Problems with a DEC RL-01 drive on a PDP-8/A

[Tony Duell]

> >
> > http://www.technology.niagarac.on.ca/staff/mcsele/pdp8a.html) is
> > functioning properly but 'hangs' when the bootstrap is exectured for the
> > RL-01 drive (the FAULT light blinking briefly then extinguishing). The
> > RL-01 disks were last booted about 10 years ago and were supposedly
> > bootable then (presumably with OS/8).
> 
> You didn't say anything in your message or on your web page about
> the READY light. Is it lit when you mount the pack?  If it's lit, does it
> blink when you step through the bootstrap?

My first worry is that the fualt light blinks during the bootstrap. I 
don't think it should. 

> 
> It's a really fundamental thing, but since it seems that you recently
> acquired the system, did you lock the heads before transporting it?
> (small metal square with one screw on the corner that blocks the
> heads from sliding out during transport)  If someone else locked them,
> did you _unlock_ them?  If you moved the drive with the heads
> unlocked, that could be your problem.  If there was a pack in the
> drive at the time, that _really_ could be your problem.

My experience of RL01's and RL02's suggests that there is considerable 
friction in the positioner mechanism (unlike, say, an RK05), so it's not 
_essential_ to lock the positioner for transport. On the other hand, it 
does no harm to do so, and might save the heads.

> 
> Something else to check is the cable.  I have a PDP-8/a w/RL8A.
> I recall that the controller-end of the cable is somewhat fragile
> (for those that don't have one to look at, it's not like an RL11;
> it's a bare Berg connector with 40-ish wires coming out of a round
> RL cable in a twisted fan - more like the cables I've seen for an
> RLV12). I know on at least one occasion, I had to repair one of
> the outer conductors of my RL8A cable because the wire popped
> out of the crimp-on pin in the Berg connector.

I beleive all the cables are electrically identical. Certainly the RL8 
type of thing is used on an ELV11 in the MINC system. The main reason 
there are different cables is the physical problem of getting the cable 
round the inside of the system box -- with osme machines it's easier to 
use a ribbon cable, with others it's easier to use a cylindrical cable.

Anothre thought is that there's a PLL circuit in the controller used as 
part of the data separator (or at least there is in the RL11 and RLV11 
controllers). Maybe something in that has drifted over the years, and 
it's no longer locking. Or maybe some chip has just failed.

How I'd handle this (given my hardware background) is to remove the 
access cover on the drive, put a (scratch) pack in and spin up. Check the 
ready light comes on and the heads load.

Then write little programs on the PDP8 to read out the status registers 
etc. See if you can read the drive status, and see if it's reasonable. 
Try moving the heads to different cylinders (and actually watch the 
positioner to make sure it's doing the right things). Then try reading a 
sector. If you get an error, work out exactly what the error bits are 
telling you. TRen dive in with the 'scope and logic analyser to see what 
is settign those erorr bits, and work backwards until you find out why.

-tony