what component is this and how to test ?

[angellonewolf]

just a quicky i hope ive picked up a non working dc power supply keeps blowing the fuse
when i replace the fuse and power on there is a flash right where my finger is but there is no space to see if its the capactors or the black oblong component now i know i need to remove the capactors (im not at home so got no solding iron) but like to get a head start on fixing

any ideas what it is and can i test it with out removing it

and if its gone bust is a component that blows on its own or a component that blows because theres some thing wrong with the curcit ?

 

[Dcal]

The thing your finger is on is a bridge rectifier and very likely to give the problem you describe.
Having said that I know very little about electronics.

 

[ajlelectronics]

Is the fuse black inside? That would tell me that the chopper transistor is short circuit. The bridge rectifier is probably objecting to the short circuit current, so will also need to be replaced. Depending on the age of the board, I would also be swapping out electrolytic capacitors, particularly if any of them look bulged on the top.

 

[eddie49]

Dcal is right, that rectangular component with the oblique corner cut away is a bridge rectifier. It has four diodes, 2 x AC inputs, plus & minus out, probably feeds the tall black capacitors, possibly with 325v DC. You would need to remove it from the board to test it. The flash that you see may be because one of the pins, or the PCB track, is burnt away.
However, you're also right that the rectifier is maybe just a symptom, the original cause is more likely to be a short-circuit in the MOSFET transistor(s) that run this switch-mode power supply.

 

[angellonewolf]

 

[angellonewolf]

added a full pic of the board when home tonight will desolder the components and have a test see what comes up

 

[minimutly]

I agree, rectifiers rarely fail, even when overloaded they take a while to heat up to cook level. A dead short elsewhere would kill it though. This is not a 2 minute fix.

 

[ajlelectronics]

The choppers are attached to that heatsink, either side of the temperature switch. There may be some associated diodes too that will want looking at. It's not a "swap the fuse and hope for the best" job. ;-)

 

[angellonewolf]

Ok perhaps I should have looked be for i leaped

try taking a components off a board that double sided with no heat station that you lent out 2 weeks ago and still not had it back

 

[angellonewolf]

I've damaged the track but can get round it by looping a wire but need to know where to go from here

 

[skotl]

Oooft. Yeah, that's goosed!

Minimutley suggested that rectifiers rarely fail but I have had the opposite experience - for me, diodes and rectifiers seem to be the most common cause of failure on a board.
Sadly, they also tend to fail short circuit too, taking out anything else in the vicinity.

 

[angellonewolf]

its bad i agree but as the legs only need to be conected i can wrap a wire round to make the cuircit so it workable but i need to see if its the fault or its more in the cuircit not just this item blowing

 

[skotl]

its bad i agree but as the legs only need to be conected i can wrap a wire round to make the cuircit so it workable but i need to see if its the fault or its more in the cuircit not just this item blowing

Oh sure- that's not what I meant. I meant that the bridge is stuffed!

Should be a relatively easy fix, but then the next question will be whether there are any more casualties on the board...

 

[eddie49]

The rectifier should be marked with two squiggles for the AC input pins, and + and - for the DC output With a meter on the Diode Test range you should see infinite resistance - no conduction - one way ( indicated by "1." ), for each of the four diodes, and conduction ( indicated by "0.7" or similar ) the other way, four times. Any short-circuit will show as 0.0
Was any pin already loose or burned, which would explain the flash you saw?
I would check resistance on the board, across the tracks where the + and - of the rectifier used to be. The reading may fluctuate as the capacitors charge, but it must not be near zero Ohms ( which would indicate one or more of the MOSFETs is shorted ).

 

[angellonewolf]

Oh sure- that's not what I meant. I meant that the bridge is stuffed!

Should be a relatively easy fix, but then the next question will be whether there are any more casualties on the board...

The rectifier should be marked with two squiggles for the AC input pins, and + and - for the DC output With a meter on the Diode Test range you should see infinite resistance - no conduction - one way ( indicated by "1." ), for each of the four diodes, and conduction ( indicated by "0.7" or similar ) the other way, four times. Any short-circuit will show as 0.0
Was any pin already loose or burned, which would explain the flash you saw?
I would check resistance on the board, across the tracks where the + and - of the rectifier used to be. The reading may fluctuate as the capacitors charge, but it must not be near zero Ohms ( which would indicate one or more of the MOSFETs is shorted ).

 

[angellonewolf]

 

[angellonewolf]

test results showing it good ?

 

[eddie49]

Those readings look OK, and almost confirm that the rectifier is good. There's just a couple more tests to perform:
There are four diodes in a bridge rectifier, and each one has to be tested two ways, a total of 8 tests. You have 6 results, so two more tests have to be done. There are two diode forward-conduction values, 0.57 and 0.58; the other two diodes also have to be checked for forward conduction. If they were both open-circuit, the fuse would not be blowing, and if they were short-circuit, the reverse blocking tests would have failed, but anyway, for completeness:
The last two tests are:
Red meter lead on "-", black meter lead on the first AC pin from the left.
Red meter lead on the second AC pin from the left, black meter lead on "+".

Both of these tests should show a forward voltage drop of about 0.5v to 0.6v, and will confirm that all four diodes can conduct.
Then check resistance on the board, across the tracks where the + and - of the rectifier used to be, as described in post #14. The rectifier does not need to be reinstalled to do this test. There may be an initial low indication, as the capacitors charge, but if it remains low, or zero Ohms, then it would indicate that, as suspected, one or more of the power transistors on the heatsinks are shorted.

 

[angellonewolf]

Those readings look OK, and almost confirm that the rectifier is good. There's just a couple more tests to perform:
There are four diodes in a bridge rectifier, and each one has to be tested two ways, a total of 8 tests. You have 6 results, so two more tests have to be done. There are two diode forward-conduction values, 0.57 and 0.58; the other two diodes also have to be checked for forward conduction. If they were both open-circuit, the fuse would not be blowing, and if they were short-circuit, the reverse blocking tests would have failed, but anyway, for completeness:
The last two tests are:
Red meter lead on "-", black meter lead on the first AC pin from the left.
Red meter lead on the second AC pin from the left, black meter lead on "+".

Both of these tests should show a forward voltage drop of about 0.5v to 0.6v, and will confirm that all four diodes can conduct.
Then check resistance on the board, across the tracks where the + and - of the rectifier used to be, as described in post #14. The rectifier does not need to be reinstalled to do this test. There may be an initial low indication, as the capacitors charge, but if it remains low, or zero Ohms, then it would indicate that, as suspected, one or more of the power transistors on the heatsinks are shorted.

 

[eddie49]

Counting from the left, the four pins are: "+", first AC pin, second AC pin, "-" .

The results shown above are measurements across "+" and "-" , in both directions. One of the results, with + ( i.e. Red meter lead ) on "-" and - ( Black meter lead ) on "+" shows 1.13, which is the forward-conduction value across two diodes in series.

The last two tests requested were
1. Red meter lead on "-", black meter lead on the first AC pin from the left.
2. Red meter lead on the second AC pin from the left, black meter lead on "+".

Test 1 has effectively been done, by conducting through two diodes to the "+" pin.

I'm fairly confident that the rectifier is OK, but some other component is shorted and causing the fuse to blow.