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RL02 debugging

Posted <2017-11-02 Thu 22:34> by Aaron S. Jackson.

Now that my PDP-11 is back up and running (woo!) I can finally start attempting to get my RL02 drives to work. Finding an official cable and terminator seemed impossible, so I decided to build my own. I showed this in the first post about getting my PDP-11.

I am basing my (messy) terminator on the schematic from here. From what I can tell, everything should be fine. Based on what I have read, it should just be a straight through ribbon cable with a terminator at the end. I've done the obvious tests, such as checking that the resistance between pin 1 and pin 2 is 82 ohm, and hence, the resistance between pin 2 and pin 4 is 164 ohm.

Taking a peek with the oscilloscope suggests that the controller clock signals (one seems to be the inverse of the other) are making their way to the drive.

The RL02 technical manuals says the fault light will be illuminated if any of the following occur.

Since I appear to have the clock, and have not reached a point where the drive is able to load, I am beginning to wonder if there is actually a fault with the drives (since both do this). The voltages from the power supply are fine. I was given a spare RL02 board when I got the PDP-11 originally, so I may try swapping one out and see what happens.

But that's for another evening.

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