Repairing PSU - what's the black plastic cylinder on the cable?

[Lobster]

I've just dug out our portable DVD player and found that there's a problem with the PSU unit - it's a 12V wallwart job with a welded 3.5mm coax plug, and like so many of these items, has a solid black plastic cylinder encasing the wires, just upstream of the plug.

The problem is an obvious loose connection in either the plug or within the 'cylinder'. Ordinarily I would just chop off the plug and replace it with a soldered one, but what is the cylinder for? Are there connections inside it which may be affected? Can I just do without it? Even if it's not ideal, can I do a temporary repair with no 'cylinder' if need be, as I need to sort this out today.

Thanks David

[Andrew Gabriel]

The 'cylinder' is just a ferrite core with the cable passing right through. It's there to stop the cable acting as an aerial, transmitting RF which might get into the cable at whichever end it's fitted. It will work fine without it, although a nearby radio might not:-( You can buy them to refit (it's difficult, although not always impossible to reuse one of the original ones).

[andy]

The cylinder is almost certainly a ferrite core to suppress interference traveling along the cable. it will work without this and in my experience you are unlikely to notice the difference.

A.

[meow2222]

a ferrite core, as said. Most unlikely that running an iron lump wallwart without one would ever cause a problem.

NT

[Lobster]

Ah OK, thanks.

So apart from the fact that it's not a vital component, there aren't going to be any connections (ie possibly loose) within it anyway?

David

[Dave Plowman (News)]

No - they are fixed round the *outside* of the cable. Some aftermarket ones clip in place. Most as supplied are moulded on.

[Clint Sharp]

In message , [e-mail] writes

It's *highly* unlikely to be an 'iron lump' wall wart, it's almost certain to be a switch mode and the ferrite works both ways, it stops RF generated in the DVD player from potentially causing problems too.

[T i m]

When dealing with this sort of problem in the past I've cut the wires off close to the ferrite at the wall wart side and used whatever was sticking out the output side to pull the cores through. The outer sheath may be persuaded to release with the aid of a thin flat screwdriver (carefully, down onto a firm surface) between the cable sheath and the ferrite or failing that, just run a suitable series of drills through it.

Once clear remember to thread it back on the cable BEFORE you solder the o/p plug on (as it will never go as well the second time?) and then tack it in place with a drop of EvoStick.

Jobs a goodun. ;-)

T i m

[meow2222]

Its a wallwart for a dvd player, so I dont know what you base that on. There are plenty of both types in use.

Anyway, the OP can safely ignore its existance.

NT

[Clint Sharp]

In message , [e-mail] writes

The ferrite on the power cable is a bit of a give away.

The power requirements of portable DVD players make a switch mode *much* more economical to manufacture and ship than a 'lump of iron' type PSU.

Agreed 100%.

[meow2222]

You may be right. I've got kit of similar power with iron supplies though, and ferrite beads on.

NT

[Dave Liquorice]

Ferrites at the appliance end is to st^H^Hreduce the RF shit coming out of the device being radiated by the power wires.

[meow2222]

Yes, which is a) rarely a problem b) massively reduced by the fact that most such rf is going down each conductor in opposite directions.

NT

[Andrew Gabriel]

Actually, it's really hard to make computer based kit meet EU EMC regs.

That RF isn't a problem. It's the common mode RF which is treating the lead as an antenna which is the problem, and difficult to get rid of, and is orders of magnitude higher frequencies. That's what the ferrite bead is for. It looks like a high value resistor to such RF.