Atari ST Book Troubleshooting Guide

Atari ST Book

Fault-finding for the Atari ST Book. The supply figures, thresholds and registers below are from Atari's hardware specification and the part positions from its schematic, drawing C104446-001 Rev 7.0. Repair experience comes from owners restoring ST Books on the exxos forum in 2024. Routine care is on Atari ST Book General Maintenance and the capacitors on Atari ST Book Capacitor Replacement Guide.

Remove the battery pack and disconnect the adaptor before opening the case.

Supplies

The battery pack and the adaptor feed a common point, the "common power source", through Schottky diodes (CR900–CR902 on sheet 10). Every regulator runs from it. There is no +12 V or −5 V rail as on a desktop ST.

ST Book supplies

Supply	Atari's figure	Made by	Notes
Common power source	8 to 20 V input to the regulators	Battery pack via J901, adaptor via J900	The adaptor is rated 16 V 1.25 A
VCC	5 V ±1%, 1 A steady, peaks to 3 A	MC34063 U904, output capacitor C904	Input current-limited to 1.5 A at 5 V; short-circuit current limited to 3 A
MTR	5 V ±1%, 1 A steady, peaks to 3 A	MC34063 U905, output capacitor C914	Hard-disk motor supply, switched by MTR_PWR_ON
LCD bias	−12 to −17 V, 50 mA (section 10.1); −12 to −16 V (section 10.2.2.3)	MAX634 U1004	Set by the contrast control, R819 on sheet 9; switched by /22ON
VBAK	3 V	Linear regulator, LT1020 U804	Keeps the RAM and clock alive when VCC is off
RS-232 drive	±9 V	MAX241 U206	Generated inside the interface IC; can be switched off by software

Sources: Atari's specification, section 10; part positions from schematic sheets 3, 9 and 10.

Level detectors and the power LED

Three detectors watch the supply. SOURCE LOW trips when the common power source falls below 8.8 V and raises an MFP interrupt. SOURCE DEAD trips below 7.2 V and raises a level 7 interrupt so that the operating system can shut down. POWERGOOD trips when VCC falls below 4.55 V; it asserts reset, turns off the VCC, motor and LCD supplies and leaves the RAM and clock on the backup supply.

Power LED

LED	Meaning
Off	Machine off
Green	On, common power source above 8.8 V
Yellow	On, common power source between 8.8 and 7.2 V
Red	On, below 7.2 V; the system is about to shut down

Source: Atari's specification, section 10.2.3.4.

Batteries

Atari specified an eight-cell NiCd pack or a seven-cell alkaline pack. A full NiCd charge runs the machine for 5 to 10 hours and keeps the RAM and clock for about 100 days. The adaptor charges the NiCd pack in under two hours with delta-V peak detection. Internal rechargeable lithium cells keep the RAM and clock for about 40 hours when there is no other source, and are trickle-charged from the common power source. The schematic shows the backup battery as 6.0 V, and one restorer fitted a holder for two ML2016 cells in its place.

Power and start-up faults

To switch on, hold the power button (lower left of the display) until the LED turns green or yellow; the VCC regulator only stays on once POWERGOOD is established.

Power and start-up

Symptom	Likely cause	Action
Completely dead on pack and adaptor	Input fault, failed converter, or a short on VCC	Check each rail for a short to ground before powering. Check the voltage at J900 and J901 and after the combining diodes. One restorer started a machine with no adaptor by feeding 9.6 V to the battery contacts
LED lights, screen stays blank until the recessed reset button is pressed	Reset timing capacitor C100 (10 µF 16 V) on sheet 2	Replacing C100 cured this on one machine; a second, recapped board of the same revision started normally
Will not start after the machine has been without power	Flat internal backup cells	Press reset after the power button. Replace the backup cells
LED yellow or red, shuts down	Pack below 8.8 V or 7.2 V	Charge or replace the pack, or run from the adaptor
Shuts down as soon as the hard disk spins up	Pack too weak for the motor supply	Atari's power control can turn the motor supply off when spin-up pulls the source too low. Try the adaptor
Clock and RAM lost at every power-down	Backup cells or VBAK regulator U804	Measure VBAK (3 V) with the machine off

