I have had eleven Conchess Monarchs and four Conchess Ambassadors, and all required repairs.
The problems were with :-
(1) Reed Switches
(2) Light Emitting Diodes (LEDs)
(3) Control Buttons

In particular reed switch failures are commonplace. They make the chess computer unusable, so being able to replace reed switches could become a necessity if you are going to be able to keep your Conchess in good working order.

(1) Reed Switches

Conchess chess computers are now around 30 years old. All auto sensory chess computers of this age tend to suffer from reed switch failures, particularly if they have not been used for long periods.

Reed switches are the sensors under the board surface that react to the chess piece magnet when it is placed onto the square and when it is removed. Each square has a reed switch.

Typically a failed reed switch on the starting ranks (1, 2, 7 and 8) will be obvious when all the pieces are put on the board ready for the game, yet one LED light will not go out. Typically the board will refuse to react to any moves made when it’s sensors are telling it that all the chess pieces are not in the correct starting positions. A failed reed switch on ranks 3 to 6 will be discovered during the game.

You can check all the reed switches and LEDs on a Conchess from the starting position by placing the chess pieces as shown in the photo (right). Note that the h5 LED is not lit and therefore there is a reed switch or LED problem there.

Conchess Ambassador 6 20 x 22

I have come across reed switches which sometimes react to the chess piece magnet and sometimes do not. Repeatedly passing a magnet over the reed switch to free it up and get it registering can work as a temporary remedy. Leaving the chesspieces for several hours in position can also get ‘sticky’ reed switches working again. However faulty reed switches typically move without passing current, you can hear the feint click of the switch.

The reason for reed switch failure is corrosion (oxidation) of the switch contacts which prevents the electric current from flowing. It is normally necessary to replace the switch. Reed switches such as that in the photo (left) could be obtained from Maplin Electronics shops for about 2 (Part no. CL37S) until they ceased trading in 2018. A successor company are trading online.

The printed circuit board (PCB) needs to be removed from the chess computer. A five minute job. This gives easy access to the reed switches as shown in the photos below.

The faulty reed switch must be identified, freed from the PCB with a soldering iron and the replacement reed switch soldered in it’s place. Fiddly but not difficult.

Take care when bending and cutting the reed switch wires. They are delicate and it is fairly easy to pull a wire out of the switch by twisting it too much (see below). Hold the wire with thin pliers on the switch side of where you are bending or cutting it and it will be fine. 

Conchess Monarch Repair  2  10 x 10

(2) Light Emitting Diodes (LEDs)

Before changing an LED try just melting the solder of the joint. On the old chess computers sometimes the solder stops making contact resulting in the LED not lighting.

If this does not work LEDs are relatively easy to change on a Conchess as access is so straightforward. In the photos (right) the screwdriver tip points to the holes where the  LED on g7 has been removed. There is a small white spacer to be replaced and the LED needs to be cut carefully to size (below).


The replacement LED needs to go in the correct way round. Otherwise the light will be off when it should be on, and vice versa.

At first I put the wrong type of LED in g7 of the Ambassador below. As you see it is too bright. The correct type can be identified using one of these testers.


(3) Control Buttons

Another achilles heel of the Conchess machines is the control buttons which run down either side of the board. As corrosion builds up they need a harder and longer press to get a reaction, until they stop working altogether.

The buttons push down on a switch which is made up of a small metal plate, or spring, which presses down onto a tiny metal post soldered into the PCB. In the photo the screwdriver tip is pointing at a post, and the spring I removed is lying next to it. The spring rebounds when the pressure is released.

The button can fail due to oxidation of the surfaces on the top of the post and underside of the spring. This problem can be solved by scraping the surfaces clean. However the posts are fragile and a better solution is to use contact spray, such as Maplin Contact Cleaner. This is a general purpose cleaning solvent which gets rid of the corrosion. Without unsoldering or removing anything just spray between the posts and the springs making sure that the spray gets to the contact surfaces.

Conchess Monarch Repair  1  18 x 18

Typical repair October 2009.

Four reed switches replaced on this Conchess Monarch, which is still on the operating table being tested.

Also the control buttons now all work thanks to contact spray. Just spray some on the springs, get a screwdriver between the spring and the post underneath and make sure some spray gets to both surfaces.

This repair took me three to four hours as f7 teased me and took three goes to replace. A competent repairer would have taken less than half that time.

Screwdrivers to remove the back panel, four wooden rods and module holding panel.
Soldering iron and solder.
Scissors to cut reed switches.
Small pliers/ thin nose pliers for holding reed switches.
Contact spray.
LED tester (not needed this time).
Torch (if your eyes aren’t what they used to be).

If you arrived here looking for other information about Conchess chess computers you may find what you are looking for here -
particularly if you want details of the various program modules and their operating guides.

Click on this link to find - Conchess circuit diagrams.


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