A2091 14Mhz SCSI mod

SpeedGeek

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Hello my fellow AmiBayer's! As you probably know by now, I have developed a nasty habit of hacking my Amiga's with the intention of speeding them up in various ways.

So here is my implementation of the Official C= A2091 speedup mod. The reason I say "Official" is because it's mostly taken from the A2091 service manual. The really nice thing about this hack is that it's a very simple thing to do and a perfect DIY project!

First you need to make sure you have the WD33C93"A" (or the AMD "A" version) SCSI chip on the A2091.

Then following the service manual instructions you cut the trace for the upper 2 pins of JP201. Then you IGNORE the service manual instructions to jumper the lower 2 pins of JP201 and FOLLOW my instructions to jumper the outer 2 pins (Pins 1 & 3) and your SCSI chip should now happily be running from a 14 MHz clock!

I've tested this with C= V6.6 and V7.0 ROM's as well as Ralph Babel's Guru ROM. I recommend the C= 7.0 ROM's or Guru ROM for best performance. Using RSCP I've benchmarked transfers around 3.1 MB/sec on my A2000. Enjoy!

Note: See post #36 for info about the NEW 33C93A_Config tool. The actual transfer rates will vary depending on the speed of the hard drive, ROM's, CPU speed, Buster ZorroII vs. SuperBuster ZorroII and your choice of benchmark program!

Here is the link for all images and downloadable files:

http://eab.abime.net/showthread.php?p=745151
 
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Awesome stuff! It really is all about squeezing every last drop of performance out of every part of the system, isn't it?

(y)
 
Yes Andy, you're dead right & 3Mb/Sec on an A2K is not to be sniffed at.
Most impressive to say the least. (y)

Kin
 
Could this be done to the SCSI controller on the A590 as well? Just curious, as the A2000 and A500 are somewhat related....
 
Works :D

Getting 1,5 MB/ sec with a standard A2000 with Sysinfo.
Shall give it some memory now, see if that speeds it up more.

Edit: Yep, FULLY confirmed, with 8MB of fast ram, 2.4MB/Sec even with 6.6 roms and an 68000 :D
My A2091 has 0MB memory, so that's why it was a bit tad slower on the first test.
 
Works :D

Getting 1,5 MB/ sec with a standard A2000 with Sysinfo.
Shall give it some memory now, see if that speeds it up more.

Edit: Yep, FULLY confirmed, with 8MB of fast ram, 2.4MB/Sec even with 6.6 roms and an 68000 :D
My A2091 has 0MB memory, so that's why it was a bit tad slower on the first test.

Brilliant! :D

Kin
 
@Merlin
Yes, it could be done on the A590 but not quite as easily as the A2091. You would have to cut the trace to clock pin of the SCSI chip and run a couple more jumpers to the 74LS86 to create the 14 Mhz clock. If there is enough interest in doing this and I can find the time I'll make a schematic for this. Of course, some clever A590 owner could easily beat me to it!

@8bitbubsy
That's a very good question! Hopefully, some clever A2090A owner can beat me to answering this question as well!
 
Edit: Yep, FULLY confirmed, with 8MB of fast ram, 2.4MB/Sec even with 6.6 roms and an 68000 :D

Wow, that's awesome! That's about the same speed I get from my A3000s native SCSI, to achieve that on an A2000 is very tasty indeed.
 
Edit: Yep, FULLY confirmed, with 8MB of fast ram, 2.4MB/Sec even with 6.6 roms and an 68000 :D

Wow, that's awesome! That's about the same speed I get from my A3000s native SCSI, to achieve that on an A2000 is very tasty indeed.

Yeah, I'm going to look for more 2091's at our clubday and mod on.
This makes them way faster than GVP controllers, but maybe I can find out how to do it on them.
 
QUOTE FROM AMIGA.ORG:

Today, 08:24 AM

desantii
Amiga Addict!
Join Date: Sep 2009
Location: IL, US
Posts: 228

Re: A2091 14Mhz SCSI mod

Did thsi last night, my transfer rates went from 1.4 to 2.7 mb/s

awesome
__________________
Amiga 2000, 030 55mhz, 26mb ram, Indivision ECS, Megachip
Amiga 4000T, 040 28mhz, 18mb ram ... waiting for Indivision MK2

Another example of how "Your Mileage Will Vary"!
 
Wow, that's awesome! That's about the same speed I get from my A3000s native SCSI, to achieve that on an A2000 is very tasty indeed.

I'm getting 3 MB/sec synchronous transfers on my A3000. You would need a good SCSI II hard drive and a properly terminated SCSI bus in order to use this mode. You can use SCSI prefs from Aminet to enable this mode.
 
Then following the service manual instructions you cut the trace for the upper 2 pins of JP201. Then you IGNORE the service manual instructions to jumper the lower 2 pins of JP201 and FOLLOW my instructions to jumper the outer 2 pins (Pins 1 & 3) and your SCSI chip should now happily be running from a 14Mhz clock!

Hi!

I was going to do the mod to my A2091 when I realized I had once soldered pins for JP201 and the board is still configured for 7 MHz SCSI chip (even if I have an AMD 33C93A installed).

What I can't understand is: if you jumper the outer pins, how is the SCSI chip getting the clock signal? According to the schematics, if you cut the trace between the upper two pins and then leave the center one (pin 2) not connected, the SCSI chip clock input is "floating". How does the whole thing work?
 
Hi!

I was going to do the mod to my A2091 when I realized I had once soldered pins for JP201 and the board is still configured for 7 MHz SCSI chip (even if I have an AMD 33C93A installed).

What I can't understand is: if you jumper the outer pins, how is the SCSI chip getting the clock signal? According to the schematics, if you cut the trace between the upper two pins and then leave the center one (pin 2) not connected, the SCSI chip clock input is "floating". How does the whole thing work?

The schematic is in error so if you jumper the lower 2 pins you actually leave the SCSI chip clock floating!

EDIT:
------------------------------------------------------------
The PCB layout is in error since pin 2 of JP201 is not connected to the SCSI chip clock input. The schematic is in error for showing the 14 Mhz clock output from the 74F32 rather than the 74LS86.
 
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The schematic is in error so if you jumper the lower 2 pins you actually leave the SCSI chip clock floating!

I see, so the clocks are on the bottom pins and the SCSI chip clock input is at the top one, most probably it was an error in board layout. Will try the modification soon, thanks for your explanation!
 
I did this today on an A2091 card thats going in an A2000 I will be sellling, the results are AWESOME! (y)
 

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Yup :) The drive I did that test on was a HP Surestore 2000s but its noisy as hell (sounds like a metal grinder so is probably on its way out). Anyway, I had a look around and found a Quantum Fireball SCSI drive and now all my Install disks and WB 2.0 say "exhd0 Suspend Reboot" :blink:

I doubt the mod has anything to do with this so Im going to dig around for another SCSI drive and try that one, I bet the Quantum is shafted :roll:
 
@Taj

I have a 4.1GB with your name on it =) its yours for postage if you want it =D...

hit me up on PM with some deets buddy and we can make it happen.
 
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