Old Label Dell AT 101 USB problem

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hellothere

25 Nov 2021, 22:07

Easy summary: no USB adapters seem to work. Works great over PS/2 (original cable). The best it does with a USB adapter is act like a random key is held down and/or the lock lights might flash.

I had initially thought it was some interesting ground issue because I had to remove the mylar/metallic-looking sheet that was attached to the mounting plate to get to the PCB. (I had to sand down the mounting plate, because rust.) I got a new roll of copper tape and made sure that I had unpainted surfaces for the tape to connect to. Didn't make a difference.

I'm probably going to make a Soarer's and a Hasu just to test, but the connector on the PCB for the cable is 7 pins.

Any other ideas?

User avatar
Palatino

25 Nov 2021, 23:03

Does it behave like this even when you plug it in and then turn the computer on? One of my old AT101s can be pretty picky about when it’s plugged in and unplugged, and if it’s not happy it will spam a key too, usually the Scroll Lock or whatever key it is that does Lower Brightness on a mac, plunging my screen into darkness.

User avatar
hellothere

27 Nov 2021, 21:29

Double-checked. Yes, it behaves like this even when the computer's off and I connect the cable, etc.

User avatar
hellothere

29 Nov 2021, 03:22

I broke out my trusted multimeter. The 7 pins from left to right on the PCB are:

Yellow / Clock
Black / Data
Red / No clue
White / Ground
Green / VCC
Black / Shield (PS/2 cable)
Black / Shield (PS/2 cable)

I connected a Soarer's to the matching 4 pins on the PCB (data, clock, ground, VCC). Keyboard works fine. Lock lights work. NANI?!

I don't want to tear apart the cable, but I'm interested in determining what that red wire does and why it has two cables for the shield. While I've proven that I can easily connect a Soarer's, I wonder what functionality I'm losing by not using 3 of 7 wires.

I think I'll build a Soarer's with a PS/2 female end to see what would happen if I connect the Dell's keyboard cable to it.

User avatar
Polecat

29 Nov 2021, 03:49

Where is the red connected on the PS/2 end? That will tell you what it does. Does the keyboard have an XT mode? If so the red may be a reset pin. The shields are there to keep the keyboard signals from interfering with your TV, or your neighbor's pacemaker. That's what those FCC numbers are all about. Normally a shield is connected to ground at one end (but not both).

User avatar
hellothere

29 Nov 2021, 16:44

> Where is the red connected on the PS/2 end?
That's the fun thing. It doesn't go to any of the pins or shield on the PS/2 male end. It also doesn't go to the keyboard frame.

> Does the keyboard have an XT mode?
As far as I can tell, nope. There may be a jumper someplace, but no switches.

> The shields are there to keep the keyboard signals from interfering with your TV, or your neighbor's pacemaker. That's what those FCC numbers are all about. Normally a shield is connected to ground at one end (but not both).
Yup. I've also seen a couple of old-label Dells without the shield, too. Well, it's easy to rip it off the case ...

User avatar
hellothere

29 Nov 2021, 22:09

I built a Soarer's that I attached to the female end of a PS/2 cable and attached it to the male PS/2 end of the keyboard cable. Works fine.

Well, I guess I can't complain. It's working either way!

User avatar
Polecat

30 Nov 2021, 04:21

hellothere wrote:
29 Nov 2021, 16:44
Yup. I've also seen a couple of old-label Dells without the shield, too. Well, it's easy to rip it off the case ...
I meant the shield in the cable, but same idea. F'in Cousin Charlie was mostly concerned that you might miss the commercials during Magnum PI, not that your keyboard would work properly during a nuclear blast.

User avatar
hellothere

30 Nov 2021, 20:19

I remember Magnum PI ...

User avatar
Palatino

30 Nov 2021, 23:49

It may return very soon, in the form of the next big Covid variant! Glad you got the Dell up and running again. Salmons + PBT make a lovely sound.

User avatar
hellothere

02 Dec 2021, 21:04

The only unfortunate thing is that I do retr0bright all keycaps. The Dell PBT ones are a creamy color that resembles what's on a newer Dell. So, you've got this shockingly white spacebar under all those cream keys ...

I'm giving strong consideration to just making Soarer's converters for any higher-end keyboard I sell, rather than using a 5-Pin DIN to PS/2 adapter + a PS/2 to USB adapter. I can make one for under $20, internal or external, and I can make them look nice. Not as nice as Orihalcon's, but better than just "acceptable." I can make a TMK for about $10 more and that's only because a Teensy is $10 more than a decent ProMicro clone.

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