64kB EPROM Installation


Static electricity

The module can be destroyed by static electricity. Care should be taken to ground yourself before touching the module or any circuitry in the BBC. Older 74 series logic can be fairly robust to static discharge but CMOS and modern surface mount components are susceptible.

Basic static precautions are simple and free!

Plug in the BBC's mains plug but keep it switched off at the outlet. Then touch the bare metal of the power supply or UHF modulator with a finger. Easy!

Correct orientation

The module can be destroyed by incorrect insertion. Be careful when inserting the module that the pins are aligned correctly and the orientation is correct. Incorrectly inserted/orientated modules may be destroyed and cause damage to your BBC.

Be careful to double check the alignment and orientation when installing upgrades and paged ROMs.






Notch marked on board towards the back of the BBC and cables exit towards the keyboard. EPROM has same orientation as normal ROM socket.



Clips with keyboard installed
27C256-clips1.jpg   27C256-clips2.jpg



Tools needed are a Philips No.2 screw driver to open the case. A Philips or flathead screwdriver (depending on your exact BBC) and a spanner/socket or pliers to remove the keyboard. Tweezers or fine needle nose pliers.

  1. Open the BBC case. Two (large) crosshead screws underneath at the front and two at the back. The lid then hinges up and off at the back.
  2. Remove the bolts holding in the keyboard.
  3. Lift and pull the keyboard forward to expose the ROM sockets (front right). You do not need to disconnect the keyboard wire but may if you want better access.
  4. Connect one long clip wire to the left most pin labelled IC76 pin 12. Connect the second long clip wire to the right most pin labelled IC76 pin 11. Note which colour wire you connected to which signal. Tweezers make it easy to push the connectors on to the header.
  5. Insert the module in a free ROM socket. The pin marked PIN1 should be top left and the writing on the module the correct way up when viewed from the front of the computer. The wires should come out underneath towards the keyboard. (You should not need much force to push the module into the socket - check the pin alignment if it doesn't go in easily.)
  6. Insert a 32kB (27C256) or 64kB (27C512) EPROM programmed with ROM images in the piggyback socket.
  7. Connect the "IC76 pin 12" spring clip to IC76 which is under the keyboard cable. (Pin 16 is top right count clockwise). See photo.
  8. Connect the "IC76 pin 11" spring clip to IC76 which is under the keyboard cable. (Pin 16 is top right count clockwise). See photo.
  9. Bolt keyboard back in and close case.

Accidentally connecting the spring clips to the wrong pins will not cause harm to the module. If the spring clips are disconnected then the EPROM will not work properly and only the high ROM image will be visible but the BBC may well boot. Check that the spring clips do not short circuit to the adjacent pins.

Short jumper wires are provided to connect the ROM selection signals between multiple modules.