Excalibur Mirage

  • Year: 1997

  • CPU: Hitachi H8/3256 - 10MHz (8-bit Single-Chip*)

  • RAM: 2KB*

  • ROM: 48KB*

  • Programmer: Ron Nelson?

The owner of this computer accidentally used an external 12V AC adapter (the correct one is 9V DC). From that moment on, the computer stopped moving the pieces, showing "STALL" on the display at every attempt. The rest apparently worked fine: the controls responded, the display showed information, movements could be entered via the sensory board, etc.

3 screws are removed from the battery compartment, and then the 7 screws on the bottom cover are also removed. But it is advisable to turn the computer before opening it (in its normal working position).

The top cover is lifted, and the computer is switched on. It is confirmed that the head does not move.

The head is moved manually to its starting position. It is tested again and "Stall" appears on the Display. The 3 cables are disconnected to separate the two parts.

The motherboard is placed in the top cover.

Close-up of the motherboard.

The two DC motors are tested by powering them directly on their terminals (3V is enough). Both motors work correctly.

Hitachi H8/3256 "Single-Chip" Microcontroller.

A 5V voltage regulator supplies the CPU and control electronics. The unregulated input power (9V) is supplied to IC2.

Detail of 2 pieces of aluminium "glued" on IC4 and IC5 (the motor drivers).

Detail of IC2 (MIC29151 5.0), 5V High-Current Low-Dropout Regulator.

The board has quite a few "patches", apparently added at the factory.

Pin 3 (GND) has been cut, in order to insert a 1N4148 diode.

IC2 is removed in order to test it properly and improve its fixation.

IC2 (MIC29151) and IC6 (74HC14) are working properly.

Fault detected on this stage: both ICs are damaged.
IC4=IC5=L293D (quadruple high-current half-H drivers).

Detail of the "patches" in the circuit.
The red wire comes directly from the input power supply (9V).

The two damaged L293Ds are removed. The electrolytic capacitor is also faulty.

Two new L293D and a 1000uF/16V capacitor are installed. A droplet of "Araldit Metals" is used to glue each heatsink.

The motherboard is installed in place.

The computer is now working properly.

But after several tests, I realise that the cables of the electromagnetic head are about to break, as they do not have any kind of protection.

I decide to improve these connections.

Everything is now correct, and the head moves properly throughout its whole travel.

The chess computer is ready!