hp 9121 (cctalk Vol 16, Issue 6)

[Tony Duell]

> But I suspect that the problem is a dirty R/W head on the drive.

My first question is : What sort of disks are you using? If you're using 
HD (PC 1.44 M byte) ones then you will have problems. The density-select 
hole will mean the disk-inserted sensor is not activated so the drive 
won't think it's got a disk in it. And even if you cover that hole up, 
the coercivity of the media is different between DD (which is what you 
shoudl eb using) and HD disks. The latter will _not_ be reliable!

> 
> You do not mention whether you have the 2 drive model (9121D) and
> whether you have the same error message when you try accessing the
> second drive. If you only have the prob with the first drive, then
> its almost certainly a dirty R/W head inside the drive.
> 
> Have you tried cleaning the heads? The easiest way is to try to
> find a cleaning diskette (usu available for PCs). Such diskettes
> usually have an extra hole across from the WRITE-PROTECT tab.

I am in two minds about this recomendation. On the one hand, if you've 
got no experience of dismantling electronic devices, it may be safer to 
use a cleaning disk. But those disks are very rough on the heads, I NEVER 
use one!

The 9121 comes apart quite easily. After disconnecting the cables at the 
back, it's a few screws on the back and the cover comes off (lift the 
back edge first I think). Each drive is hald down by 3 or 4 screws, and 
there are 2 cables to uplug. Then one screw on the back of the drive 
chassis itself holds the cover on. With that removed you can lift the 
presure pad carefully (this is a single-head drive) and clean the head 
with a cotton bud dipped in propan-2-ol.

But then I've worked on many, many such drives...

-tony