XP-50 MIDI OUT damaged. A question for the electronic savvy. (with diagram)

[Alexander333]

My beloved XP-50 has a fault in the MIDI OUT . The rest of the workstation works ok. The MIDI IN works fine.
I had a storm with lightning that hit my house. ALL MY STUDIO was unplugged and completely isolated from the electrical, telephone, network, etc supply. I suppose there was some kind of electromagnetic pulse that resulted in two devices with fried MIDI OUTS and a USB port in the computer. The midi interface was not damaged (Roland UM-2G)
I downloaded the diagram of the expansion board that I suppose has the problem (hope so) and I have a question If anyone can help me.
I'm able to solder but I do not know how to investigate the failure.
I do not see any component burned or damaged.
It looks that the HD74LS08P is kind of an amplifier for the UART data coming from the motherboard. Maybe is one of the transistors?

Does anybody have any suspect component that I can try to replace?

Thanks a lot!

 

[happyrat1]

Check Q9 PNP Transistor for opens and shorts. You may have to remove from circuit to test.

Also do a check output at pin 3 of IC4 with a logic probe or a scope to see if there is any output.

Those are the two most likely culprits.

Gary

 

[Alexander333]

Thank you very much Gary.
I will try and will post the result here. Thanks again.
Alex