The Nimbus PC-186 had an add-on card that was able to control both the floppy drives and internal/external Winchester SCSI drives

To save on production costs, the card was not fully populated if a hard drive(Winchester) was not specified for that build.

Being able to add a hard drive to a Nimbus is a great upgrade for the aging platform.
Here we look at the components that are nessessary to be added to the board.

The missing components

IC11	SN74ALS74AN
IC12	SN74ALS244BN
IC13	SN74ALS374AN
IC14	SN74ALS638A
IC17	SN74ALS08N
IC19	SN74ALS02N
IC20	SN7438N
IC22	SN74ALS21AN
IC24	SN74ALS32N
IC25	SN74ALS74AN
IC26	SN74ALS74AN
IC28	SN74LS14N
C1, 11,12,13,14,15,16,17,18,19, 20,21,23,25,28,30,31,32	22N CAPACITOR
C22,24,27	10UF/10V
RN2	899-1-R150 (4114R-1-151LF - Alternative)
R10	330 ohm
J4	34 PIN H&K
D2,3,4	1N4001
C26	104 e52 100nf

The board requires the holes to be first desoldered.
I chose to socket the new IC's simply because the IC's are sometimes old stock that may or may not work
it also makes changing them in the future easier without stressing the PCB.
I used turned pin DIL sockets as they are more reliable

Hard Drive options are:

Drive

Rodime RO652-20

Seagate ST225N

Seagate ST125N

Miniscribe 8425S-30

Conner CP3020

Seagate ST225NP

Conner CP3040

I went for the Conner CP3040 as its the largest available and I happened to have one to hand.

Parity check must be disabled, certainly on the CP3040, this is done via jumper E4 on the underside of the drive:

For further information on the formatting of the drive please refer to this guide, which although for the SD upgrade
follows a similar path, Click Here

The board that I was converting required that Jumper LK2 was cut:

 

I was unable to source the component RN2 (899-1-R150), which is a bussed 150ohm resistor network, so I produced my own using discrete components
Its not pretty but it works!

After running HDform on the drive, the result was surprisingly good, seems the drive is in good order after all these years:

A few images from the upgrade process: