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Old 12-20-2018, 04:05 AM   #1
appiah4
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Default Replacing a choke coil

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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Old 12-20-2018, 07:28 AM   #2
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Default Re: Replacing a choke coil

if you get the datasheet for the driver chip, it may have an example schematic with the values of the inductors.
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Old 12-20-2018, 07:32 AM   #3
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Default Re: Replacing a choke coil

Quote:
Originally Posted by stj View Post
if you get the datasheet for the driver chip, it may have an example schematic with the values of the inductors.
The chip in question is a TL494CN; I believe this is the correct datasheet to check? http://www.ti.com/lit/ds/symlink/tl494.pdf

I'm not exactly electronics literate so if you could point out where I should look, it would be extremely useful..

Last edited by appiah4; 12-20-2018 at 07:36 AM..
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Old 12-20-2018, 09:50 AM   #4
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Default Re: Replacing a choke coil

Quote:
Originally Posted by appiah4 View Post
The chip in question is a TL494CN; I believe this is the correct datasheet to check? http://www.ti.com/lit/ds/symlink/tl494.pdf

I'm not exactly electronics literate so if you could point out where I should look, it would be extremely useful..
The 494 is a generic PWM controller chip. It can be used for all sorts of different applications with completely different topologies. The datasheet isn't going to tell you anything useful about the implementation on your board.

What model of motherboard is it?

I probably have one here I can take a look at and figure it out for you, though the actual value isn't likely to be super critical as long as it is high enough to filter appropriately.
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Old 12-20-2018, 10:24 AM   #5
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Default Re: Replacing a choke coil

It is a PCChşps/Elpina M534 VXPro+

Can you tell me the cap ratings of EC12 and EC17 as well if possible?
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Old 12-20-2018, 10:35 AM   #6
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Default Re: Replacing a choke coil

The Inductor looks to be used for Buck converter (see how the Inductor and the diode are connected to verify), not for filtering so you need to get the correct one otherwise the output Voltage will not be correct.
Look at the application circuit of that 494 spec sheet.
Page 17 has the inductance calculator but you need to know many requirement info to come up with the correct inductor.
BTW, what is the color of that TOROID Ferrite/or Iron powder core? Light Blue? Gray?
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Old 12-20-2018, 01:31 PM   #7
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Default Re: Replacing a choke coil

I think that toroid is a Micrometals powdered iron core, this part number.
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Old 12-20-2018, 10:57 PM   #8
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Default Re: Replacing a choke coil

Quote:
Originally Posted by budm View Post
The Inductor looks to be used for Buck converter (see how the Inductor and the diode are connected to verify), not for filtering so you need to get the correct one otherwise the output Voltage will not be correct.
Look at the application circuit of that 494 spec sheet.
Page 17 has the inductance calculator but you need to know many requirement info to come up with the correct inductor.
BTW, what is the color of that TOROID Ferrite/or Iron powder core? Light Blue? Gray?
I looked at the inductor application and saw there was no definite value as well.. The tiroid is light blue on one side and on the interior suface, pale green on the other side and the exterior surface if that makes sense.

Quote:
Originally Posted by PeteS in CA View Post
I think that toroid is a Micrometals powdered iron core, this part number.
I guess *assuming* that I can source this I can reuse the wire to wrap 12 coils around it and it should work?

The closest affordable part I have found is this: http://tr.aliexpress.com/item/TR10-8...777238179.html but it has 14 coils instead of 12.. I guess I could unwind two of the coils and use it as such? Sorry if these are stupid questions, I am really in way over my head here..

This is probably going to be too much work for a generic PCChips motherboard..

Last edited by appiah4; 12-20-2018 at 11:06 PM..
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Old 12-21-2018, 11:47 AM   #9
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Default Re: Replacing a choke coil

You could reuse the wire, if the varnish isn't scraped and the wire shorting to anything.
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Old 12-22-2018, 06:25 AM   #10
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Default Re: Replacing a choke coil

What are the chances of frying a cpu if I blindly replace with the choke from aliexpress I linked above? The relevant controller chip is on the CPU VRM after all.. But the part seems fairly identical, just 14 coils instead of 12 so likely 10-15% higher inductance?
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Old 12-24-2018, 08:24 AM   #11
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Default Re: Replacing a choke coil

