Re: Bad wiring - No. 2?
- From: Seum <Seum@xxxxxxxxxxx>
- Date: Wed, 01 Jun 2011 21:21:32 +0100
Seum wrote:edfair wrote:Your cart wheels were inductors with ferrite cores.
The metal stuff was heat sync to remove heat from the switching
transistors that were mounted to them somewhere, probably near the
The pop was probably one of the switching transistors. If so, it may,
or may not have done any outside damage.
Yeah, brushing against a loaded component can get your attention. I
picked up a Xerox 820 supply with a blown bleeder and partially
discharged the supply through the palm of my hand. Still hurts to
Many thanks to Paul, L.M.& C, and Edfair. I'll send my first attempt now and will read your emails today.
This morning I took the cover off the PSU and made a few measurements (for what they are worth. :-) )
With the cover off I found a small 1.75" square circuit board just inside the external socket. This little board has 3 connection wires, one to ground and the other two to the mainboard. I made 3 resistance measurements on those 3 wires from the prongs of the socket to the case (the ground) and from the two other connections on the mainboard.
Resistance between the ground pin in socket and the ground pin on the PSU - 0 Ω.
Resistance between the N(eutral) pin and the connection to the mainboard: 0 Ω.
Resistance between the L(ive) pin and the connection to the mainboard:
- Infinity Ω.
Is it possible that something blew on that little circuit board? It has a piece of metal box that passes through the rear wall of the box and the socket has a plastic piece that is fixed to the rear wall of the box
with 2 screws. I took them out and tried to pull off the plastic piece in an effort to get the circuit board out of the box to see if there are any damaged components on it. The I-0 switch is near the socket and is firmly glued into the little circuit board.
Now back to your writings :-)
Thanks for the help.
There is a review article for your PSU here.
And a picture here.
I think I'm seeing a black, heat-shrink wrapped fuse, on the
main board. The little board with the AC socket on it, could
contain a few filter components.
If we use this as a reference, the little filter board could
contain the stuff up to "C2" and "C3". The bridge
rectifier is more likely to be on the main board, but
I can't see it in the picture. The equivalent of C2
and C3, could be the blue capacitors on the tiny AC socket
Then the question becomes, what series-connected components
are in the path. The Pavouk diagram has NTCR1, which is the
inrush limiter. I doubt they use something so crude on modern
supplies (mainly because they're a reliability issue).
It's possible that any Active PFC circuit, may have the side
benefit of making it possible to limit inrush current. I've never
looked at a datasheet for an Active PFC, so can't really tell you
whether that is the case or not. An Active PFC circuit didn't
exist at the time the Pavouk site owner traced his power supply.
Hmmm. Well, this isn't going to do it. The Active PFC is a parallel
And according to the text description for that block, the resistor
near the right of the diagram, is the inrush limiter (equivalent
of NTCR1 in the Pavouk diagram). So the Active PFC itself isn't
moderating the current enough, and the circuit is still provided with
a negative temperature coefficient resistor (resistance drops when
it gets hot, after a couple seconds of operation).
If that is a fuse on the main board, then some series connected thing
opened on the socket board. Make sure, when you're doing the ohm
tests, that the switch on the back of the power supply is in the
ON position, as otherwise, the open thing could be the switch itself.
When it comes to "magnetics failures", such as T1 or T5 on the
Pavouk diagram, typically that happens because of cold solder
joints. Some magnetics, consist of enamel wire which has been
stripped chemically. And due to lax quality control, the
device doesn't get soldered into its PCB properly. I've had a
few items like that in my lifetime, that needed to be re-soldered.
But no failures inside a power supply. This was with other electronics.
Good luck and be careful,
Thaaaank you Paul. You are truly a mine of information :-)
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