Serial Interface Problem

[C.Schlehaus]

Hi,
today I tried to connect an FLUKE Scopemeter by serial link to my A31p. Unfortunately, the connection did not quite complete, as the software stopped by "Formatfailure", which is according to the help file by connection lost.
I had similar problem in the past, while a simple 3 wire interface is okay. Maybe the infrared serial link (to prevent any ground loop) for the FLUKE is operated by powering it from the serial interface itself (RTS and ?) and these pins are not okay?
Any hint how to test all interface pins to be okay?
Which IC is installed on the mainboard (to replace it in case of faulty device)?
Thanks a lot, Carlhermann