NOVA4 6070 disk booboo

[Jay West]

You wrote....
> Reassembled, READY, spinup, brush, head load.... CRASH. Top
> surface of the fixed disk unmistakably crashed.
>
> While I had the dust cover off the first time I did look at the
> heads and the platter surfaces. I didn't clean the heads
Almost always the problem is failure to completely clean the drive; heads, 
airfilter and ducts, all platters (both surfaces)... you've got to 
disassemble the platters, clean and buff them, clean the head armature, ALL 
internal cavities, etc. Yes, it could be a pre-existing crash. The above 
would have caught that ;) To clean an unknown HP 7906 drive for example, 
takes me a good 5+ days solid before even looking at mechanics, then 
electronics. You can't be too anal or thorough about this. One spec of dust 
is all it needs to poof. Working under an extremely bright light will 
educate on just how much dust is floating in the air :)

> Knowing that the platter was trashed, I took off the dust cover,
> cleaned the platter with a new pad, and felt for large bumps, and
> ran the READY sequence again. Crashed two more times then I
> stopped.
Yeah, I bet it did ;) Don't clean the platter in place, too hard to do a 
good job and buff it. Remove the platter. Also break out a dial test 
indicator and measure the runout/flatness (which you have to do when you 
replace it anyways).

> It suuuuure looks like the platters on the removable cartridge are
> physically the same as the fixed platter; and since I have two
> spare (three total) carts I may attempt surgery.
The key of course if is there is a designated servo platter, or if the drive 
uses a glass reticule with cylinder markings on it and an optical system. I 
can't speak for other drives, but at least on the 7905/7906 - the servo 
platter is actually a completely different magnetic coating from the data 
platters. You can see the difference when you get a good look at the 
platter. Servo head is different too. On the HP 7900A, the removable and 
fixed platters are identical (optical type drive).

I should buy stock in Kim-Wipes :>

Jay