Problem with my SPX90

[Ike Zimbel]

No worries...it's been my experience that you can't go wrong by rocking!
iz

[LeeYoo]

Read the other SPX90 post.

[swin]

Are three L6,L5,L4 caps? and if not what are they ? my L6 is totally burnt and it seems the other caps are not leaking and ok....any rate no power ...little help
thanks

[LeeYoo]

Hi
L4, L5, and L6 are inductors, to remove any high frequency ripple left on C19, C21 and C23.
If L6 is totally burned, but still has continuity, the supply would still work, but with a slightly higher ripple on the +5 rail. Non critical component.
You could replace with any inductor of the same size or bigger that can handle the current of the +5 rail. Or even with a wire link, at the cost of slightly higher ripple.
Leo..

[jumunius]

Hi, so although I earlier boasted of fixing 4 of these, one of them did not last. Turns out couple solders are cold/broken due to some sort of leakage/corrosion. One of the problem solders is on a 20uH choke and I'm having trouble even desoldering the component because of all the crap around it. Ultimately, I may need to replace the choke because I'm not sure the leg will survive the removal. I think I found the appropriate part at my local electronics store, but I am not sure since it *looks* completely different.

The existing part is L6, one of those dark green cylinders in the pics earlier in this thread. The only marking on it is 200k, which I take to mean 20uH (consistent with the schematic), 10% tolerance.

The part I have is packaged as "RF CHOKE 22uH, Q 50 MIN, 410 mA DC". It looks like a resistor and it has red-red-black-gold bands.

So, is there a problem with using a different construction of choke? And is the amperage or other ratings a problem?

PS. I was following this thread but completely missed LeeYoo's post... until now. As I'd rather not have the ripple, my question still stands as to whether or not this component will work.

[acreil]

I suspect it should be ok, if the current rating is adequate. It's supposed to be an RF choke (i.e. attenuating high frequencies), so that's what you want.

[LeeYoo]

Those series chokes come in different shapes and sizes.
Two things are important. The value (in uH), and the DC resistance.
The value has to be about right ofcourse (and slightly more is better).
And the DC resistance as low as possible, to handle the current draw.
Higher DC resistance is more heat, and lower resistance is a bigger body that might not fit.
Leo..

[jumunius]

Originally Posted by LeeYoo

Those series chokes come in different shapes and sizes.
Two things are important. The value (in uH), and the DC resistance.
The value has to be about right ofcourse (and slightly more is better).
And the DC resistance as low as possible, to handle the current draw.
Higher DC resistance is more heat, and lower resistance is a bigger body that might not fit.
Leo..

Thanks. The packaging doesn't make resistance value clear unfortunately.

So as I'm unclear about the current usage of the +5 rail, maybe I ought to test the draw? Or would it be too daft to simply replace the part and feel whether it overheats upon being on for a few minutes?

And curiously, how does the use of a choke differ from a ferrite bead? Don't they serve the same purpose, i.e. HF attenuation?

[LeeYoo]

Don't stress too much about value and size. This is not critical here.
You just want a low resistance to reduce the heat. If the packaging is the same or larger, it's fine.
If unsure, measure resistance with a DMM. I would expect less than 1ohm.
Just a ferrite bead would not be enough to get the 20uH. A coil with several windings on some ferrite core is normally used.
Leo..