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

Mark Csele mcsele at
Thu Sep 7 20:36:49 CDT 2006

I did some basic diagnostics on the system.  First, checked the
superficial stuff like the cable.  The Berg has a strain relief attached
and all wiring looks solid at that end.  Also checked the head lock
which was indeed in the lower (free) position however I observed the
head suring loading and it does indeed retract properly ... when the
LOAD key is out the heads retract immediately to the parked (fully
retracted) position.  When a fault occurs, heads pull back as well. 
True, the unit was transported without the head lock in place - any
ideas on possible misalignments?

When the BOOT switch on the limited-function panel (or the BOOT key on
the console) is pressed, the FAULT light blinks momentarily, the READY
light goes out momentarily, and the disk is restored to the original,
ready, state.  When the cartridge is loaded, the heads move from the
parked state to engage the disk.  During the fault the heads pull back
to the parked state and are then restored to the disk again.

When the bootstrap is stepped, the READY light never does blink (stays
lt), nor does the FAULT light!  Which leads me to wonder why?  Checked
the ROMs on the 8317 board - they are labelled '469A2' which I can't
seem to track.  Bootstrap option switches are set as SW1: 2,4,8 ON, SW2:
1,6 ON so with the older ROMs one would expect a TA8-E device (obviously
different or these ROMs).  Can I verify the bootstrap code easily?

Now, when I do step-through the bootstrap I have loaded (at address 1 -
the one on my web page), the address is seen to step through as follows:
1,2,3,27,30 (with AC=0004), 31,33,34,27,4,5,27,30,31,33,35,1 at whch
point it repeats in an endless loop.  It seems to fail, then, on the
read header function (at which point I did the diagnostics I had
outlined finding the DCRC error after which I did a get status.

I'd be grateful for any further ideas you might have on the subject
otherwise it might well be 'get out the scope' time!

Thanks .... Mark

Professor Mark Csele
Niagara College, Canada
300 Woodlawn Rd., L-8
Welland, ON, L3C 7L3

(905) 735-2211 x.7629
E-Mail: mcsele at
Author of "Fundamentals of Light Sources and Lasers", Wiley, 2004

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