So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes? There's no other explanation for it? I'd like to
know before I remove it 'cos it's in the most inaccessible position
imaginable and I may even have to destroy it to remove it without
damaging the PCB traces. Ideally I would have liked to have checked it
out of circuit, but that's not really feasible. But it *must* be blown
anyway, right?

cheers.

On Sun, 9 Sep 2018 13:53:20 -0000 (UTC), Chris
wrote:


So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes?

I can't think of any other reason so gets my vote...

On 09/09/18 14:53, Chris wrote:

So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes? There's no other explanation for it? I'd like to
know before I remove it 'cos it's in the most inaccessible position
imaginable and I may even have to destroy it to remove it without
damaging the PCB traces. Ideally I would have liked to have checked it
out of circuit, but that's not really feasible. But it *must* be blown
anyway, right?

cheers.

If it's gone open-circuit, is there any chance of using power diode(s)
to "bridge" the o/c part(s), rather than risk removing the faulty
component - maybe even using flying leads? It won't look good, but it
might save a lot of work and a damaged pcb.

The other question to ask is /why/ has just that one blown? Is there a
dodgy component further down the line?

--

Jeff

On Sun, 9 Sep 2018 13:53:20 -0000 (UTC), Chris
wrote:


So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes? There's no other explanation for it? I'd like to
know before I remove it 'cos it's in the most inaccessible position
imaginable and I may even have to destroy it to remove it without
damaging the PCB traces. Ideally I would have liked to have checked it
out of circuit, but that's not really feasible. But it *must* be blown
anyway, right?

cheers.

So you have six DC supplies?

Have these a common return?

A Scope would not be my tool of choice for such an investigation.

What was the problem that led to the investigation and what is the
power supply for?

I used to have a problem with bridges years back, but generally if the
bridge went high forward resistance there was more than one internal
diode at fault so the output Voltage generally would be totally
inadequate. I never actually looked at the waveform though :-)

AB

"Chris" wrote in message news


So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes? There's no other explanation for it? I'd like to
know before I remove it 'cos it's in the most inaccessible position
imaginable and I may even have to destroy it to remove it without
damaging the PCB traces. Ideally I would have liked to have checked it
out of circuit, but that's not really feasible. But it *must* be blown
anyway, right?

cheers.

If it's hard to get at, cut it out with snips so not put the pcb at risk -
test each of the 4 diodes fwd/rev and replace it anyway, they are cheap as
chips.


Andrew

In article ,
Andrew Mawson wrote:
"Chris" wrote in message news


So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings
on the secondary LV side of the mains transformer. I'm seeing 100Hz
ripple on all of 'em except one which is showing only 50Hz ripple. Now
that one *has* to be ****ed, yes? There's no other explanation for it?
I'd like to know before I remove it 'cos it's in the most inaccessible
position imaginable and I may even have to destroy it to remove it
without damaging the PCB traces. Ideally I would have liked to have
checked it out of circuit, but that's not really feasible. But it
*must* be blown anyway, right?

cheers.

If it's hard to get at, cut it out with snips so not put the pcb at risk -
test each of the 4 diodes fwd/rev and replace it anyway, they are cheap as
chips.

+1. Never surprises me how many try to get a failed component out in one
piece - at the risk of damaging the PBC.

--
*Husbands should come with instructions

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 9 Sep 2018 16:59:03 +0100, "Andrew Mawson"
wrote:

"Chris" wrote in message news


So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes? There's no other explanation for it? I'd like to
know before I remove it 'cos it's in the most inaccessible position
imaginable and I may even have to destroy it to remove it without
damaging the PCB traces. Ideally I would have liked to have checked it
out of circuit, but that's not really feasible. But it *must* be blown
anyway, right?

cheers.

If it's hard to get at, cut it out with snips so not put the pcb at risk -
test each of the 4 diodes fwd/rev and replace it anyway, they are cheap as
chips.


Andrew
If it's a monolithic bridge it's going to be a little difficult.

There are usually four discrete diodes inside the epoxy, but you would
need a junior hacksaw to separate them.

I have seen a bridge left in and the extra diodes soldered across the
underside of the print, but it isn't the best type of job.

The only saving grace is that the diodes seem to fail open inside the
epoxy and do not seem to end up shorting at a later point in time.

AB

On Sun, 09 Sep 2018 19:31:49 +0100, "Dave Plowman (News)"
wrote:

+1. Never surprises me how many try to get a failed component out in one
piece - at the risk of damaging the PBC.

Make that a possibly failed component, that is readily available and is dirt
cheap to replace.

One of the worst cases is when the board is covered in conformal coating that
has flowed under IC's effectively bonding them to the PCB. So the usual
approach of chopping the pins off next to the package is not enough and it
becomes heat gun and screwdriver leverage time.
--

Certainly sounds rather nasty.
Firstly though might need to know what drove one leg to destruction?
Also be very mindful of any electrolytic capacitors on that supply this
sort of thing can spell doom.

Also on an amp inside a sub woofer the bridge was just not high enough spec
as it did not take account of the large current on charging the capacitors
at switch on and eventually died.
Brian
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Chris" wrote in message
news

So I'm scoping the power rails on this piece of kit I'm working on. It
has 6 monolithic bridge rectifiers wired directly to various tappings on
the secondary LV side of the mains transformer. I'm seeing 100Hz ripple
on all of 'em except one which is showing only 50Hz ripple. Now that one
*has* to be ****ed, yes? There's no other explanation for it? I'd like to
know before I remove it 'cos it's in the most inaccessible position
imaginable and I may even have to destroy it to remove it without
damaging the PCB traces. Ideally I would have liked to have checked it
out of circuit, but that's not really feasible. But it *must* be blown
anyway, right?

cheers.

On Mon, 10 Sep 2018 08:00:26 +0100, Brian Gaff wrote:

Certainly sounds rather nasty.
Firstly though might need to know what drove one leg to destruction?
Also be very mindful of any electrolytic capacitors on that supply this
sort of thing can spell doom.

Yup, looks like the large storage cap for that rectifier went leaky and
probably drew enough current to damage it. For sure that large cap was
****ed a priori.