The Wheels On The Bus Go...

 ..."Cannot try Winchester disks as IEEE bus is not active. Is the IEEE cable connected?"

Stop mocking me...

Dangnabit. After getting so far with the Cifer, I hit a brick wall. The hard disk on this computer is connected via the IEEE-488 bus that permeates the entire unit. Basically, there is a 488 connection from the desktop processor board which then links out to the graphics board, the MC68000 processor board and the SASI controller board. SASI is basically the first version of SCSI. See the most excellent video from RetroBytes for more SCSI history.

Desktop processor board, for processing err...desktops?

The Cifer SASI controller board is really more of an interpreter, since there is a 'real' hard disk controller connected the drive, a Xebec 1410. This then feeds the SASI (see later on) data into the SASI interpreter which then translates it into IEEE-488 data and fires it across the bus.

At least, that's the theory.

Don't get SASI with me young man!

A week or so ago I decided to look more closely at the hard disks. I was disappointed that they didn't seem to work, although it should not be unexpected given their age. I had decided to follow the example of Adrian of Adrian's Digital Basement to see if the head stepper motors could be coaxed into life (see here and here).

To do this, I plugged the drive into power and switched it on. Just before the drive would lock the head stepper motor I quickly turned the knurled knob (no sniggering at the back) and watched to see the result. Interestingly, on both drives I had the same result. A fairly rapid resetting of the head back to a home position. But also, once I had done it a couple of times, it became obvious that the drive heads would, when left alone, do a very small but perceptible 'shuffle' once the drive reached full speed. And it did the same on both.

Incidentally, as part of my fiddling with the units I stripped them down a bit to get all the dust and cobwebs out (foreshadowing). 

The bottom of the drive spindle with brake.
 Splendid.

The Rodime drive board. Lovely.

The other en....ARGHAGAH!!!

As a grown man, I should not be able to make such a high pitched squeal of fright. The vacuum cleaner was summoned..

Anyway, after this slight detour, I went back to the unit and decided to do some chip swapping to see if I could prompt the bus to start working. It did not go well. There are several Z80 processors scattered around this machine so I thought I'd start there with my swapping. Removing chips is normally no big deal. Except when it isn't.

There's still 39 legs. What's the problem?

Unexpected socket replacement in 
the workshop area...

Fortunately, it was fairly easy to repair by soldering an offcut of a component leg to the remaining portion of the original leg that was left. With a new socket installed I put everything back together (or had I?) and tried again.

One step forward...

But then I realised I hadn't plugged the power back into the SASI board. Which I then rectified and plugged power in.

...Two steps back.

AAARGHHH!!!!

(To be continued....)