Blown Caps in 0-30v 0-10a bench supply repair

My best guess, replace the caps and see what happens. If it still does not work, replace IC1 & IC2, Standard opamps, and they have been nice to put them in sockets. I do not believe the 2N3055 is broken by that stunt.

// Per.

Go to radioshack and get a couple of those caps. Solder them in and turn on the power supply.

If it works, great.

If not, throw away the guts and reuse the case.

jackrae:
With all due respect, since you seem to be somewhat lacking in knowledge on what a power output transistor looks like, then your chances of identifying the problem are pretty low. Without a circuit dagram, someone who really knows what they are looking for will have to dig deep into their knowledge of circuitry to identify where the faults lie. As previously stated, your best bet is to simply replace the damaged capacitors, switch ON and if it works, all well and good. If it doesn't work, and you really want to keep it, then pass it onto a colleague who has the skills to trouble shoot. Otherwise you could well be throwing good money after bad, with little chance of success.

This sounds like good advice. I don't have much skills in circitry, but can test componenets and understand the basic principles behind the supply. I taught myself alot about dc electronics, and am just wading into learning how circuits work, so this may be beyond my skill level. I ordered some quality caps, ~5 or so of each (35v, 50v 470uf), i don't much care for radioshack, and would rather give an ebay seller my business, but regardless. They should be here in a few days.

If the caps/shorted lead patch/solder joint fix the problem, then huzzah. If the transistors are bad, i can replace those if necessary as well, so long as the repair costs are under $25 total. I'll have someone with a proper electronics education take a look at it (my father) after i replace the caps, fix the trace, and replace any transistors/diodes that may have been damaged, before powering it up again for saftey reasons. If he says scrap it for parts, thats going to be the gameplan unfortunately, he's fairly well educated in the matter, though has not worked in the field for almost a decade now. Still, he might be able to show me how/what failed, and if its repairable. Busy week with lots of snow in norcal, so it might be a few days before he has some time to take a look at it though.

Might make a nice vlra battery case you could stuff a charger in hooked up to a solar panel if its unrepairable. And i'm sure theres plenty of undamaged components i can scrap for future projects so its not all bad.

Its also relevant to know, it did not pop, and die immediately. The voltage/current display remained lit, but the loud cap pops and smoke made me disconnect everything as quickly as possible. I have not powered it up since then. i'll wait for the caps and trace/fix before plugging it in again.

Live and learn i guess. Should have just spend a bit more on a mastech. Don't buy these knockoff pos's. Its like 50-75$ more for something quality and protected against stupid mistakes like reverse polarity connection of a fla.

Should have just spend a bit more on a mastech. Don't buy these knockoff pos's. Its like 50-75$ more for something quality and protected against stupid mistakes like reverse polarity connection of a fla.

It is not clear why it blew. It could be just due to poor design or poor quality.

true, true.

The transistors tested ok, so i'm just waiting for the new caps to see if thats going to fix it. The cap's in question, i'e heard nothing good about, so quality issues definately could have been the cause of failure just going off that.

Or the caps could have been from that bad batch made with the stolen seret suace electrolyte formula from a few years back. Nothing is certain, other than the quality of this supply fits in line for what i paid for it. Lesson learned.

Suaveman:
true, true.

The transistors tested ok, so i'm just waiting for the new caps to see if thats going to fix it. The cap's in question, i'e heard nothing good about, so quality issues definately could have been the cause of failure just going off that.

No.

Suaveman:
Or the caps could have been from that bad batch made with the stolen seret suace electrolyte formula from a few years back. Nothing is certain, other than the quality of this supply fits in line for what i paid for it. Lesson learned.

No.

Suaveman:
Those caps do not just blow up out of the blue. You connected your battery backwards, and that blew them. Get over it, it has nothing to do with "cheap" capacitors. Even Nippon Chemicon's or ELNA won't tolerate that kind of abuse!

// Per.

^^

Well yeah, your probably right. Though i cannot be certain it was connected with reverse polarity. The fact remains the cap quality has been said to be very poor for said brand. In all likely hood it was a reverse polarity stupid mistake, i was just commenting that the caps in this supply have been known to be crap quality. So don't buy the model i did.

