VOGONS


First post, by SETBLASTER

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Some years ago i managed to get a MODEL M keyboard, it looked like brand new, It has like a phone connector that later i learned it was an SDL connector. Of course the cable was not included for such a low price, but i still bought it.

Then looking online i found that people modded these keyboards because the "SDL 2 PS/2" cable might be expensive. (they bought a PS/2 extension cable, cut , and soldered into the motherl M motherboard.

https://geekhack.org/index.php?topic=55377.0

so i got a 60inch PS/2 extendion cable. I did the mod and it worked!.....well, sometimes it worked... it actually depends on the Computer motherboard you plug it in to. i have had mixed results, i have seen many things trying to use the keyboard.

For example :

Using a model M keyboard (PS/2 modded) and a "PS/2 to dimm" adapter:
- worked on many 486 motherboards. but some didn´t even detect the keyboard, not let me F1 or delete go to bios. (this is not fault of the adapter nor motherboard as i have other dimm keyboards and the motherboard works)

Using the Model M keyboard (ps/2 modded) and some pentium 3 motherboards, it worked perfectly. But on some motherboards it actually started to work fine but after 4 or 5 minutes hell went loose. typing letters gave numbers or symbols, and even the speaker started to sound crazy to the point the keyboard would not even respond anymore.

Tried to use the same keyboard with a PS/2 to USB adapter and the keyboard worked perfectly in DOS.

So my question is, are these old model M keyboard not compatible at all with more modern machines?
Is this a fault of the keyboard itself or from the motherboard manufacturer?
Is it possible that model M keyboard used a different voltage that PS/2 connectors cannot supply?

its very weird that the keyboard works sometimes depending on the motherboard. and PS/2 connector give a lot of issues.

Is there something that can be done to fix it?

Reply 1 of 9, by zerodiagonal

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s it possible that model M keyboard used a different voltage that PS/2 connectors cannot supply?

The one I use daily has some weird issues too and I suspected the same. In a normal boot, it'll freeze the computer (P4 3.0, 2GB, XPSP3) as soon as I press a key. I have to soft-reboot (CTRL-ALT-DEL) or even reset it immediately as soon as the NUM, CAPS and SCORLL indicators light, then all is fine.
I've tried to boot with the cable unplugged on the keyb end, as soon as I plug it back (live), it starts beeping and either freezes (if it's on the desktop screen) or beeps like hell for a couple of seconds and then behaves normally. If I boot with another keyb and then (live) switch to the Model M, something similar happens.
It seems as though it needs extra power to be initialized properly. I've tried to google this before but never came to any relevant results.

edit: the cable of mine is an original PS/2.

Reply 2 of 9, by BlackLinus24

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I have experienced something similar. The model M with original SDL- PS/2 cable would not be detected by my ASUS VL/I-486SV2GX4 motherboard. However, on my DFI Socket 7 K6/2 motherboard it worked perfectly. I did some superficial research and the best explanation I've found so far was that the Model M is quite power-hungry and the Asus motherboard might not be providing enough power for the IBM keyboard.

That said, I have a Model M keyboard from Unicomp, Inc. with PS/2 connector - and electronically it apparently should be the same as the original IBM Model M keyboard - and that keyboard is actually detected and works perfectly with my ASUS VL/I-486SV2GX4 motherboard.

Reply 3 of 9, by dionb

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Ran into this today. My standard retro setup is a model M hooked up to an Aten KVM switch. It always works with PS/2, but if I add a PS/2 to DIN (not "dimm") adapter, there are some boards it fails on. My guess is that the adapter adds attenuation to the signals and that the model M doesn't have a lot of headroom there, so that little bit extra pushes it over the edge on very sensitive boards. I've encountered this on an ECS (Elitegroup) SL486-E and a TK8498F.

Both work fine with a native DIN keyboard connected directly.

Reply 5 of 9, by SETBLASTER

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maybe it has to do something with how power hungry the keyboard is.
but i don´t know if it has to do something with the data or clk line

One thing we can do to test is to get a PS/2 extender cable, cut the voltage wire and have power from a usb port to feed the keyboard directly.
or could there be a KVM that feeds the PS/2 ports with an external power DC adaptor?

Reply 6 of 9, by SETBLASTER

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see here

http://swvincent.com/ibm-model-m-power/index.html

-----------Current in mA, LEDs on
IBM (Lexmark)------- 126
IBM (Lexmark) ------ 129
Unicomp ---------- 29
IBM 1395240 -------- 120

and according to wikipedia, the PS/2 Pin 4 VCC +5 V CC has 100 mA
but i don´t how how much mah can usb 1.0 provide

Reply 7 of 9, by Super_Relay

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A standard USB port should be able to provide 500mA according to the official specs for USB1.0 and 2.0 though dedicated charging ports can provide more

standard usb3 ports have upped that to i think 900mA.
usb3.1 bumps it even further.

Of course you can have manufacturers set higher limits, for example the usb2.0 port on a raspberry pi can provide 1200mA but 500 is a safe assumption for 1.0 and 2.0 before you trip over current protection on most devices

Reply 8 of 9, by Predator99

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I have some unmodified with a DIN connector. When plugged in a modern ASUS P8H67-M PRO (combo PS/2 mouse/keyboard connector) with a DIN-PS/2-adapter the IBM works well in the BIOS Setup. But when booting Windows, it doesnt work anymore.
Needed some time to find the solution: After starting Windows, you need to reboot once. With the 2nd boot, the IBM works also under Windows...strange thing but workaround works.