The Xerox-820

[fgentges at mindspring.com]

Alberto,

The Big Board was designed from scratch by Ferguson and was known as the 
Ferguson Big Board.  I bought one of the first, built it and it was 
great.  Xerox bought the rights, put 5 1/4 drives on it with a small 
tweak to the BIOS known as PFM.

Xerox's change to the hardware caused the heads to momentarily load on 
power up.  The bad part was the WRITE command was also energized 
momentarily.  This caused any disk in the drive to trash a small portion 
of the disk, usually the boot sector.

After much tracing I found it and solved the problem with two pull up 
resistors on a 3 state gate that kept it from the momentary trashing 
problem.  I passed this fix around and many Xerox 820s were fixed. 
Unfortunately, the company and stores did not put in the fix and 
customers were dissatisfied with their 820s and it was one reason they 
killed the program.

This did not afflict the 8 inch drives.  I still have my Ferguson Big 
Board with 8 inch drives and it booted last time I tried it.

Frank K0BRA


On 6/9/2012 3:48 PM, Alberto di Bene wrote:
> On 6/9/2012 12:13 AM, andre kesteloot wrote:
>>
>> /Those of you who have followed our experiments for many, many years,
>> may recall that we used to buy
>> second-hand Xerox-820 boards. Here is what Wikipedia says of those
>> 820-II, and programed in CP/M/
>
> Do I recall correctly in saying that the so-called "Big Board" kit was a
> derivation from the Xerox 820 ?
> Here in Italy a Big Board PCB was bought by a local ham, then he split
> in the thickness dimension the
> PCB, photocopied the two halves, made from the copies two masters, and
> produced a limited series
> of the original PCB, which he sold for the cost to local hams and friends.
>
> I have one complemented with two Seagate 8 inches floppy drives, still
> working.  Well, I guess it's still working....
> Last time I powered it up was almost 15 years go....
>
> I used on it CP/M 3.0, with the BIOS modified (by me) for a sector size
> of 1024 bytes, instead of the original 256,
> and this increased a lot the capacity of each disk.   ... and made them
> incompatible with the rest of the world....  :-)
>
> 73  Alberto  I2PHD
>
>
>
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