PDP11/23+ frustration

[Tony Duell]

> 
> 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.

> 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.

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.

-tony