I'll concede it was almost certainly reverse polarity that blew them, but the fact remains you get what you pay for, and when you buy the cheapest possible option, issues like this are common. Not to say the caps would have blown under normal use, just that they don't have a good rep. Perhaps they would have lasted, assuming i did not make the mistake i did, perhaps they would fail due to poor quality.

The point, is that while it was most likely my mistake that blew them, and any cap would blow in that scenario, they used poor quality components in this supply, and i got what i paid for.

In any case, the replacement caps arrived, and i'll be installing them once i have someone (my father) with a background in electronics take a look at it first. I'll update as to if the repair was sucessful or not when we have some time to take a look at it together. Forgive my rudimentary understanding of electronic circuits, and assumptions it was the low quality components and not user error that caused the failure. The fact remains though, the caps are known to be poor quality.

Caps were replaced and shorts were soldered and epoxy'd over. Checked pos/neg out for a short, and sure enough it beeped at me. I'll tear it apart and start checking diodes, but at this point, i'd considering buying a new one, or looking into building one, with some bad-ass protection circuitry (diodes, fuzes, etc). Too late now to do any more work on the supply.

BTW, it wasn't plugged in when tested for shorts, and tested positive for shorts between the +/- outputs both with the power switch on/off. Does not powering it up have anything to do with it showing a short?

Checked pos/neg out for a short, and sure enough it beeped at me.

Depending on how you measured it, that can be "caused" by the capacitor.

It was just a simple diode/short test, what would be the proper way to test it?

Check the resistance between the terminals?

Use your resistance ranges and measure it over a long period of time. For short bursts of tests, a capacitor appears to be short.

dhenry:
Use your resistance ranges and measure it over a long period of time. For short bursts of tests, a capacitor appears to be short.

Agreed. Personally I would just go for it and fire it up.

Alright sounds like a plan. I have some time to tear it apart again and test any diodes that may have been fried w/ the reverse connection, so i think i'll do that and if all is well, fire it up and hope for the best.

Yeah. You have nothing to lose.

Ok, so where the positive output is soldered to the board, there is a diode soldered to the same joint, inbetween the replaced cap, and the two white (resistors?).

It shorts both ways, but do i need to take it out of the board to test it? Or can you test a diode in circuit (used both my diode test, and ohmic resisitance functon on my multi, no resistance either way). Also, a resistor, right next to that diode/cap, 1k ohm, is shorted, looks like its burned up, and shows no resistance when measured with a multi.

And i finally found a bit more info, and the brand name for this supply-

From what that thread is saying, these are pos units. If i have spare resistor/diodes of the same rating laying around, i may attempt to replace them, but i'm not spending any more money trying to fix something thats, well, a piece of crap.

Anyway, i'll dig around and see if i can find the resistor/diode needed, i'll update if i can find what i need.

Heres some pics of the diode/resistor-

The 1K resistor looks OK to me, it may be connected in parallel with the diode.

If the diode reads close to zero ohms both ways round using the lowest resistance range of your multimeter, then either it or a capacitor connected in parallel with it is probably shorted. I would unsolder it - should be easy, it's a single-sided PCB - and test it again.

If you are beeping for shorts, always remember how that works.
Most multimeters i have seen yet, beep upon a resistance of 1K or lower.
This means that beeping is more like detecting low resistance than really looking for shorts.
A low resistance could mean a short / defect, but could also mean it's designed that way.

So beeping will give you some idea as to where to look for a short, but will require you to do some closer investigation as to whether you just found a short, or a feature.
You can do this by checking the resistance, eventually taking one side of the component out of the board so you are sure other components have no influence to your test.
Beeping / diode testing probably gives you a reading (millivoltage) on your display, which depends of the type of diode you are testing .
You cannot make any consequenses out of your test if you don't know what the result with that specific part is supposed to be.
So you could ask here what results to expect, stating the exact component type you will be testing.
Or look it up in the component's datasheet.

these are pos units.

Tell that to those folks who insisted on reverse polarity on your battery, :slight_smile:

For powering up those unit, the typical approach is to put a light bulb in serial. If the light bulb glows, you have a problem.

dhenry:
For powering up those unit, the typical approach is to put a light bulb in serial. If the light bulb glows, you have a problem.

I was just about to suggest this. It is called a dim bulb device and I use it all the time for powering up antique and questionable electronics. You can start with a low bulb and slowly go higher.

A small glow should be ok. Lighting up brightly indicates a short.