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Topic: Blown Caps in 0-30v 0-10a bench supply repair (Read 5227 times) previous topic - next topic

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.

smeezekitty


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.
Avoid throwing electronics out as you or someone else might need them for parts or use.
Solid state rectifiers are the only REAL rectifiers.
Resistors for LEDS!

Suaveman

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.

dhenry


Suaveman

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-

http://www.eevblog.com/forum/reviews/beware-yihua-yh-305d-bench-psu/

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-


dc42

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.
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MAS3

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.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

dhenry

Quote
these are pos units.


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

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.

smeezekitty



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.
Avoid throwing electronics out as you or someone else might need them for parts or use.
Solid state rectifiers are the only REAL rectifiers.
Resistors for LEDS!

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