RX02 Repair

From: steve.lubbers_at_barco.com <(steve.lubbers_at_barco.com)>
Date: Wed Aug 4 07:38:50 1999

Tony,

Thanks for the suggestions, I'll see what I can see tonight.

I have a copy of the RX02 Field Maintenance Print sets, so I can follow what
you are describing. I don't think I have a spare 2102, but could get one
easy enough.

I didn't think of the load/dump sector buffer approach. That sounds like I
good idea! Any programming help you have would be great! I was trying to
figure out how to get a logic analyzer, but your idea will use the drive to
diagnose itself.

I posted a follow-up on the mailing list. Essentially, as you said, the
disk does spin. I even checked the rotational speed. Plus/minus my
scope's accuracy, it is spinng OK.
I've cleaned the heads, but didn't go any further with mechanical
adjustments. I was assuming that a drive sitting in a box didn't fall out
of adjustment too far, and given that it reads a good portion of the data
correctly, I thought I would probably make things worse.



>>> -----Original Message-----
>>> From: ard_at_p850ug1.demon.co.uk [mailto:ard_at_p850ug1.demon.co.uk]
>>> Sent: Tuesday, August 03, 1999 1:43 PM
>>> To: Discussion re-collecting of classic computers
>>> Subject: Re: RX02 Repair
>>>
>>>
>>> >
>>> > I've been trying to bring my old RX02 drive back to life,
>>> with little
>>> > success.
>>> >
>>> > I just received a good bootable floppy, and get the same
>>> results as with all
>>> > my old disks, so now I'm looking for hardware problems.
>>> >
>>> > On a PDP-11/03, With RXV21 controller, and an RX02 drive,
>>> the RX02
>>> > initializes, attempts to read the boot block, and crashes
>>> to ODT at 000600.
>>>
>>> I am going to assume that this is a double-density disk
>>> (and thus has 256
>>> byte sectors) and that the DIP switch inside hasn't been
>>> moved since it
>>> last worked on an RXV21 (I can't find the info quickly, or
>>> I'd tell you
>>> how to set it).
>>>
>>> >
>>> >
>>> > > In examining what my system reads as it attempts to
>>> boot, it looks like I
>>> > > read every other 128 byte chunk correctly. I haven't
>>> figured out a
>>> > pattern
>>> > > to the corrupt sections.
>>> >
>>> >
>>> > Does anyone have any RX02 diagnostics, or hardware
>>> trouble shooting tips?
>>>
>>>
>>> Argh!. Fixing an RX02 is a lot worse than fixing an RX01 (I've done
>>> both). The RX01 has an internal diagnostic connector that
>>> you plug an
>>> KM11 into. You can then single-step the microcode,
>>> halt-on-error, etc.
>>>
>>> Anyway, back to the RX02. The controller is the upper board
>>> in the drive
>>> unit. Undo the screws and hinge it up. On it there's a microcoded
>>> processor based on 3 2909 sequencers and 2 2901 ALUs, 1K of
>>> ROM and a lot
>>> of TTL glue. There's also a 2K bit sector buffer based on 2
>>> off 2102 RAMs.
>>> I can talk you through it if you can get the printset.
>>>
>>> >From the fault, I suspect that most of it is working
>>> correctly (most of
>>> the logic is the same for all bits in the sector), and that
>>> the most
>>> likely problem area is the sector buffer and/or its address counter.
>>>
>>> There are some things you can try. Firstly (if you have the
>>> programming
>>> info - if not I'll find it), you can try transfering 256
>>> bytes from the
>>> PDP11 to the sector buffer and then transfering it back
>>> again (without
>>> going via the disk). This will test most of the controller
>>> logic and the
>>> sector buffer RAM. My guess is that this will fail.
>>>
>>> Now look at the siganls to E56 (a 2102 RAM that's the high
>>> half of the
>>> sector buffer). Does it ever get enabled (pin 13 goes low)?
>>> Check back to
>>> E29f (74LS04) if not. If that inverter is OK, then suspect
>>> the address
>>> counter (E63, E57, E51).
>>>
>>> Also suspect E56 itself (this is the most likely problem,
>>> actually). If
>>> you have a spare 2102-1, it may be worth replacing it.
>>>
>>>
>>> >
>>> >
>>> > Steve
>>> >
>>> >
>>> >
>>>
>>> -tony
>>>
Received on Wed Aug 04 1999 - 07:38:50 BST