a very weird problem - need help getting it working

[Chyros]

OK, so get this.

I have an AT/XT switchable keyboard I wanted to review a while ago but I can't get it working properly. I've tried a whole bunch of things but the damn thing doesn't seem to work properly. Here's what I found.

-If I plug it into my PS/2 port with an adapter and start it up in AT mode, the computer gives a "no keyboard found" error.
-If I do the same in XT mode, it also gives a "no keyboard found" error (obviously).
-If I use an adapter plus a PS/2-to-USB converter (a Belkin) and start up the keyboard in AT mode, it doesn't work.
-If I do the same in XT mode, again, doesn't work.
-If I use an Orihalcon's converter and start it up in AT mode, it doesn't work.
-If I use an Orihalcon's converter and start it up in XT mode, it doesn't work.
-If I start up the computer with another keyboard plugged into the computer, wait for Windows to start, then hot-plug the board with Orihalcon's in AT mode, it doesn't work.
-If I start up the computer with another keyboard plugged into the computer, wait for Windows to start, then hot-plug the board with Orihalcon's in XT mode, it doesn't work.
If I start up the computer with another keyboard plugged into the computer, wait for Windows to start, then hot-plug the board with Orihalcon's in XT mode, THEN WAIT FOR A WHILE, then use it, it usually works. This doesn't work with AT mode.

What ye olde fukke is going on here?! Oo And more importantly, is there something I can do to fix it? Thanks!

[seebart]

If I start up the computer with another keyboard plugged into the computer, wait for Windows to start, then hot-plug the board with Orihalcon's in XT mode, THEN WAIT FOR A WHILE, then use it, it usually works. This doesn't work with AT mode.

Does it then work without strange behaviour normally?

[stratokaster]

I think the electronics are wonky. The first thing I'd do is change the electrolytic capacitors. While my experience in repairing digital electronics is very limited, I used to restore vintage audio gear. And I can safely say that dried-up electrolytes can lead to all kinds of weird problems.

[keycap]

It seems like a capacitor issue. I've personally never dealt with this before.

[Engicoder]

OK, so get this.
If I start up the computer with another keyboard plugged into the computer, wait for Windows to start, then hot-plug the board with Orihalcon's in XT mode, THEN WAIT FOR A WHILE, then use it, it usually works. This doesn't work with AT mode.

When you say "hot plug the board with Orihalcon's" do you already have Orhalicon's converter connected to the keyboard or is the converter plugged into the computer and then connect the keyboard to the computer.

I suspect this may be a power issue. PS/2 allowed keyboards to use up to 275ma of power while usb only supplies 100ma at enumeration. Many PS/2 keyboards pull more than 100ma, so the voltage may be dropping and the keyboard browning out. The computer may even be shutting down the USB port temporarily. If USB configuration descriptor in Soarer's code requests more power, it should be able to supply enough power once enumerated. I would try plugging in the converter and then attaching the keyboard.

[Muirium]

+1 to: check the capacitors. A delay like that isn't likely to be digital, it has analogue written all over it. Electrolytic caps reforming (or whatever the right word is) because they're bust. Swap 'em out.

[Chyros]

If I start up the computer with another keyboard plugged into the computer, wait for Windows to start, then hot-plug the board with Orihalcon's in XT mode, THEN WAIT FOR A WHILE, then use it, it usually works. This doesn't work with AT mode.

Does it then work without strange behaviour normally?

Yes, it works perfectly in this mode. Although of course it behaves like an XT board. It also has 2KRO in this mode, even though the keyboard is supposed to be NKRO.

When you say "hot plug the board with Orihalcon's" do you already have Orhalicon's converter connected to the keyboard or is the converter plugged into the computer and then connect the keyboard to the computer.

No, I don't have the converter in when I start the computer, I heard that can have weird side effects. I plug it in at the same time as the keyboard.

It could be the caps of course, but tbh they all look fine. I know they normally bulge and/or inflate when they go wrong, these don't look like that at all.

[stratokaster]

It could be the caps of course, but tbh they all look fine. I know they normally bulge and/or inflate when they go wrong, these don't look like that at all.

In my experience, this is mostly not the case. A capacitor may look as good as new, but its capacitance may be far below the specified value. Sometimes old capacitors that pass visual inspection are even open-circuit.

