PDP11/23+ frustration

[Joe R.]

At 01:48 AM 6/18/05 +0100, you wrote:
>> 
>> Hi folks,
>> 
>> today I have powered up my Ampex DFR 996 removable/fixed combined disk 
>
>Argh! Powering up a devive (any device, but demountable hard disks are 
>one of the worst) is the last thing you should do. And in the case of 
>such a drive, I'd run the motors for at least 10 miuntes with the heads 
>prevented from loading (e.g. with the voice coil disconnected from the 
>servo amplifer) to 'purge' the air ducts, etc.

   When I was a FE I was real good at recovering data from damaged drives.
After repairing everything I'd vacuum out the drive chamber thoroughly,
then clean/replace filters, clean heads and platters, then run drive with
head load disableed (voice coil disconnected), then clean heads and
platters again and recheck the filters. Reconnect the voice coil and then
power up the drive with my finger on the UNLOAD button and IMMEDIATELY
unload the heads if they made any noise.


>
>> drive. After tweaking a bit around the address plug (btw does anybody 
>> have an original one?) I got it to start. It said to be ready only once. 
>> And made a horrible sound with the head of the removable disk. After 
>> that I tried it again but the drive just inserts the head for a short 
>> moment (with the same noise) and retracts immediately, shutting down.

   If the heads have crashed, they'll create enough drag on the disk that
it will go into an underspeed condition and that will cause  the heads to
retract. It will do this even on drives that don't have servo info on the
disk.


>
>Presumably you have a head crash. And the drive can't find the servo 
>information, so it retracts the heads. 
>
> 
>> Are there any opinions, spares, help, TOOLS for my situation? I have no 
>> clue if I could be able to find a new pair of heads and install them? 
>> Who has experience? What about the head alignment procedure?
>
>I've never seen this drive, but I have done head replacements on 
>demountable hard disks. It's not too difficult (not much worse than doing 
>a floppy drive). Of course you need the new heads.
>
>YEs, there's an alignment procedure. You generally have a special disk 
>pack that you put n, then connect a 'scope to the outputs of the read 
>preamplifier, and adjust the head position for even lobes of the catseye 
>pattern. Just like a floppy drive in fact. Again the problem is getting 
>the alignment pack.
>
>If you put good heads in, and they fly, you should be able to 
>format/read/write a scratch disk, even before you do the alignment. I'd 
>not put an alignment pack anywhere near a drive that didn't do that.

    Yes! Definitely test the drive with a scratch disk before risking those
expensive and hard to find alignment disk!!!

     Joe
>
>-tony
>
>