Osborne Executive Troubleshooting Guide

Osborne Executive

Fault-finding on the Osborne Executive. The fault trees are Osborne's own, from chapter 9 of the Osborne Field Service Manual. The messages and their meanings come from Osborne's Executive Error Message Listing and the dealer diagnostics from the Diagnostic Procedures. Like the Osborne 1 material, the trees work at the level of field-replaceable units: logic board, memory board, drives, monitor, keyboard and power supply.

Safety

• The Executive contains a CRT, which can hold a dangerous charge after the machine is unplugged. Read CRT Discharge Procedure before working near the tube, its anode cap or the flyback.
• Some of Osborne's checks need mains power on, and the manual warns to use extreme caution for them.
• Do not remove or fit any component, or connect or disconnect any plug or cable, with the power on unless the procedure says so, and note every cable's orientation before disconnecting it.

Before you start

Disconnect the printer, external monitor and modem and test again. If the fault goes away, test the external device and its interface; if not, use Osborne's diagnostics and the trees below.

Osborne's Executive diagnostic diskette tests the logic board, the memory board, the drives, the screen (test patterns) and the keyboard. The logic board tests cover the two serial ports, looped back to each other at 19,200 and 9600 baud through the two channels of the Z80 SIO; the IEEE-488 port; video and attribute RAM in bank 7; the ROM's RAM in bank 6; the ROM checksum in bank 8; and bank uniqueness. The memory board test covers bank 0 (64K) and bank 1 (60K). The port tests need RS-232C and IEEE-488 loopback plugs.

Osborne's quick troubleshooting guide

The first page of chapter 9 is a short table of checks for problems seen in the field, several of them self-inflicted during assembly:

Quick troubleshooting guide, Field Service Manual chapter 9

Problem	Osborne's action
No power to the computer	Check the power panel and power supply fuses. Check the DC harness, AC power panel and power switch for loose or faulty connections. Check the supply's AC input and DC output.
No sign-on message	Check the P12 connector for shorted pins, the braided logic-board ground, the video harness connections, and the copper/mylar insulator for shorting to the logic board.
Drives will not boot	Check the keyboard connector pins, the drive cable connections, the DC input connector and voltages to the logic board, shorted IC pins or P12 wire-wraps, and the braided logic-board ground.
Power switch reversed	Rewire the switch.
Warning message at power-up	Check the installation of the copper/mylar shield on the main logic board.
Drive lights stay on	Check the drive cable connections at the logic board and the drives, then replace the drives, then the logic board.

ROM messages at power-up

The Executive's ROM displays five messages:

Executive ROM messages

Message	Meaning
PERFORMING SELF-TEST	The power-on diagnostics are running.
COMPUTER NOT WORKING PROPERLY / PLEASE CONTACT AN OSBORNE DEALER / PROCEED AT YOUR OWN RISK!	The machine has failed some part of the power-on diagnostics. The message does not say which.
LOADING SYSTEM	The boot is in progress.
DISK IS NOT A VALID SYSTEM DISKETTE. PRESS RETURN TO TRY AGAIN.	There is no valid operating system on the system tracks of the diskette.
BOOT ERROR. PRESS RETURN TO TRY AGAIN.	A hard (unrecoverable) disk error during the boot.

A machine that reaches "DISK IS NOT A VALID SYSTEM DISKETTE" has passed its self-test and read the diskette; look at the media first. A machine that shows the warning message has failed its self-test; Osborne's quick guide points first at the copper/mylar shield on the logic board; after that, the diagnostic diskette tests the logic board and memory board separately.

Disk error messages

When the BIOS meets an error reading or writing a diskette it displays "BIOS error reading drive X:" or "BIOS error writing drive X:", followed by one or more of not-ready, write-protected, fault, not-found, crc-error, lost-data, drq and busy, and a code in the form (code = AA/BB-CCCCCCCCCCCCCCCC).

Hexadecimal codes in a BIOS disk error

Field	Meaning
AA	Floppy disk status, the version shown by the words in the message
BB	Number of sectors attempted in this transfer
CC	The ROM's internal table: byte 1 memory bank; bytes 2 and 3 DMA address; byte 4 starting sector; bytes 5 and 6 current track; byte 7 internal unit number; byte 8 media flag

The machine then asks "Retry this operation (Y or N)?". On a retry it checks the media-change flag. If the diskette has been changed it warns "WARNING: data on disk inserted may be destroyed. Continue (Y or N)?", and Osborne's listing says that if the diskette has been changed and the retry goes ahead, the directory will be destroyed. Answer N unless the original diskette is back in the drive.

"BIOS error device ... not ready, unassign this device (Y or N)?" means output was sent to a logical device, usually the printer on LST:, whose physical device is not connected. It is not a fault in the computer. Connect the device and answer N; answering Y unassigns the device, which must then be reassigned with SETUP or the CP/M DEVICE utility.

The listing also covers CP/M Plus, utility and application messages (WordStar, MailMerge, SuperCalc, SuperData Interchange, CBASIC and MBASIC). Osborne compiled it "to assist you in defining a hardware problem from a software/applications related problem", so check a message there before opening the machine.

DC connector check

Osborne Executive DC connector, section 9.1.1.6

Pins	Output	Minimum	Maximum	Ripple
1 and 7	+12 V	+11.40 V	+12.60 V	150 mV p-p
2 and 6	+5 V	+4.75 V	+5.25 V	50 mV p-p
3 and 5	Common
4	−12 V	−11.40 V	−12.60 V	150 mV p-p

Measure pins 1 and 7, pins 2 and 6, and pin 4, each against pins 3 and 5. All within limits: the AC and DC systems are working. All missing: replace the 1 A 250 V power supply fuse. One missing or out of tolerance: replace the power supply. Check the supply with and without a load; a large difference may mean a short circuit in one of the modules.

