PERQ T2 faults

[Tony Duell]

> 
> Tony Duell wrote:
> > What I would do is first check that the hard disk is going ready -- that 
> > is with a logic probe on the control connector with the drive cabled up 
> > to the PERQ.
> 
> Presumably I can do that on the bench - I think it's just a case of applying 

You can, yes. Althought personally, I'd do it in the PERQ (a 50 way cabel 
with an edge connector on one end and a 2-row header socket on the other 
is very useful for cabling the DIB to the EIO in this sort of situation 
;-)). Reason being that if the PERQ isn't asserting drive select or 
something, you'll spot that oo.

> power and twiddling the appropriate drive select line so that the drive 
> enables the output control signals... (I'll check via bitsavers - I think the 
> drive selects are active-low)

YEs, just about all the signals on the ST412 control connector (and for 
that matter a floppy drive connector) are active low. The drive outputs 
may well be (should be!) open-collector signals, requring an external 
pull-up resisotr.

A couple more things. The 3 wire power connector on the DIB is +5V, 
Ground, -5V. Not +12V anywhere.  And the DIB breaks the rules by using 
totem-pole drivers to drive the disk signals. if the power cable falls 
off, these darn things can assert the appropraite signals and corrupt the 
disk. Don't ask how I found that out!

> Worst-case if the drive's hosed, we've got various install disks - just a 
> question of whether there's a formatter (low or high level) in there somewhere!


The formatter wasn't included with any normal PERQ OS distribution. But 
you should have the engieer's disk somewhere that includes it.

-tony