kenc@vaxb.acs.unt.edu (04/16/91)
I thought I'd post my experience with installing the Gemini board in my Mac
Plus.
(BTW, thanks to all those who sent advice, tips, and flames about the
accelerator)
From scratch, I read the installation book through before touching the
screws...I was paranoid about doing something wrong...;)
Anyway, the book seemed rather straight forward. Once I felt comfortable with
the general pattern of events, I grounded myself, and opened the case. (After
brushing aside all the spider webs, and dusting the machine out throroughly, I
figured it could get to work...;)
A while back, I had upgraded the memory in my Plus from 1MB to 4MB of ram. I
had had to cut a resistor on the mother board. The way the Gemini connects,
you need 1MB of ram on the motherboard, and the rest of the extended memory
on the accelerator card. (Since I had 4MB of ram already). It's possible, but
not recommended, to use less than 4MB of ram on the accelerator card.
So, I had to resolder that resistor, pull all the 1MB simms and replaced them
on the motherboard with the 256K simms. Then I moved the 1MB simms over to the
accelerator card. I had to set a jumper to indicate whether the card should be
running at 1 or at 2 wait states. (For my set up, with 80ns memory, I had to
run at 2 waits, if I had 70ns, it would have been and 1). There's also a
jumper that indicates how memory should be accessed.
The next thing was to install the fan/power assembly. It mounts directly over
the floppy, and clips to the power supply board with 4 clips. There were holes
already in the chassis, so it all mounted very easily.
By far the hardest part, I put the Killy clip over the 68000 next. You have to
you a lot of pressure, but you have to be careful NOT to bend any of the pins.
Just make sure that when you start pushing it on, that you don't stop...if you
go back and forth a little bit, you can be sure that a pin or two will bend.
Now that it was securely attached, I fitted the boards together, bending all
pins out of line back into line. I started to test-mount it, to see if it
fit. The bad part is that the chassis must be physically bent to fit the
accelerator card in there. It fits, but it's tight.
You have to trim the battery holder case just a little, so that a ribbon cable
will fit on the inside edge. The battery cover is now history, as the fast
scsi connector replaces it.
Finally, connect the SCSI wires and the power leads to the accelerator, and
gently pry the chassis open. Fit the board in, and bend the chassis back to
hold it. (It's a soft metal, and relatively easy to do.)
Put the case back on, viola!
Next I tried booting off floppy....it worked! Unfortunately, there's no
software to speak of to see any speed difference, so I couldn't tell much as
far as speed differences with a floppy. Okay, no prob, I'm thinking, as I turn
it all off, connect the hard drive, and reboot. *sigh* Sad mac time. Worst
part, it's inconsistent. Sometimes, F0003, others F000A.
Okay....I take a deep breath, pop a few valium, (just kidding), and start
wondering what could cause that..... After preparing to pull my hair out, it
dawned on me that my homemade drives still had the terminating resistors on the
bottom of the drive. Hmmmm....shut down, pull the resistors, BOOM! It boots.
I install the software on the hard drive, and BLAM! 25Mhz, here I come!
Couple of observations: I was nervous as a first time father, and so was
paranoid about the remaining grounded.
Also, no matter how short a time I had turned the mac on, the tube got
charged again VERY quickly. Hence, I had to discharge it after every test.
This is very important!
About the manual: It is VERY clear, easy to read, with lots of pictures, and
the information that I needed was always one page away. Very well put
together over all.
However, the two errors I found: it instructs the installer to put the
SCSI cable in the wrong hole, and it didn't list what the F0003 or F000A sad
mac codes meant. Coulda saved me a little strain there...;)
The difference is incredible. Anyone who desires speed should consider this.
It comes with a 68030 with the MMU inside, and it has a slot for a 68882. The
speed of the board can be taken all the way up to 40Mhz, by simply replacing
the CPU, FPU, and Crystal...! Compared to the standard throughput of the
Plus's SCSI port, it's nothing short of phenominal.
I ordered mine without the coprocessor, so the general overall performance as
measured by speedometer 2.0 was not as good as I'd hoped. However, at 25Mhz,
it beats all macs up to the IIci in CPU speed. The disk speed is right at the
same speed as the IIx, right now, my math speed is abysmal, (But I'm not
running the coprocessor...;)
If you don't need amazing precision, just enough to get the job done, there's
an fp accelerator that's simple amazing. It made the math tests on speedometer
go all the way up to 29.98! About 4-5 times faster than the actual hardware
chips, though HIGHLY inaccurate.
I've heard of horror stories anout incompatibilities with drives. I'm happy to
say that it hasn't caused me any troubles, aside from the terminating resistors
mentioned above. I have a ST296N, and a ST125N, totaling 105MB. They weren't
too pleased with the Plus's standard SCSI, but they really move with the fast
SCSI provided with this card.
I'm told that there are video expansions all the way up to a 2-full-page
display. Unfortunately, it's still b/w. There's still no way to add
color....but for $969 from macZone, it was sincerely worth it!
--
| Ken Corey kenc@vaxb.acs.unt.edu ken@isect.lonestar.org |
| "Ladies strewn, those made to witness his charm, never daring or |
| allowed to touch the man behind the machine." -Leah |