151 lines
7.7 KiB
Plaintext
151 lines
7.7 KiB
Plaintext
MiniSport Laptop Hacker - Vol 18, Dec 1993
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To discourage pecuniary interests, Copyright (c) 1993 Brian Mork
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>>> ADMIN
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Remember, you can get copies on disk of any software or text file I re-
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fer to (including the MLHacker series) by sending me a disk and SASE.
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I'll put a variety of other MLHacker related goodies on there, too.
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MLHacker is available on the KA6ETB Internet HAM-Server. Send a message
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to ham-server@grafex.cupertino.ca.us with the single line of text: HELP
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to get access information. Check the \hamradio\newsletters directory.
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If you're comfortable with late-night long distance phone calls, you may
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download MLHacker related stuff directly from me at 509-244-9260. Use
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the FILES command, and L)og into the \public\computer directory. Stand-
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ard XMODEM and YMODEM protocols are available. ARO related CD-ROM, In-
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ternet e-mail, and Usenet newsgroups are also available from this free
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service.
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>>> POWER SUPPLY
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Nothing, I repeat nothing, beats a schematic diagram when fixing elec-
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trical equipment. No fancy test equipment can compare. Thank you big
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time, Brian, for 1) recognizing my reverse engineered attempt (see Vol
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17), and 2) sending me the real schematic! Two hours later... I have a
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dead n-channel enhancement-mode MOSFET ("K612" in case anybody can offer
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a cross reference). There's a 7V p-p, 500 KHz square wave arriving at
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the gate. The intent is that the drain pulls current through a switch-
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ing power supply transformer primary. Wasn't happ'ning. Drain stays at
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the +V supply voltage. Comparing with another K612 that handles the
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electroluminescent screen voltages confirms the first one is not work-
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ing.
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Several parts houses couldn't identify the K612 part, so I made a trip
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to Radio Shack and picked up a 276-2072 IFR510 n-Channel MOSFET. It's
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about twice as big as the K612, and its specifications are an over-kill,
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but it's all I had available. It cost just over $2.00. Instead of
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mounting it as a surface mount on the bottom side of the circuit board,
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I layed it sideways between some capacitors on the top of the circuit
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board and ran hookup wire to the bottom side of the board for connec-
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tions. Everything works fine! A representation of the power supply
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pinout given in Vol 5 is in order. This time, I know functionality,
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too.
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With the bottom of the computer removed, the motherboard still in place,
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pin 1 is toward the right and front of the computer, numbered like this:
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15 13 11 9 7 5 3 1
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16 14 12 10 8 6 4 2
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1 5 V backup supply #1, 10-300 mA
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2 BACKUP-ON request from computer, TTL levels
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3 Ground (backup power supplies)
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4 5 V backup supply #2, 10-45 mA
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5 VEE-ON request from computer, TTL levels
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6 -22 V (Vee), 10mA
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7 +10 V, 10 mA
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8 -10 V, 10 mA
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9 EL-ON (LCD screen) request from computer, TTL
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10 Li Battery +V input to power supply (~6.3 V)
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11 Ground (Li battery circuits)
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12 POWER-ON request from computer, TTL levels
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13 Ground (hi current return from pins 15/16)
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14 Duplicates Pin 13
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15 5 V (Vcc), 0.25-0.6 A)
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16 Duplicates Pin 15
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A note of caution is in order. The computer will automatically shut
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down if certain voltages don't come up to specs within a few seconds
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(this appears as a 2 second blink of the power and numlock LEDs and the
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screen). Requests from the computer can be deceiving unless you know
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what you're looking at. For instance, I repeatedly measured Pin 9 at
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zero volts during my debugging. I thought the computer was erroneously
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not asking for the screen voltages. In fact, right when I pushed the
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power button, it came high for a few seconds, and then shut back off.
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It !was! working ok. Pin 12, on the other hand, went high to 5+ volts
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and then dropped back to 4.7 volts as the main 5 V supplies were shut
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down. This pin kept the request (4.7 volts is TTL high) active, and
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only dropped back to zero when I pressed the power switch once again,
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telling the computer to shut "off". Realize if there are good NiCads,
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good Li batteries, or the external charger is plugged in, this computer
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never really shuts totally off.
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There are three main sections to the power supply. The first handles
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all the 5 Volt supplies. Both batteries are brought in to this section
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and the normal computer supply and the backup voltages are provided from
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this circuitry. If pins 1, 4, 15, or 16 are bad at the power supply
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header, this section is malfunctioning.
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The second section is where my trouble occurred. An integrated circuit
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regulator provides oscillation signals for the switching converter and
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appropriate voltage feedback control. A three-tapped transformer fol-
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lowed by diode rectification provides +10v, -10v and -22v. If pins 6,
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7, or 8 are not at correct voltages, suspect problems in this area.
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The last section is associated with the electroluminescent screen volt-
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ages, and has its own 6-pin header. To see it, open up your Minisport
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using the directions in MLH Vol 5 and find the 6-pin jumper going from
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the power supply board into the display pivot joint. Only 4 wires are
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used. One handles ground. Two carry current to/from the brightness
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control, and one is the high voltage drive for the display. Specifical-
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ly:
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6 50-150 VAC p-p, nominally 138 VAC
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5 n/c
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4 GND
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3 n/c
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2 return from 20 Kohm brightness control
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1 diode rectified 10 VDC going to brightness control
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If pins 1 or 6 !of the screen connector! are at incorrect voltages, sus-
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pect problems here. Incidentally, Pin 9 of the motherboard power supply
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connector (see MLH Vol 5 and Vol 17) is a TTL level request from the
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computer to turn the electroluminescent display on. It goes into Pin 14
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of the MB3778. The MB3778 oscillator output is buffered through three
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parallel CMOS gates and toggles the gate of a K612 MOSFET, which in turn
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pulls current through a transformer. Subsequently, a high voltage step
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up transformer (looks like a telephone line isolation transformer) gen-
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erates the high VAC for the screen.
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Packing tape applied on the front and sides of the keyboard worked well
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to bundle the keyboard to the motherboard as I worked on the assembly.
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Without this, the keyboard connector ribbons get severely strained as
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the board is flipped this way then that way.
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I am growing to dislike auto-routed circuit boards. The computer logic
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generates through-the-board vias that terribly confuse a person trying
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to trace the circuitry. In a lot of cases, casual inspection shows sin-
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gle side alternative routes were available.
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>>> BAD ROM DISK
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I received a message over Internet from a Minisport user that indicated
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his ROM disk (C:) has gone dead. He's getting checksum errors on boot-
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up. Do you have the equipment and willingness to pull your ROM, make a
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copy and send it on to Ron? I ask this not just for one user, but ever-
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yone else this will eventually happen to. The source for original ROMs
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has dried up, and if we're going to keep Minisports working, it would be
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good to know who could do this for others.
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>>> MEMORY SWAPS
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The first MB of memory on a ZL-2 is eight discrete chips soldered on the
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motherboard. The second MB is a SIPP package. I know from experience
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the 2nd MB can be unsoldered and swapped into a ZL-1. Thomas asks if
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the lower and upper MB are interchangeable. Unfortunately, no. Howev-
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er, I would be interested in soldering a standard PC SIPP into my ZL-1
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and see if the graft takes. Do you have an unused 1 MB SIPP you'd be
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willing to let me use?
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Please provide feedback: * BBS 1-509-244-9260
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* AX.25 KA9SNF@wb7nnf.#spokn.wa.usa
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* Internet bmork@opus-ovh.spk.wa.us
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73, Brian * 6006-B Eaker, Fairchild, WA 99011
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