VOGONS


First post, by Nailz

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I was wanting to use this for a new project, love that it has an ISA slot, hoping to make it into a high end DOS box (I realize it's overkill, but it's what I have at the moment, hoping it's not too much)... I appear to have a broken component and unsure what the ramifications would be to trying to use this motherboard. So here they are, starting with the dumbest first...

1. What is this broken component?
2. Does this need to be replaced?
3. If so, where would I find the part and what specs am I looking for? Is this something anyone can do or is it a difficult task?

Appreciate the help!

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Reply 1 of 16, by kalohimal

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It's a ferrite coil used in the output section of the DC-DC converter, for filtering the output ripples. Judging from its location it's probably for the RAM voltage. You could plug one from another broken board and it will probably work, even though the inductance won't be exactly the same.

Reply 3 of 16, by kalohimal

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The DC-DC converter is like a switching power supply, it takes in a DC voltage and switch the transistors (MOSFETs) on & off to generate the output (the method is called PWM). The duration of on time vs off time (duty cycle) determines the output voltage, so if PWM is 50% the output is roughly equal half the input. Because of this switching on & off, the output voltage becomes "choppy" and needs to put through an output filtering circuit (the electrolytic capacitors and the coil) to smooth it out.

Without any schematic, the only way to tell the inductance is to measure it with an inductance meter when it is good. But usually the circuit is quite standard and straight out from the datasheet. If you could read the part number of the PWM ic (or take a close up picture of it showing the part number), then we could check its datasheet to see if we could find the value. The PWM ic is the one at the lower right corner.

Reply 4 of 16, by kalohimal

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Here is my KT7 (non A) circuit. It is using an HIP6004 pwm controller ic. The value for the ferrite coil is 3uH. In yours I could roughly see that it is an ST chip. But they are about the same so I would say 3uH is good.

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Reply 5 of 16, by cmc

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A side note... I had two KT7A motherboards just like this one. Both eventually died of the capacitor plague. Symptom was that it developed a random reboot or two, then just failed to POST at all. I tossed them a few years ago, but it would have been smarter for me to install new capacitors. Just FYI in case you have issues with the board later.

Reply 6 of 16, by Nailz

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Thanks for the replies! So I am looking for a 3uh coil inductor? I don't seem to be able to find anything that looks like this thing. Everything I see that actually looks like what I have shows to be 200 to 300uh.... is there a better place for me to search?

Reply 8 of 16, by Nailz

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Ok, apologies yet again, you mentioned the PWM ic being in the lower right hand corner.... There are 4 corners, which one would identify as lower right... I will happily take a picture, is it next to the bad coil?

Reply 13 of 16, by kalohimal

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Yeah according to ST's Application Note for the L6911B, the coil is 3uH (page 7, "Inductor"). The spec is "3uH, T5052B core, 10T-16AWG" (page 13, L2), meaning the ferrite core part number is T5052B, and use 16AWG inductor wire to wind 10 turns. I've done a brief search on eBay and couldn't find it. Perhaps you could get one from another broken motherboard which has similar coil (about the same size, about same wire thickness, same 10 turns winding).

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Reply 14 of 16, by kalohimal

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Ok, aliexpress seems to have them. You can slowly browse thru and look for 3uH , 4A or greater ones. Otherwise you can also get those green ferrite core with the exact same dimensions, unwind the existing one, and wind back the inductor wire onto the new core.