[Coco] calling all MM/1 owners

[Gene Heskett]

On Thursday 24 January 2008, Bob Devries wrote:
>I just removed the I/O board from the MM/1 to more closely examine the RTC.
>
>I found that one of the termination resistors for the SCSI bus is oriented
>the opposite way to the other two. RN5, the middle one is different. Now I'm
>wondering what effect this will have on the working of the SCSI bus? Could
>this be my problem?
>
>Joel, the termination resistor's 'notch' or 'dot' end should be in the
>solder pad that's square, am I correct?

I believe so Bob, and if its backwards, you can't cast enough spells and 
sacrifice enough chickens/pigs/virgins to make it work.  We once bought a 
scsi card for an amiga, that had all 3 of them backwards.  It was easier in 
that case to cut and reroute the power and ground lines than to pull them 
from that ultra cheap board and reverse them.

Look at the data line, powered up, with a voltmeter, and do whatever it takes 
to get any resting line above 2.8 volts.  3 is ideal, but by the time you've 
lost .65 volts in the isolation diode between the 5 volt line and the top of 
the resistor packs, 3 can't be done.  This isolation diode can be shorted 
out, which will help considerably IF you can guarantee that there will never 
be a self powered drive cabinet attached to the external scsi connector on 
the back of the card if it has one.  Its there to keep an external supply 
from back feeding into the computer & keeping the 5 volt line up when the 
rest of it, including any cooling fans, is turned off while the drive housing 
is turned on.

The scsi bus IS a transmission line, and MUST be terminated only at the ends 
of the cable, you cannot use one of the plugs 8" from the end of the cable 
and coil the rest up out of the way.

>--
>Regards, Bob Devries, Dalby, Queensland, Australia
>
>Isaiah 50:4 The sovereign Lord has given me
>the capacity to be his spokesman,
>so that I know how to help the weary.
>
>website: http://www.home.gil.com.au/~bdevasl
>my blog: http://bdevries.invigorated.org/
>
>----- Original Message -----
>From: "Dave R in Illinois" <lazyhand at sbcglobal.net>
>To: <coco at maltedmedia.com>
>Sent: Thursday, January 24, 2008 12:03 PM
>Subject: [Coco] calling all MM/1 owners
>
>> Have you checked to make sure the drive / cable is properly terminated?
>> I've
>> seen corroded pins on terminators do strange things to raid arrays. I
>> never
>> owned a mm1 so I am not sure if there even is one, I would assume there
>> would be.
>>
>>
>>
>> -Dave
>>
>>
>>
>> ______________________________________________________
>>
>>
>>
>> I have a small problem with my MM/1, and I'm wondering if there was ever a
>> fix for it?
>>
>> When I power it up, the computer goes through its procedure to try to boot
>> from the floppy, and then from the SCSI hard disc. It *always* locks up
>> the
>> SCSI bus at that point, and pressing reset does not unlock it. I need to
>> cycle the power to unlock it. It then usually fires up correctly, but not
>> always.
>>
>> My MM/1 is a 3MB with the expansion board. It has a 170MB Quantum SCSI
>> drive. The drive itself initialises properly (at least, it makes all the
>> right noises).
>>
>> Comments anyone?
>> --
>> Regards, Bob Devries, Dalby, Queensland, Australia
>>
>> Isaiah 50:4 The sovereign Lord has given me
>> the capacity to be his spokesman,
>> so that I know how to help the weary.
>>
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>
>--
>Coco mailing list
>Coco at maltedmedia.com
>http://five.pairlist.net/mailman/listinfo/coco



-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Don't look now, but the man in the moon is laughing at you.