my Data General Nova 4/X, disk woes continue

[Tom Jennings]

>> I suspect the Read/Write Board. So I ordered modern monolithic
>> replacements for the remaining old mono chips from Digikey, and
>> shotgunned all the old electrolytics etc for good measure, in two
>> places electrolytics replaced with tantalums (didn't have
>> ..82uF's).

On Sun, 24 Apr 2005, Allison wrote:

> I hope they are not in any timing circuits.  Another way to
> really shoot ones foot is change all logic and any analog
> stuff or worse digital used as analog.  Newer or older parts
> often will behave different and at 10mhz that was high speed
> then.  There be serpents and devils lurking there.

No timing caps at all. Nearly all the caps were bypass. A few were
DC-blocking. I did replace a lot of .01uF bypass caps with .1uF
caps. All of the analog DC-blocking caps were replaced with same
value, same type. A few bypass electrolytics were replaced with
tantalums of larger value.

>> Formats, reads OK, then errors again! Sheesh! System has been on

> This tells me you've not looked at the cause only apparent problems
> that may not be relevent.

Agreed. It does seem to get worse as it gets warmer (cooling is
all fine though) but I think this is a distraction.

> OK,  the drive uses the same CART as a DEC RL01/02 and the base design
> is a CDC creation if memory serves.  DEC nor DG designed the beast.

Hmm, I thought this was of DG design... this is the "double
density" drive, 10+10, not 5+5... if it's the same as RL01/02 I'd
be very happy!!

> There are two things to pay attention to.  Servo amps for the
> positioner they are analog and can drift.  They must be set up
> at TEMP.  If I remember that varient of the drive also had
> embedded servo information for the head position controls.

Hmm... I only glanced at the servo design, but it's got the usual
diffaction grating plus feedback from the sector headers, I think.
Will have to RTFM.

> The second is the read/write electronics have a PLL for read
> clock recovery.  If thats not set up right it will drift
> outside the lock in range and start tossing errors. It also
> must be setup at working TEMP. The PLL is to track drive
> speed errors and irregularities in position and bit shifting.

Will have to look at this too, after figuring out which would be
first in series with the problem.


> Did you mean "two state amp" or "two stage amp"?  Likely
> it's not an amp problem, a quick look with any old scope
> could check that as it warms up.

Two stage. I think you're right, it's probably not a read amp
issue.