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PS/2 Port Stopped Working

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First post, by CesarDRK

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Recently i was playing Monkey Island II in my msdos machine, using an AT keyboard + PS/2 optical mouse in pure MS-DOS, and suddently my dog tripped on the mouse cord, and it fell of the table.
The game kept playing with sound, but the controls were halted. So, i turned it off the machine then back on. After that, the mouse stopped working for good.

I have made some basic troubleshooting, but with no success:
- Checked if there was a connection break between the external PS/2 port pins to the motherboard 5-pin JST connetor - no issues, it was OK.
- Checked the voltage from the PS/2 port when the motherboard was ON (without the mouse connected) - seens fine giving +5v, so i think it´s OK.
- Tried to connect the mouse to another computer, and it worked fine!
- Tried connecting a PS/2 keyboard to the PS/2 port, same simptons of the mouse.

The simptons are:
Mouse turns on, flashes optical sensor for a few seconds, and then turns off (in the memory check screen of the bios). It is not detected under dos or windows.
PS/2 keyboard same situation, flashes two times (status lights) then stops. Bios says keyboard not found. To be honest, i have never tested a keyboard in this port before (i use an AT keyboard), i´m not sure if it worked before!

Specs are:

What could be the issue?

Thanks

Reply 1 of 6, by Warlord

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The keyboard or mouse should not draw more than 275 mA from the host
I don't know if you can damage the motherboard by unplugging, but there's been a myth that hot plugging could. \
If thats the case there should be a resistor that is burned out, and you would have to replace that.
The other possible scenario is the dog bent one of the pins on the bracket or external port. Or if its not a bracket but a port cracked a solder joint there or bent a pin.
It should be fixable.

Reply 2 of 6, by CesarDRK

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Warlord wrote on 2021-02-27, 01:50:
The keyboard or mouse should not draw more than 275 mA from the host I don't know if you can damage the motherboard by unpluggi […]
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The keyboard or mouse should not draw more than 275 mA from the host
I don't know if you can damage the motherboard by unplugging, but there's been a myth that hot plugging could. \
If thats the case there should be a resistor that is burned out, and you would have to replace that.
The other possible scenario is the dog bent one of the pins on the bracket or external port. Or if its not a bracket but a port cracked a solder joint there or bent a pin.
It should be fixable.

It didn´t got unplugged when the dog tripped. It just stretched/bent the cable with force, and the mouse went down the table to the ground and stopped working on the computer.

Btw, my electronic knowledge is very limited. I have only a digital multimeter, so i measured the voltage again, but with both the mouse connected and disconnected.
The m/b pins still gave me a stable 5.05v from boot to when the mouse led turns off.

The pins on the bracket/external port seen fine, but i´ve ordered another PS/2 bracket with JST connection to try, will see during the week when it arrives.

Reply 4 of 6, by dionb

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Let's see...

The mouse in known-good on other system, so it's definitely port-side. Also, the mouse initializes itself with power- on, which suggests that +5V and GND are fine. That leaves two suspecst: CLK and DATA.

First thing to do is to check continuity between the port/bracked and the header on both those lines. If continuity is bad on one or both, the problem is in your port/header cable and the new bracket you've ordered should solve your problem. If continuity isn't the issue, your dog may have damaged something on the motherboard. Follow the traces and see where they lead. There might well be a fuse on one of the lines.

Reply 5 of 6, by CesarDRK

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The bracket arrived, and oh well, it didn´t solve the issue.
I´ve also ordered a passive PS/2 -> SERIAL adapter and my mouse doesn´t work (i guess it doesn´t support the serial protocol).

I guess something must be faulty at the motherboard side then.

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