Home brew receiver problems, works on several computers but not on all

[Hendrik v. d. B. <ch...@is...>]

I don't get it. I've built my own home-brew serial port IR receiver and so 
far it works on various configurations but not on all... I've made the 
device exacly as specified on the http://www.manoweb.com/alesan/lirc/ 
website (including Conrad Part Numbers). So far I get these results:

My Celeron 300 laptop - Windows 98 - Works perfectly fine
My Athlon 1200 desktop - Windows - mode2 just NEVER gives any signal when 
pressing buttons
My Athlon 1200 desktop - Linux - mode2 just NEVER gives any signal when 
pressing buttons
My Duron 1200 desktop - Linux - Works perfectly fine
My Duron 1300 desktop - Liunx -  mode2 just NEVER gives any signal when 
pressing buttons

The stranger thing here is, that if i gently remove or reinsert the device 
into the COM port, the computers which do not give any signals through will 
suddenly display values! At the moment the receivers hits the pins on the 
COM port, a signal seems to appear. So it seems that the device a least 
does something.

The problem is, that i just NEED to connect the receiver on my own desktop 
Athlon 1200 and there it just does not work at all... I also use a serial 
cable between my Siemens C35i mobile phone and the computer and that device 
just works perfectly fine on the COM port of this Athlon 1200...

What could be the case here? Voltage problems? But why does it work on a 
laptop then? I hope someone can clear this out for me....

Regards, Hendrik