MiniSport Laptop Hacker - Vol 17, Nov 1993 
Copyright (c) 1993 Brian Mork -- "not to make money, but to keep it that 
way for others, too." 
 
>>> ADMIN 
Remember, you can get copies on disk of any software or text files (in- 
cluding the MLHacker series) I refer to by sending me a disk and SASE. 
I'll put a variety of other MLHacker related goodies on there, too. 
Alternately, contact me using the information in the signature block. 
Please, contribute! 
 
MLHacker is available on the KA6ETB Internet HAM-Server.  Send a message 
to ham-server@grafex.cupertino.ca.us with the single line of text: HELP 
to get access information.  Check the \hamradio\newsletters directory. 
I'm watching for other Packet or Internet archivers who will host the 
MLHacker series. 
 
>>> POWER SUPPLY 
A lot of people have a problem where the computer fails to stay powered 
on.  Two LEDs blink for a second or two and then the computer powers 
down.  One of mine has been having this trouble, too, and I finally had a 
chance to reverse engineer the power supply. 
 
The Minisport power supply pinout to the motherboard is via a 16 pin mini 
scotchflex connector.  Pin 1 is indicated by a white arrow on the power 
supply board.  Reverse engineering was carried backward into the power 
supply only until I was reasonably sure I understood how the circuit was 
suppose to work.  Notice some capacitors seem to be reverse biased.  Sur- 
face mount dielectric capacitors still have the banded end negative, 
right? 
 
Pins 2,5 and 6 are not accounted for yet because of unidentified compo- 
nents.  Pins 5,6, and 10 are the ones with bad voltages either causing my 
problem or as a result of my problem.  What a coincidence, eh?  Here's 
what I've been able to determine.  I'm particularly interested in what 
*your* header voltages are if you have this notorious power-off failure 
mode.  These schematics are not a "sure thing" -- they're determined us- 
ing visual trace following, an ohmeter, and a diode checker.  I'm partic- 
ularly unsatisfied with the Pin 10 circuitry.  Other fixit experts out 
there, please give me ideas! 
 
  S487 1004       bobbin            "-B" 
 .-->|-->|-.----.--~~~~-.----.----.-->|-.---.------ Pin4 (+5v) 
(          |    |       |    |    |     |   | 
 ) P11     |    |       |   \-\   |  100| LB| 
(  H922    | 470|    4.7| -  ^6.8 |    === === 
 ) xformer |   ===     ===   |Znr |     |   | 
(          |    |       | +  |    |     |   | 
           |    /       /    /    |     /   / 
           |                      | 
           |                      .----->|---.----- Pin1 (+5v to only 
           .-- glass diode             S487  |            2nd MB RAM) 
               to Pin10                     === 
               circuitry                     |LB 
                                             | 
                                             .----- Pin3 (GND) 
                                             | 
                                             / 
 
                              A3      bobbin 
 .---------------------------->|---.---~~~---.----- Pin7 (+10v) 
(                                  |         | 
 ) G923                           ===       === 
(  P12                             |         | 
 ) xformer                         /         / 
( 
        A3      bobbin 
 .------|<---.---~~~---.--------------------------- Pin8 (-10v) 
(            |       + |                     | 
 ) G923     ===       ===                   === 
(  P12       | 47    - | 3.3              LB | 
 ) xformer   /         /                     / 
( 
                                                .-- Pin11,13,14 
                                                | 
                                                |     (GND) 
                                                / 
 608C04 
  .--.           bobbin 
  |  |----.-------~~~-------.----.---------------- Pin15,16 (+5v) 
  .--.    |                 |    | 
          .---.         100 |   \-\ 
      1000|   | 0.1        ===   ^ 
         === ===            |    |6.8v 
          |   |             |    | Znr 
          .---.             /    / 
          |                                 | 
          /                           edge  |14 
                                     MB3778 |----- Pin 9 (from computer) 
                               |     (_stby)| 
MIDL -----------.       center |            | 
                |       MB3778 |14 
     +5v(pin4)  / 10k   (_stby)|------------------ Pin 12 (from computer) 
           |    \              | 
           |    /              | 
         1 /    |                     4.7K 
         0 \    |                   .-/\/\--. 
         0 /    /    variable       |       | "-B" 
         K \  --\--> resistor       |      -.--|<- Pin 10 (6.6v when working) 
           /    /                   |     / 
           |    |              10K  |   |<  BV3 
 ---->|----.----.------<\  /---/\/\-.---|   PNP 
    glass  |    |        \/             |\ 
    diode  |    \       ----              | 
   from    |LB  /51K     | CBZ2           | 
   Pin4   ===   \        | NPN         +5v(pin4) 
 circuitry |    /        | 
           |    |        | 
           .----.--------. 
                         | 
                         / 
 
 
MIDL is identified in MLH Vol 14 -- in essence, it is +9v power, deliv- 
ered through a diode. 
 
LP stands for "Little Beige capacitor."  I'm guessing they're 0.01uf by- 
pass capacitors.  They have no markings. 
 
In order to progress further, I need to know the identification of a few 
parts:    "24" - 3pin rectangular SMC, 1/16" x 1/8" 
          "14" - 3pin rectangular SMC, 1/16" x 1/8" 
          "BV3" - 3pin rectangular SMC, 1/16" x 1/8" 
          "CBZ2" - 4tab SMC, looks like fixed volt reg (3 + tab) 
 
   Please provide feedback:  * BBS 1-509-244-9260 
                             * AX.25 KA9SNF@wb7nnf.#spokn.wa.usa 
73, Brian                    * Internet bmork@opus-ovh.spk.wa.us 
