S8000

I got the remains of the original tape drive used in a Zilog S8000. The sender said that it is broken so even when I reassembled it, I still have to find the error somehow.It is now clear, that it is a DEI Series CMTD3400S2



more Pictures

Yesterday I've completed my frontpanel reproduction . The last step was to paint it in a nice fashined black color

Today I got the quiet expensive 1MB memory array and after some warm up phase (damn it's -3°C outside) I tried it out and - look for yourself:

S8000 Monitor 1.2 - Press START to Load System
 
POWER UP DIAGNOSTICS

ACTIVE PERIPHERALS:
WDC

*** ERROR #1002 00 00 10 00 
TCC
ECC

COMPLETE
MAXSEG=<0F>
[

Much bettern then last time - error 1002 means "WDC Drive 0 Error" which is clear because I have no SA1000 drive.

I tried to build up a new front panel over the past days which finally will look like the original one (at least when the front cover is closed).
I sadly don't have all the proper tools (for example no sheet metal folding machine) so I had to work around this as good as I could with the tools I have. The first step:

I found the problem why my WDC board which sent a /BUSREQ all the time and the CPU board which answered with a /BUSACK all the time where not talking properly together.

On the ZBI backplane board are jumpers to leave "slots" on the backplane empty. Normaly the BUS request signals are going as "Bus Acknowledge Out" from one board (starting with the 1st one - the CPU board) to the next board as "Bus Acknowledge In". The next board (an optional "Secondary Serial Board") is not installed in my system so the "Bus Acknowledge Out" which carries the /BUSACK Signal was not going through the 2nd backplane connecter to the 3rd backplane connector where my WDC board is plugged in.

The cause of this problem was a Jumper setting which allows to have the 2nd connector empty (no SSB installed) by rerouting the "Bus Acknowledge Out" signal from the 1st connector to the 3rd connector too. But there where no jumpers on my backplane - someone must have removed them. I reinstalled the missing jumpers and now the boards are coexisting happily together.

Ok, the printed error "0000" means - no external RAM - so the first test the system does is checking if the dRAM is there (which is not because I don't have it )

Today I've built my "custom" frontpanel (just a transition solution) with the remaining stuff I had at home. The "original-like" push button I tried to get in my local electronic distributor was out of stock. So I reused an old circuit board, 11+40 ohm resisitor to get the needed 51 ohm and so on... The final version will contain the "original-like" push buttons, the LED banks and so on. It will be mounted then at the same position where the original panel sits. When it is then hidden behind the front door it will look nearly like the original one. At least, thats the plan. Until then:





After this was done, I've used an old PC-AT PSU for supplying the required power to the backplane ("POWERFAIL" cable ignored):



And then put back all together, huck up a nulmodem cable to my PC and - yeah The firmware got loaded and the usual START message was printed:





Pressing the NMI/START switch on my glamorous frontpanel brings up an immediate FATAL ERROR:

S8000 Monitor 1.2 - Press START to Load System
 
P
*** ERROR #0000     
*** FATAL ERROR
[

I have to look through the disassembled firmware what this could mean - but I don't hope dynamic RAM is tested so early.

Connecting the WDC board to the bus leads to a non-startable system leaving the BUSACK LED on the CPU board permanently on. Probably the WDC is broken and spams the system BUS... But at least this was my first step which was done OK I guess

Over the past days I found out, that the hard disks which where used in the Model 21 where CDC (Control Data Corporation) 9410-24 (24 MB) or 9410-32 (32 MB) models. There model name was "Finch". The disks interface was a Shugart SA1000 Interface and they where connected to the WDC Controller using a so called "FINCH-Adapter board" (described roughly in the S8000 hardware manual) which also includes some logic. I still have no Idea so far which tape drive model was used. It could be some model from DEI using IMFM encoding but someone told me that it might also be QIC-40.... I also found someone having the diagnostig and the ZEUS Installation tapes - He promised doing a backup of them.

The person who successfully bid on ebay on the 1MB DRAM card for around 56 EUR offered me the card for 100 EUR. I declined to pay 100 EUR for it. So He probably takes the card and sticks it to a wall like he intended in the first place...