Shugart 851 power problem

From: Dwight Elvey <elvey_at_hal.com>
Date: Tue Apr 25 14:46:16 2000

"Bill Sudbrink" <bill_at_chipware.com> wrote:
> Hi,
>
> I have a pair of 851s in a nice case with power supply.
> They are attached to a Cromemco 16FDC in an IMSAI box
> with a Cromemco ZPU and an Expandoram 64K board. I'm
> using the ROM enable on the 16FDC to drive the phantom
> line. There is a reason for these details...
>
> Here is the problem:
>
> #1 Power up the drives by themselves:
> At the drives:
> 5 volt line reads 4.9
> -5 volt line reads -4.9
> 24 volt line reads 23.9
>
> #2 Power up the IMSAI box:
> At the drives:
> 5 volt line reads 1.2
> -5 volt line reads -0.9
> 24 volt line reads 2.6
> and (needless to say) the drives don't work. The Cromemco
> ROM monitor gives all sorts of errors trying to access them.
>
> #3 Power off the IMSAI box:
> (Same as #1)
>
> #4 Power on the IMSAI box again:
> At the drives:
> 5 volt line reads 5.0
> -5 volt line reads -5.0
> 24 volt line reads 24.0
> and the drives work fine.
>
> What gives? Does this make sense to anybody out there?

Hi Bill
 I've seen latch up problems with data busses being active
before the drivers power came on in some old printers. I don't
think this is your problem. I would more likely suspect a
problem with the power supply. In different states, the
drive draws different amounts of current on this line.
I suspect you'll find that there is a problem with current
or a bad filter capacitor in the supply. Try running the
supply without the drives with a varying load. If it is
the supply this should show it.
Dwight
Received on Tue Apr 25 2000 - 14:46:16 BST