[Chyros]

It could be the caps of course, but tbh they all look fine. I know they normally bulge and/or inflate when they go wrong, these don't look like that at all.

In my experience, this is mostly not the case. A capacitor may look as good as new, but its capacitance may be far below the specified value. Sometimes old capacitors that pass visual inspection are even open-circuit.

Fair enough. Come to think of it, is there a way I can test them with a multimeter to see if they're okay?

[stratokaster]

It could be the caps of course, but tbh they all look fine. I know they normally bulge and/or inflate when they go wrong, these don't look like that at all.

In my experience, this is mostly not the case. A capacitor may look as good as new, but its capacitance may be far below the specified value. Sometimes old capacitors that pass visual inspection are even open-circuit.

Fair enough. Come to think of it, is there a way I can test them with a multimeter to see if they're okay?

I'm afraid you need an ESR tester to test capacitors in situ. If you remove the capacitor from the circuit you can use a multimeter with capacitance mode to measure its actual value (that's what I use).

iFixit has some useful tips regarding capacitors: https://www.ifixit.com/Wiki/Troubleshho ... components

[Muirium]

Usually, electrolytic capacitors will do you the service of politely urinating all over the PCB so you can tell they have expired. Look for the goo!

[Chyros]

Usually, electrolytic capacitors will do you the service of politely urinating all over the PCB so you can tell they have expired. Look for the goo!

Hmmm, what does this look like?

[Muirium]

Residue. Or worse…

https://en.wikipedia.org/wiki/Capacitor_plague

[stratokaster]

Residue. Or worse…

https://en.wikipedia.org/wiki/Capacitor_plague

It was a special case. Taiwanese manufacturers of electrolytic capacitors decided to steal Japanese trade secrets, but somebody got it wrong (I like to entertain the idea that the Japanese knew of ongoing industrial espionage efforts and leaked the incorrect formula intentionally). The resulting electrolyte produced lots of gases which led to capacitors becoming pressurised and bulging/splitting/leaking.

This usually doesn't happen to high-quality capacitors. In those the electrolyte just slowly evaporates over time leading to eventual failure. They rarely bulge or leak.

[Engicoder]

Electrolytics used to ooze goo when they failed. That's why manufacturers added the scoring to the tops so that they would vent instead and prevent damage to the pcb.

Overload failure results in a rupture and venting. Long term failure is usually due to the electrolytic drying up.

[Muirium]

Aye. Just go look at them, basically. Any funny business and they're due out!

The old caps I've had go wrong always had some (seemingly dry, perhaps long since evaporated) stain emerging from around them on the PCB. Macintosh SE/30s are notorious for this. Apple cheaped out and used crap on that $6,500 computer! And Steve wasn't even there for that one.

[Chyros]

Hmmm, no, there's nothing like that on the board.

Would you say it's most likely the can-shaped caps failed, or the little sideways UFO ones?

[Muirium]

The big cans are the ones I've seen go wrong. Purely anecdotal advice, but that's all I've got!

What's a sideyways UFO look like anyway?

[Chyros]

Fair enough, I'll see if the electrical workshop can spare a few.

The UFO ones are these ones:



I thought it was pretty descriptive anoi? 8)

[Engicoder]

Those are ceramic capacitors, referred to as "disc" capacitors. They are not as likely to fail due to age as electrolytics are.

[stratokaster]

I've never seen a ceramic capacitor fail (unless it's shattered)

[Engicoder]

Very true, they are considered the quite reliable, and very resistant to failure due to aging. The can "fail" If the outer coating is damaged as moisture and humidity can corrode the termination or be absorbed into the dielectric. Of course any capacitor can fail via overload, some, like tantalums, spectacularly.

[Chyros]

The keyboard hasn't seen much use tbh, it's very clean and the texture on the key caps is immaculate.

I'll ask the guys at the electronic workshop tomorrow if they can replace the cans for me, there's only two on it anyway. Hopefully that'll fix it. If it's a power issue, does anyone know how I would fix that? I have no idea how that would explain how it only runs in XT mode, let alone only after hot-plugging it, but still xD .

[Muirium]

Strange, time-dependent shit is the hallmark of leaking caps. They'll understand you just fine.