Just finished repairing my poor Olivetti M24. I'm sooo relieved, i was almost resigned.
Some years ago i blew up a diagnostic card inside of it , maybe i did put it backwards(but i swear i triple checked it, and it was the right position), maybe paying 2 Euro shipping included for a dodgy card from China,without manual, wasn't the brightest idea....
The Poor old Olivetti was stuck even before the bios routines, no video , leds on keyboard frozen. I tried it without the isa 'riser' card, and i heard a beep from the speaker, indicating that the Pc has booted up.
So i did disassemble the Isa expansion board, desoldered all IC's and put sockets.
socketed board.jpg
I've recently bought an IC tester useful for the 74-- series of chips, abundant in all PCs.
fault 2.jpg
I did find one broken chip, a 74ls04. Replaced it and finally got a prompt back!
IMG_20200526_163114.jpg
It went better than expected... If the broken chip was , let's say, on the mainboard, i would have needed more patience and maybe a decent oscilloscope (and weeks to learn how to use it!)