That rather depends upon whether as previously mentioned this is being used as part of a buck converter, draw out the circuit around the inductor and discrete components around it. And or put up some high resolution pictures from both sides of the board in that area.
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Old 12-25-2018, 10:49 PM   #12
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Default Re: Replacing a choke coil

Quote:
Originally Posted by llonen View Post
That rather depends upon whether as previously mentioned this is being used as part of a buck converter, draw out the circuit around the inductor and discrete components around it. And or put up some high resolution pictures from both sides of the board in that area.
Happy to oblige with pictures..
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Old 12-31-2018, 11:52 PM   #13
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Default Re: Replacing a choke coil

Quote:
Originally Posted by llonen View Post
That rather depends upon whether as previously mentioned this is being used as part of a buck converter, draw out the circuit around the inductor and discrete components around it. And or put up some high resolution pictures from both sides of the board in that area.
This IS a buck converter and it is for the CPU.

A lot of old motherboards used a 494 PWM controller for the CPU VRM / buck converter - mostly lower-tier boards like ECS and PCchips. They did that even as late as the Pentium 4 (Northwood) era. In any case, if you see a TL494/DBL494 on a PC motherboard, it is VERY LIKELY for the CPU VRM (and very likely, you have an ECS motherboard, as they -loved- using those TL494 designs for some reason.)

Quote:
Originally Posted by appiah4 View Post
What are the chances of frying a cpu if I blindly replace with the choke from aliexpress I linked above? The relevant controller chip is on the CPU VRM after all.. But the part seems fairly identical, just 14 coils instead of 12 so likely 10-15% higher inductance?
Well, don't blindly replace it.
Make sure the replacement inductor has at least the same core size as yours and the wire thickness is the same. If those match and the core type matches (powder iron or ferrite), then the extra 2 turns (and thus slightly higher inductance) shouldn't be that much of an issue.

That said, instead of unwinding this replacement inductor and winding it back with the old wire, you could instead just unwind 2 out of the 14 turns to make it 12 turns again.... Though again, the slightly higher inductance shouldn't hurt that much. After all, this is a TL494 buck regulator running at a fairly low switching frequency (probably 20-40 KHz, if even that much).

Last edited by momaka; 12-31-2018 at 11:54 PM..
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Old 01-01-2019, 10:58 PM   #14
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Default Re: Replacing a choke coil

Quote:
Originally Posted by momaka View Post
Well, don't blindly replace it.
Make sure the replacement inductor has at least the same core size as yours and the wire thickness is the same. If those match and the core type matches (powder iron or ferrite), then the extra 2 turns (and thus slightly higher inductance) shouldn't be that much of an issue.

That said, instead of unwinding this replacement inductor and winding it back with the old wire, you could instead just unwind 2 out of the 14 turns to make it 12 turns again.... Though again, the slightly higher inductance shouldn't hurt that much. After all, this is a TL494 buck regulator running at a fairly low switching frequency (probably 20-40 KHz, if even that much).
Well, the old one seems to be around 7.5mm internal and 12.5mm external diameter and roughly 5mm width, with an iron powder core. The one on aliexpress is a T50-52, so checking up on that standard it should be 7.7mm, 12.7mm and 4.8mm respectively, pretty much a good equivalent I would think.. I will just buy it and solder it on. What can go wrong I doubt I would damage a test CPU (and I do have more than enough 166MMXs to go around).. Fingers crossed, order placed, I will let you know in a month's time.
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Old 01-09-2019, 03:25 PM   #15
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Default Re: Replacing a choke coil

I think it will be fine too. 8.3 uH sounds about right anyways. Modern motherboards with their high frequency switching VRMs typically use 1 uH inductors or lower (that is, 1R0 or lower, like R47, R22, etc.) And in the mid-2000, I think most CPU VRM circuits used slightly bigger inductor values typically around 1 to 4.7 uH. So again, I think 8.3 uH is about right for this board with its slow switching TL494.

Besides, if you have too high of an inductance, the worst that can happen is low voltage to the CPU. But if the inductance is too low (way lower than the circuit expects), you can damage the CPU. So in your case, I think you're safe, as 8.3 uH is a fairly high inductance for a buck regulator.

Anyways, keep us posted how it goes.

Last edited by momaka; 01-09-2019 at 03:27 PM..
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