Today I made some progress too. I was able to dump the O-FW of a 74850. So here is how it works (although I just tried it with one drive til now):
-Lift pin 101 and 122
-solder a cable to pin 100, pin 101 and one to 3,3V
-use a 2-way switch which either connects 101 to 3,3V or to 100
-put the switch into the position so that it connects 100 to 101
-start Dosflash, it will recognise the SPI with Status x72
-if you read it out now, it will just give you a .bin full of FFFFFFFF, but thats OK, this is how we tricked the Flash Controller to think the SPI is empty
-put the switch in the other position (so that 101 is connected to 3,3V)
-now read the flash
---> Voila, you got your dump!
Maybe someone else is going to give it a try, would be nice to get some feedback. For today my tests are finished, its pretty late....
Oh yes, and of course: no warranty at all, I even fried one drive myself a few days ago, when I was performing some tests. I suppose working on it a 4:30 in the morning obviously wasn´t the best idea...