Reading the supply in software

An 8-bit converter reads the common power source at 100 mV per step, 2,000 times a second while VCC is on, through register FF9210. A 2.5 V reference is converted at the same time through FF9214 and should read about half scale (128); use it to correct the source reading. The configuration and signals register at FF9200 reports the power switch, lid switch, clock alarm, SOURCE DEAD, SOURCE LOW, modem wake and expansion wake lines, and the LCD control register at FF827E switches the SHADOW chip, main power, LCD bias, RS-232 supply and hard-disk motor.

Display faults

The panel has no backlight, so check it in good light first. The LCD bias supply is switched on and off by software, and Atari recommends turning it off before VCC.

Display

Symptom	Likely cause	Action
Weak picture, vertical lines	Leaked electrolytic capacitors on the LCD panel's board	Replace the panel board's electrolytics; one restorer cut the old capacitors' legs close to the body and then removed the legs. Clean residue from the back of the glass with isopropyl alcohol
Bottom half shows only every other pair of columns	Data buffer on the LCD board (IC2, a 74HC365) for the lower-half data lines LD0–LD3	Compare input and output of IC2 on a scope and replace it. IC3 serves the top half
Nothing visible, machine running	LCD bias off or failed, contrast at one end	Work the contrast control through its range. Check for the negative bias at U1004 and the panel connector J301
Contrast control has no effect	MAX634 bias circuit or R819	Check the bias voltage against Atari's −12 to −16 V range before condemning the panel

The panel is driven as upper and lower halves in parallel, four data lines each (UD0–UD3 and LD0–LD3 from the SHADOW chip), so a fault confined to one half points at that half's data path.

Boot faults

Four bombs at boot

The factory TOS needs a working, partitioned hard disk or a floppy drive to boot; with a dead disk it shows four bombs. A corrupted TOS EPROM gives the same result, and replacing the EPROM cured one machine. Patched ST Book TOS images that boot without a disk exist.

Hard disk

The original Conner drives are failing with age; on one machine the drive's seal had liquefied and leaked into its bracket. A CompactFlash card on a 2.5-inch IDE adaptor works as a replacement. Partition it with BOOKFMT.PRG from the ROM disk, drive P:; a 512 MB card worked where a 4 GB card failed.

Storage and ports

Storage and ports

Symptom	Likely cause	Action
External floppy will not work	Wrong cable	The Pseudo-ACSI port carries the floppy-controller signals and adaptor voltage as well as ACSI. Conversion to plain ACSI is a passive cable
High-density disks fail	Configuration bit 6, or FDD_DENSE_SEL	Bit 6 of the configuration register says whether a 16 MHz 1772 is fitted; FDD_DENSE_SEL selects 8 or 16 MHz
Serial port dead	RS-232 supply switched off, or the MAX241	Check the RS232_OFF bit in the LCD control register and the MAX241 at U206 with its charge-pump capacitors C231–C234
MIDI dead both ways	ACIA U200 or its 500 kHz clock	MIDI is a 31.25 kbaud current loop from an HD6350 clocked at 500 kHz
Keyboard dead	Keyboard ribbon, or the COP888CG controller U703	Check the row and column connectors J700 and J701 on sheet 8
Vector Pad erratic	Pad sensor or comparators	The pad's force-sensing inputs go through LP339 comparators U700 on sheet 8

Bit 5 of the configuration switch register (DIP switch SW400 on sheet 11) selects self test or bypass.

Related pages

• Atari ST Book
• Atari ST Book General Maintenance
• Atari ST Book Capacitor Replacement Guide
• Atari STBook Hardware Specification
• Atari STBook Schematic