Amstrad PPC512 Maintenance Guide

Memory/fuse/volume boards of the PPC512 and PPC640 (service manual p. 18)

The Amstrad PPC512 shares its case, boards, drives and LCD with the Amstrad PPC640, so the routine care of both machines is written up once, in the Amstrad PPC640 Maintenance Guide: batteries and external power, cleaning, the +5 V adjustment, the drives, the screen hinges and the configuration switches. What is particular to the PPC512 is its memory, which can be brought up to 640K as described below.

Before opening the case

The PPC itself runs on low-voltage DC from its batteries, its adaptor or a car lead; the mains voltage is inside the external adaptor. Unplug the adaptor or car lead and take the battery tubes out of the compartment underneath. The time and date are kept by the main batteries, with no separate backup cell, so the clock will need setting afterwards. Amstrad warns against leaving old batteries in the machine, because they can leak and cause damage. For cleaning up after a leak, see Battery Explosion, Capacitor or Corrosion Damage.

Upgrading to 640K

The PPC512's memory board has six unpopulated positions for the 640K upgrade, with their holes filled with solder. MCbx's procedure, from a working PPC512, needs:

• four 41464 DRAMs (64K × 4), -15 or -20
• two 4164 DRAMs (64K × 1), -15 or -20
• sockets for all six, strongly recommended
• a fine-tipped soldering iron and a solder sucker or desoldering braid

Opening the case

1. Do not open the keyboard. Turn the PPC upside down and open the battery compartment.
2. Remove the six large screws.
3. Lift the casing carefully, releasing the catches. There are wires everywhere. Near the rear connectors one catch has to be prised free with a screwdriver.
4. Do not lift the half away: open it like a book towards the connectors, because the speaker and battery cables run to it.
5. Inside are two boards, one inside the other. Take care not to snap the voltage regulator with the large heatsink off the board.
6. Remove the screws holding the boards together, squeeze the three clips while lifting the board slightly, and disconnect the transfer connector that joins the two boards.

The memory positions are on the lower board. It can usually be worked on while still attached by its wires.

Fitting the chips

1. Clear the solder from the six positions one hole at a time with the iron and the sucker. If a hole will not clear, try from the other side, or fill it with fresh solder and try again.
2. Fit a socket with its notch facing the board edge, the same way as the other chips, bend a few pins over on the solder side, and solder it. Check for bridges before fitting the next one.
3. Fit the chips in the sockets.
4. Move the 512K/640K link LK4 on the memory board to the 640K position (MCbx describes LK4 as three pins, with the 512K side closer to the row of eight memory chips), and change the second link on the CPU board. MCbx records a link LK5 labelled 512K/640K whose exact purpose is not known.

Reassembly

Reassemble in the reverse order. The wires running between the halves of the transfer connector have to be pushed clear patiently with a flat screwdriver. If the LCD cable came off, loosen its connector screws, refit it and tighten them again. Switch on and check the memory count reported at start-up.

For reference, Amstrad's parts list for the 640K machine gives eighteen KM41256-15 DRAMs (IC135–IC152) and six KM4164B-15 (IC153–IC158). MCbx's upgrade uses 41464 chips in four of the six empty positions, so read the markings on the board before ordering parts.

Related pages

• Amstrad PPC512 · Amstrad PPC640 Maintenance Guide · Amstrad PPC640 Troubleshooting Guide · Amstrad PPC640 Capacitor Replacement Guide
• Battery Explosion, Capacitor or Corrosion Damage · Floppy Drive Repair · Recommended Tools