Core memory repairs, part 2.

I spend some more time on the severely defective 8/L core stack I have. First I repeated the diode checks and wielded out all diodes that were more than 40mV away from the .55 V forward voltage that seems to be standard. Total number of defective diodes : 29 . Still cannot figure out why so many diodes were dead/shorted. Also repeated the inhibit / sense wire checks : 1 sense wire open. 1 sense wire high ohmic. ( 200 ohms ) 1 inhibit wire high ohmic ( 250 ohms ) Normal value for sense / inhibit wires would be around 15 ohms. I then opened the stack by cutting through 128 X/Y wires and removing 256 wire halves... There were several old repairs, covered with some ceramic substance, luckily all on the edges of the core mats. The high ohmic wires were due to this old repairs, after scrubbing off the ceramic stuff and resoldering the connection the high ohmic sense wire was restored to its nominal 15 ohm value. I still have to fix the other wires, ( i.e. 512 wire halves to remove...) and reassemble the stack, but it looks like core memory repairs are possible by amateurs. Material needed : - high powered, but comfortable, microscope. - SMD pencil soldering iron. The smallest I could find, and it was still too big. - the smallest solder I could find, still way too big. The other core stack, with the one single bit error, is still closed, but by swapping sense wire I was able to confirm that the error is indeed in the stack. Jos Dreesen