VOGONS


First post, by appiah4

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I acquired a Socket 7 motherboard not long ago.. Aside from a few missing capacitors, it also has a broken coil choke. It seems to me a ferrite bead of 12mm external 8mm diameter with a 12 loop copper coil around it..

I don't know how to determine (or guesstimate) the rating of this part, where to source it, and whether there are any suitable modern replacement component types for it as this type of component seems to be rather rare in supply and totally not used on newer parts (so something else must be used in its place?)

Can someone advise me on what to replace this with?

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Reply 1 of 13, by root42

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I am not an EE, but maybe you can simply get hold of another ferrit core and make your own inductor? You need new wire, make sure the insulation is not scratched, and then make 12 turns from the looks of it.

According to a coil inductance calculator (http://www.66pacific.com/calculators/coil-ind … calculator.aspx) My guess would be that this coil has roughly 1mH inductance. You can probably also get a commercial replacement, which looks slightly different. Not sure about other properties though, but the large gauge wire suggests that it has to withstand rather high currents.

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Reply 2 of 13, by Roman555

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I would try to find replacement on others damaged mainboards. A toroidal core of chokes are marked by colours. Colours depend on permeability.
So you just have to find a choke with the same size and colours, the same quantity of turns of winding and the same thickness of wire.

Last edited by Roman555 on 2018-12-21, 07:20. Edited 1 time in total.

Reply 3 of 13, by gdjacobs

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You can measure L for the choke:
https://daycounter.com/Articles/How-To-Measur … nductance.phtml

Ferrites are variable in mu, so calculating isn't going to be accurate.

All hail the Great Capacitor Brand Finder

Reply 4 of 13, by appiah4

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Sounds like too much hassle for a PCChips board I'm afraid 🙁

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Reply 5 of 13, by tayyare

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appiah4 wrote:

Sounds like too much hassle for a PCChips board I'm afraid 🙁

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Reply 6 of 13, by Roman555

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gdjacobs wrote:

You can measure L for the choke:
https://daycounter.com/Articles/How-To-Measur … nductance.phtml
Ferrites are variable in mu, so calculating isn't going to be accurate.

I think the material of the core of the choke isn't ferrite. They are called iron powder cores.

Reply 8 of 13, by gdjacobs

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I would expect an iron powder core to similarly have issues with variable mu. Best to measure the inductance directly.

Also, don't forget to measure DC resistance of the coil to factor in.

All hail the Great Capacitor Brand Finder

Reply 9 of 13, by appiah4

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gdjacobs wrote:

I would expect an iron powder core to similarly have issues with variable mu. Best to measure the inductance directly.

Also, don't forget to measure DC resistance of the coil to factor in.

All this is impossible for me to do if only for the fact I dont know how to do half of them.. 🤣

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Reply 10 of 13, by gdjacobs

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Measuring DC resistance can be done with the ohms setting of your multimeter. The other requires the use of an oscilloscope. You might be able to generate the test signal with a high def PC sound card, but I'd recommend using a signal generator in case you require higher frequencies. Let me know when you have access to those tools* and I can explain how to do the test step by step.

* check for any local maker spaces, ham clubs, or local universities and colleges if you don't want to purchase

There's a current analog of the capacitor voltage decay method which could also be used for measuring inductance.

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Reply 11 of 13, by nforce4max

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For a rough and quick repair just replace with another coil of similar size and possibly same or similar number of turns until you can find a proper coil. I've done double coil and double cap mods to improve overclocking as well just for fun on hardware that was recent up to 2010 or so and had no issue.

On a far away planet reading your posts in the year 10,191.

Reply 12 of 13, by appiah4

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Can I measure the dc resistance on the circuit or donI have to remove it?

The second will have to wait as I have no oscilloscope 🙁

Retronautics: A digital gallery of my retro computers, hardware and projects.