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From: rubywand@aol.com (RUBYWAND)
Newsgroups: comp.sys.apple2
Subject: Re: SecondSight boot stability
Date: 24 Aug 1996 09:48:44 -0400
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In article <4vfkun$m5s@nnrp1.news.primenet.com>, bpvh@primenet.com
(Bradley P. Von Haden) writes:

>
>
>>Fattening the PS +5V and GND leads cut glitching significantly. On
>>the motherboard, adding #16 gauge wires from the +5V and GND PS
>>connector pads to +5V and GND points on Slots 3 and 7 finished the
>>job. (Second Sight board users may need to fatten the +12V lead,
>>too)  Anyway, no glitches-- the power supply "went good".
>
>
>Is this one of those modifications that if I am not sure how to do it
>I definitely should not try it?
>
>

     That depends on your alternatives. If your GS is bombing regularly
and your setup fits the "power supply problem" profile, then _someone_
needs to do a fix. Maybe the local Apple Users Group could have a Power
Supply Fix meeting. Those familiar with the work required could guide
users through the motherboard and PS leads mods and check their work along
the way.

     Regarding the motherboard additions: Most likely, nobody especially
likes to remove all cords and plugs, remove the Power Supply, pull out
cards, pop out the motherboard-- be sure to undo any hold-down bolts or
nuts-- and do mods. (Also, be sure to mark/label boards & cords and keep
notes of what goes where!)

     Once you've got the MB out, the actual mod is not that bad a job. #16
gauge wire is fairly easy to work with.

     Mainly, you will constantly be worrying about whether or not you are
connecting to the right places. Have a picture or drawing showing the
pin-out for a Slot and have it oriented so that the pin#26/pin#25 end
matches positioning of the MB. Then, since you are working on the bottom
side, remember that left-right is switched.

So: with the MB back facing you, the Slots will be closest to you. Flip
the board over left-right to view the bottom.. On each Slot, The Slot pins
closest to you will be #26 (left) and #25 (right).  #26 (left) is GND; #25
(right) is +5V. The PS connector is just to the left of Slot 1.


Bottom View

________________Front__End________________
|
|
|                                                       SLOT 1            
       
|   
|                                          +12  (50) O  O (1)
|
|            PS Connector
|    
|              O GND
|              O GND
|              
|              O +5
|              O +12
|              O -12
|              O -5                    GND (26) O  O (25) +5              
 
|
|___________Back End ____(viewed from bottom)___


     Use an Ohm meter to verify the above. Check resistance between PS
Connector GND and Pin 26 at each Slot. The resistance should be close to
zero in each case. (The meter may show close to 1 Ohm.)   Mark GND for
Slots 1, 3, and 7 using whiteout or a marker.

     Check resistance between PS Connector +5 and Pin 25 on each Slot.
Check resistance between PS Connector +12 and Pin 50 on each Slot. As
above, resistances should be very low.

NOTE: An Ohm meter passes a small current through the circuit being
measured. If you want to check R from, say, Slot Pin 1 to PS Connector +12
(to verify that Pin 1 is _not_ the +12 pin),  then set the meter for X100.
This reduces the measurement current. By the way, there will be _some_
detectable connection between most circuit points and any of the PS
Connector points. The measured resistances will usually be fairly high.
Depending upon meter lead polarity, the measured resistance from a +5
point to GND may be fairly low; but, it will be significantly different
from zero. In general, avoid doing R measurements on the motherboard
except where you are verifying a likely direct connection.
   

     Check out the empty case. You will get some idea of where supports
crop up to hold the motherboard. When connecting wires from the PS
connector to Slots 3 and 7, remember to leave enough slack to route around
the supports.

     Using a pencil type soldering iron (approx. 25-35 watts) and good
quality solder (like Kester "44)  connect the wires. Avoid using wire with
very thin insulation. It helps to use color-coded leads-- like Black for
GND, Red for +5, and Orange for +12. Run separate leads from the PS
Connector points to each Slot.

Quickie Check (viewing work from back end, bottom):

1. The wires to Slot 3 'look like' the wires going to Slot 7
2. The GND and +5 leads go to the same end of the Slot, the end closest to
you
3. The GND and +12 leads go to the left side of the Slot
4. The +12 lead is on the Slot end farthest from you
5. The +5 lead is the only one on the right side of the Slot
6. The GND leads go to one of the two PS connector points farthest from
you
....  

..........

     Regarding the Fat Power Supply leads mod, as Will Baguhn suggests,
#14 gauge copper is probably heavy enough and it is easier to work with
than #12 gauge. (Someone who has done a fair number of linear PS designs
tends to go for the heaviest gauge that can be bent into place.)  Whether
#12 or #14, try to get stranded stuff for the PS leads. It is easier to
position without having to worry about twisting and breaking loose from
the PS circuit board.


Rubywand