AT Keyboard connector inductor bad? \ VOGONS

AT Keyboard connector inductor bad?

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First post, by Masejoer

Posted on 2022-03-09, 02:56

Masejoer Offline

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I have an Asus P5A -B here with a bad keyboard connector. I found that wiggling it would make the keyboard come and go - cleaned the contacts and re-soldered the connections to the board, but same thing. Further narrowed it down to this inductor - very light pressure on this component, the keyboard would come back. I went to re-solder its joints and re-tested - now I never get any keyboard detection.

Whether I have the jumper in either position, I get 5V on the left side, and 3.5V on the right with the keyboard attached, 80mV with the keyboard disconnected. I was getting 5V on both sides with the keyboard connector earlier, when it was in a loose state.

Any opinions on the correct course of action on resolving this? Any ideas of what inductor/specs that I could get to try in its place?

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Reply 1 of 6, by Horun

Posted on 2022-03-09, 03:27

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I would put the jumper in disabled (2-3) and temp short across L1 and see if the KB works. It should be somewhere from 1uH to 4uH and is for noise reduction if same as most later AT/early ATX boards. You might get away with out it....
fwiw: The manual at Asus does not show that jumper for P5A-B but does for P5A....just a observation

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 6, by Masejoer

Posted on 2022-03-09, 03:31

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Horun wrote on 2022-03-09, 03:27:

I would put the jumper in disabled (2-3) and temp short across L1 and see if the KB works. It should be somewhere from 1uH to 4uH and is for noise reduction if same as most later AT/early ATX boards. You might get away with out it....
fwiw: The manual at Asus does not show that jumper for P5A-B but does for P5A....just a observation

Yeah, I have it on 2-3 already, and a 1ohm resistor's leads touched to the pads brings the keyboard to life.

Last edited by Masejoer on 2022-03-09, 03:33. Edited 1 time in total.

Reply 3 of 6, by jmarsh

Posted on 2022-03-09, 03:33

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Would suggest making sure the resistance of the fuse is close to zero.

Reply 4 of 6, by Masejoer

Posted on 2022-03-09, 03:35

Masejoer Offline

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jmarsh wrote on 2022-03-09, 03:33:

Would suggest making sure the resistance of the fuse is close to zero.

Yes, 0.1ohms after zero'd to the probe wire's normal resistance. Jumpering over the fuse with multimeter probes shows no change in behavior. Do the same on the inductor, keyboard lights up.

Reply 5 of 6, by Horun

Posted on 2022-03-09, 04:04

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Sounds great so maybe you could check that resistor to see if it uses wire and has some inductance (basically some low R value resistors use wire wrap internally and not carbon) which you could then use as L1 instead of trying to order a SMT inductor.
Just a thought 😀

added: check Mouser, they have many SMT inductors if you want to replace it near exact....

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 6 of 6, by Masejoer

Posted on 2022-03-09, 06:07

Masejoer Offline

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Horun wrote on 2022-03-09, 04:04:

Sounds great so maybe you could check that resistor to see if it uses wire and has some inductance (basically some low R value resistors use wire wrap internally and not carbon) which you could then use as L1 instead of trying to order a SMT inductor.
Just a thought 😀

added: check Mouser, they have many SMT inductors if you want to replace it near exact....

Yeah, I can grab some inductors if I knew which to look for. Also not sure it matters much - a 4uH seems fine if that's the range I'd be going for. I have no idea what motherboards typically use here.

I'm not concerned with reworking SMD components, and this thing isn't small enough to need my microscope. I just don't have any tiny inductors in my inventory as I've never needed them!

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