I had to wait until the afternoon to receive my level shifter components to complete the rewiring of the interface board to the disk drive. I did clean up the board, removing the old IC sockets that will be replaced by the level shifter MOS transistors. Now I just wait for delivery.
I did some static testing of the wiring for the first 8 output signals that I converted to the new level shifter components. I decided to hook up to the disk drive and observe the signals with the scope to be sure I am getting what I expect before I continue on wiring more components.
First trial didn't show any change in the output from the fpga, therefore not surprising that the 5V level on the disk cable didn't change either. I added LEDs to confirm that the seek FSM was firing and emitting the proper cylinder signals, then tested again.
I am seeing the signal drop nicely, but something is not working as I expected. With the fpga board removed from the extender card, thus the fpga output disconnected, I can use a wire to pull down the input of a level shifter and see the resulting signal out to the disk drive drop to almost zero.
However, I am seeing my power supply drop out, even though it is feeding nor more than 70ma to the level shifter board. I think this may be a consequence of power coming from the terminator circuit onto the board. I need to do research to sort out what is happening and correct it before I finish up the board and begin disk testing.