead of 30V despite both being titled "Diagram for HY5020E"
2. Changes to PCB HY023 (top of the schematic)

[richfiles]

Hey, thanks! Always good to seek moar information!

[bitseeker]

I'll second that.