Amstrad PC1512 Maintenance Guide

A Schneider-badged PC1512 DD with its monitor

The Amstrad PC1512 keeps its power supply in the monitor, so most of the work on an old machine falls in three places: the monitor's main board, which carries the supply for the whole computer; the four AA cells that keep the clock and configuration memory alive; and the floppy drives. The system unit itself holds the CPU board, the drives and up to three expansion cards. Amstrad's service manual gives the supply adjustments and the floppy drive procedures used below. Faults are covered in the Amstrad PC1512 Troubleshooting Guide and the supply's electrolytics in the Amstrad PC1512 Capacitor Replacement Guide.

Safety

Warning: the PC-MM and PC-CM contain a mains switch-mode supply and a CRT. Both hold dangerous voltages after the mains lead is removed.

• Unplug the monitor and discharge the tube before working inside it; see CRT Discharge Procedure.
• On the PC-CM, Amstrad marks the power supply area as isolated and tells engineers to take measurements in the supply circuit with reference to the top of C505, "in order to keep the chopper circuit oscillating".
• Fit fuses of the same rating: both monitors use a 3.15 A time-lag mains fuse.
• After working on a monitor, Amstrad's safety test is a 3 kV flash test between the joined mains live and neutral and every accessible metal part, and an insulation resistance of at least 4 MΩ. Amstrad tells engineers to repeat these tests whenever there is doubt about continued electrical safety.

Backup cells

The real-time clock and the 50 bytes of configuration memory (NVR) are kept alive by four non-rechargeable AA cells. No battery power is drawn while the computer is switched on. When the cells run low, the BIOS shows "Please fit new batteries" at start-up and resets the NVR to its default values. DOS Days places the cell tray under the monitor, on top of the system unit.

1. Lift the monitor off and open the tray. Remove old cells at once; alkaline cells left in a stored machine leak.
2. Clean any white or green deposit from the contacts with a cotton bud and white vinegar, then isopropyl alcohol, and dry them; see Battery Explosion, Capacitor or Corrosion Damage.
3. Check that the leads from the tray to the main board are intact. On the PC1640, which uses the same arrangement, leaking cells have run down onto the main board and damaged the CPU socket.
4. Fit four new AA cells and set the clock and configuration. The PC1512's setup program is NVR, run from DOS or from system disc 3 (A:NVR).

Owners run these machines with no cells fitted; the BIOS then shows the battery warning at start-up and the settings are not kept.

Opening the system unit

The case is plastic, with separate metal shields over the main board and the drives; the shields double as drive brackets. The three expansion slots are reached through a removable cover at the back, the "sunroof", without opening the case. An owner of the PC1640, which shares the version 2 case, describes seven screws: two hidden under the stand-offs, two under the plate over the card slots, and three holding the cards. Remove the expansion cover and the card screws, ease the metal card shield away from the plastic and lift the top half.

Clean the case with mild detergent and water, keeping it away from the badges. Blow dust out of the main board shield and the drive bays before power is applied.

Floppy drives

Amstrad treats the floppy drive mechanism as an exchange item, but the service manual includes the drive maker's procedures for the FD-3 (DFC222A) drive: error recovery, parts exchange and adjustments.

FD-3 checks from the service manual (pp. 7–14)

Check	Specification or method
Spindle speed	200 ±2 ms per revolution, measured at TP6
Head cleaning	Lint-free cloth or applicator dipped in 91% isopropyl alcohol
Alignment	Radial track, track sensor, azimuth and index burst checks with a CE diskette
Other checks	Level, resolution, symmetry, write protect sensor

The floppy cable is soldered to the main board and has card-edge connectors for 5.25-inch drives only. The PC1512 does not use a twist in the cable: each drive is set by its own jumper, drive A: to the first drive select (DS0) and drive B: to the second. Owners report 1.44 MB 3.5-inch drives working as drive B: with 720K discs, and Gotek emulators running 720K images. See Floppy Drive Repair for general drive cleaning.

Hard disc

Hard disc models were supplied with a 10 or 20 MB drive; Amstrad lists the 20 MB unit from two suppliers, Xebec (171663/X) and Tandon (171663/T). Amstrad says hard disc units must not be opened. Page 25 of the service manual gives the reinstallation procedure: FDISK, FORMAT and CONFIG from the system discs. Owners replace failed drives with an XT-class hard disc controller, an 8-bit IDE or CompactFlash adapter such as the Lo-tech XT-CF, or an 8-bit SCSI controller. See Hard Drive Maintenance and Repair.

Memory upgrade

The 512 KB PC1512 takes 128 KB more on the main board. Open the case and look at the empty sockets under the left-hand drive bay before ordering chips:

PC1512 memory upgrade (Elliott)

Board	Empty sockets	Chips to fit
Original	Eighteen 16-pin	18 × 4164
Revised	Two 16-pin and four 18-pin	2 × 4164 and 4 × 41464

Use 150 ns or faster parts, fitted with the notch to the socket's notch, then move the LK4 jumper from the left-hand pair of pins to the right-hand pair.

Power supply checks

The supply is adjusted on the monitor's main board. Amstrad lists a digital multimeter, a 0.82 Ω 30 W dummy load and an oscilloscope; the protection step puts the dummy load and an ammeter on pin 11 (+12 V) of the 14-pin DIN plug.

Supply adjustments (service manual pp. 26–27)

Rail	Test point	Target	PC-CM preset	PC-MM preset
+5 V	A	5.10 V ±0.02 V	VR604	VR505
+12 V	B	12.15 V ±0.02 V	VR603	VR504
−5 V	C	5 V ±0.05 V	VR601	VR501
−12 V	D	12.0 V ±0.05 V	VR602	VR502
+12 V protection	Pin 11 of the 14-pin DIN plug	Trip at 4.5 A through the dummy load	VR606	VR507
Monitor +12 V	B	12.0 V ±0.05 V	–	VR503

Amstrad prints the negative rails without their sign in the table. With the computer connected, the rails can also be checked at the 14-way DIN plug: +5 V on pins 3 and 5, +12 V on pin 11, −12 V on pin 9, −5 V on pin 13 and 0 V on pins 2, 4, 8, 10 and 12. Each monitor's table goes on to the picture adjustments: vertical size, brightness, contrast and horizontal hold (15.625 kHz) on the PC-CM; centring, size, linearity, cut-off and contrast on the PC-MM.

The clock is trimmed with TC101 against a timing meter on pin 21 of IC134, set to 0.2 s/day and adjusted to read 0.00. Amstrad says to do this only when the clock chip has been changed.

Keyboard and mouse

The keyboard uses Amstrad's own interface on a 6-way DIN plug, with the keyboard processor (AMS40042) inside the keyboard; standard PC keyboards do not work. Clean the keycaps and case with mild detergent. The Amstrad mouse plugs into its own 9-way socket, and its buttons are read as key codes, so they only work with the KEYB program from Amstrad's system discs.

Checklist for a newly acquired PC1512

1. Remove the AA cells from the tray and clean any leakage.
2. Open the monitor, discharge the tube and look over the supply section for leaking or bulging electrolytics and cracked solder joints.
3. Check the 14-way DIN cable and plug for broken wires.
4. Power the monitor and computer and measure the rails at the DIN plug against the table above.
5. Clean the floppy drive heads and check the drive select jumpers.
6. Fit new AA cells and set up the machine with NVR.

Related pages

• Amstrad PC1512 · Amstrad PC1512 Troubleshooting Guide · Amstrad PC1512 Capacitor Replacement Guide
• Amstrad PC1640 Maintenance Guide
• Amstrad PC1512 Service Manual
• Battery Refurbishment · Recommended Tools