On Oct 4, 22:05, Tony Duell wrote:
> Subject: Gemini Galaxy 2
> I am sure this thing is over 10 years old... I am also almost certain
> that only UK people will have heard of this machine.
>
> I am currently repairing a UK Z-80 machine called a Gemini Galaxy 2. It's
> basically a much-enhanced NASCOM, and uses the same bus pinout but with 3
> more address lines (there's some RAM on the CPU board to handle memory
> mapping).
>
> I have 3 boards in the cardcage - the CPU (Z80 + 64K RAM + boot ROM), an
> IVT (a video card with a Z80 on it) and a floppy controller/SASI
> interface. The latter is linked to a single floppy drive and to a Xebec
> SASI->MFM interface. And that, in turn is linked to a Rodime hard disk.
>
> At the moment, those boards seem to be working. It powers up and asks for
> a boot disk. Which I don't have. Alas the hard disk is not working - it
> starts to spin up and then spins down, and stops with the LED flashing (I
> can get the exact sequence of flashes if anyone has the error code
table).
A common fault on Rodime drives was losing the index sensor output, which
it uses to check the speed as it spins up. I've never found a way of
fixing that completely, since it's a Hall Effect sensor inside the spindle
motor. It generates two pulses per revolution, and the micro uses a
special data pattern on track -2 to decide which is the real index pulse
(it only needs it for formatting, really).
At power-up, the micro checks the RAM and ROM, and then starts the motor
and looks for index pulses. If it sees some, it then checks the speed --
there's a PLL that compares the sensor output to the reference clock
(11MHz, divided down to 120Hz). If the micro doesn't see the index pulses,
it generates "Fault 10" and shuts the system down.
The manual for my RO350 notes that there is one jumper near the
microprocessor which can be removed to circumvent the problem caused by
loss of the special index info on track -2. You could try removing it, if
you have an RO350 or similar.
The two LEDs are for Power and Select; the Power LED flashes for fault
codes. A long flash = 1, short flash = 0.
1 no index track data pattern
2 no flag 0,0 (didn't find Trk0 after 350 steps)
3 motor speed outside 1% (one!) tolerance at end of power-up sequence
4 motor speed outside 10% (ten!) tolerance in normal operation
5 flag zero stays true
6 not used
7 static Write Fault
8 RAM self test failed
9 ROM self test failed
10 no index
11 motor not up to speed
I don't know if these codes are the same on other Rodime drives.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
Received on Sun Oct 04 1998 - 18:03:27 BST