11/45 RL02 faults when RX02 is on

[Tony Duell]

> 
> Ok, is there a known severe RFI problem with mounting a RX02 directly on top 
> of a RL02 in an H960???

I've not heard of one, but then again, I've never actually tried that 
mounting arrangement. I know DEC stated that certain peripherals should 
have their own racks, I always figured this was, in part, to sell more 
cabinets, but I assume there might have been some interference issues as well


> 
> I went back to look at the "RL02 faults when RX02 is on" problem. I had left 
> the rear top cover of the RL02 up in the service position (with the drive 
> extended from the rack). I retested without touching anything. Sure enough, 
> the problem was "gone". The RL02 wouldn't fault no matter what. So I put 
> that rear top cover back down and screwed in the 4 screws, then pushed the 
> RL02 back into the rack and voila - the problem reoccured. The RL02 will 
> fault just after spinup IF the RX02 (which is mounted directly above it) is 
> powered on. Aha... I was now thinking a cable problem! I figured pushing the 
> RL02 in and out of the rack seemed to be the causative factor, bending a 
> cable just right or something.

The spindle motor in each drive of the RC02 is a fairly crude induction 
motor. I could well believe it has enough stray field to cause 
interferende (It's not that well shielded). Maybe that's being picked up 
by the RL's head and upsetting the servo.

Here's an idea. Take the fan plenum off the back of the RC02 (4 screws, 
IIRC, and uplug the fan calbe). Then unplug the 3 pin connector on the 
back of each drive (115V AC to the spindle motor). Try the system now. 
Obviously the RC02 can't run (the spindles won't be turning), but if 
there are no disks in the drives the system can't realise this. Have the 
RC02 powered up (so its PSU is running, and all the logic is powered) and 
see if the RL behaves now. If so, it pretty much confirms it's 
interference from the RC02's spindle motors.

-tony