Power problems

System does not power up

1. Make sure the power switch is on. Switch off, wait 15 seconds and switch on again. If the machine beeps and the drive lights flash but the screen stays blank, go to the CRT section.
2. Check the mains supply, 115 V or 220 V as applicable.
3. Switch off and test the AC power panel fuse. Replace the fuse or the AC power panel if necessary.
4. Check all cables for breaks and bad connections, and the DC connections at the supply (each connector is keyed).
5. With power on, measure at the DC connector as above.

The AC power panel fuse is 2 A 125 V fast-blow for 115 V and 1 A 250 V fast-blow for 220 V.

Reduced screen display or slow-running disk

Check the DC voltages with all harnesses connected. Out of tolerance: replace the power supply. In tolerance: disconnect the internal monitor and connect an external one. If the external monitor is fine, replace the internal monitor; if the problem continues, replace the logic board.

Disk drive errors during applications

Check the DC voltages. Out of tolerance: replace the power supply. In tolerance: go to the disk drive section.

Disk drive problems

Run the dealer diagnostics program first.

No power at a drive motor

Check the DC voltages and the supply, then the voltages at the harness connector. If they are out of tolerance, replace the harness.

Boot read error

Check that the software suits the hardware and that all connectors and harnesses are in place and undamaged. Clean the head without disturbing the drive's alignment or position, using a head cleaning diskette (for no more than three seconds), 97 % isopropyl alcohol or head cleaner only.

1. If one drive will not boot, try the other. If the other boots and both drive lights are on, check the jumpers and that the terminator resistor is in drive A only. Drive A is jumpered HM and DS1 and has a resistor in socket R21; drive B is jumpered HM and DS2.
2. If the other drive boots, disconnect the internal monitor and connect an external one. If the drive then boots, replace the internal monitor.
3. If it still does not boot, swap the drives, keeping the jumpers and terminator correct for each position.
4. If the error moves with the drive, align or replace that drive. If it does not, replace the drive harness, then the logic board.

If neither drive boots, check the keyboard and its cable, then boot each drive with another diskette. If neither boots, try an external monitor: if one or both drives then boot, replace the internal monitor. If neither boots with the external monitor, replace in turn the drive harness, the logic board, and then replace or align both drives.

Drive not ready

Check all connectors. If the other drive boots, swap the drives, checking jumpers and terminator. If the error does not move with the drive, replace the drive harness; if it moves, replace the logic board.

CRT malfunctions

Wavy screen

Check the supply voltages. Out of tolerance: replace the power supply. Wavy only while a drive is running: replace that drive. Voltages good and drives working: replace the monitor.

Screen not centred

If the raster is tilted, replace the monitor. The Zenith monitor's brightness, contrast, focus, vertical size and horizontal width and phase adjustments are in section 8.4.0; they need the Executive diagnostics diskette, five minutes of warm-up and a non-metallic tool.

Blank screen

1. Turn brightness and contrast fully clockwise.
2. Check the video harness connectors at the monitor and the logic board.
3. Switch off and check that the external video jumper is connected properly.
4. Switch off and, with the logic board video connector attached, replace the video jumper.
5. Check the supply voltages and replace the supply if they are out of tolerance. If the screen stays blank, replace the monitor, then the logic board.

Gaps in the sign-on message

Check the supply voltages and replace the supply if they are out of tolerance. If the gaps continue, replace the logic board.

Flashing sign-on message

Do not confuse it with a vertical hold fault. Press RESET to reboot, then disconnect the keyboard cable. If the flashing stops, replace the keyboard cable; if it continues with a new cable, replace the keyboard.

Keyboard malfunctions

For an individual key: run the keyboard diagnostics, disconnect and reconnect the keyboard cable, check the keyboard connector on the logic board for bent or broken pins, then replace the cable, the keyboard and the logic board in turn. For a complete keyboard failure, or characters that do not match the keys struck: replace the cable, then the keyboard, then the logic board.

Logic and memory board problems

Check the main logic board jumpers against Osborne's table on the Osborne Executive page before replacing either board.

Continuous beep at power-up

Disconnect the keyboard. If the beep continues, replace the memory board, then the logic board. If it stops, replace the keyboard cable, then the keyboard.

Scattered video display

Check the supply voltages. If they are within tolerance, replace the external video jumper, then the memory board, then the logic board.

Memory error during the diagnostics

Check the supply voltages. If they are within tolerance, replace the memory board.

The positions of the CPU, SIO, PIAs, disk controller, ROM and static RAMs, from Osborne's schematic, are on the Osborne Executive page.

RS-232 and IEEE-488 port problems

For no output to the printer or a scrambled printout: check the Setup configuration of the diskette, check Install (WordStar only), check the connectors and interface wiring, use known-good software, try a different printer, check that the printer works, and finally replace the logic board. For a printer that drops characters, go straight from the wiring check to the logic board.

Related pages

• Osborne Executive
• Osborne Executive Maintenance Guide
• Osborne Executive Capacitor Replacement Guide
• Osborne Executive Error Message Listing Feb84
• Osborne 1 / Executive Diagnostic Procedures Jan84
• Osborne Field Service Manual (Revision 2.0)
• Osborne 1 Troubleshooting Guide
• CRT Discharge Procedure