Joytech AV Modifications

My modded switch box:

Relay switching of pin 8, (widescreen switching).

Relay switching of RGB and composite signals.

Reduction in the brightness of all LEDs.

Relay Switching

The 4052 that's used for widescreen switching is U5. Isolate pins 11 to 15 either by cutting tracks or removing resistors. Feed 5v into pin 13. The outputs of U5 will then have 5v on them depending on what is selected on the switch box:

1: pin 12

2: pin 14

3: pin 15

4: pin 11

These four pins then power the white relays via a darlington array, (the black chip on the left hand board in the picture above). Note the four resistors to hold the darlington array inputs low when there's no 5v signal there. These darlingtons also drive the RGB switching relays, (a later addition, hence the separate board).

White relay, (SPST):  Maplin code: JH12N

Blue relay, (DPST): Maplin code: JH15R

Darlington driver: ULN2003A : Maplin code: AD93B

Note that there's both 5v and 9v within the switch box and you'll need 5v to drive the relays above.

The relays switch the following SCART pins:

8, (widescreen switching)

15, (Red)

11, (Green)

7, (Blue)

20, (Composite) - which goes to pin 19 on the output connector.


Alternative, (non-relay), widescreen switching fix:

Replace or bridge the following resistors with a bit of wire:

R74, R76, R78, (all near U5), and R77, (near U4).

If you're lucky this is all you'll need to do as the switching signal will now only be slightly out of spec. If not then try a 12V mains adapter as this will reduce the switching resistance of the chips. Unfortunately this may well also adversely affect picture quality - try it and see.

If this is still a no-go then: 'piggy-back' another 4052 IC over the top of U5, matching pin for pin. You don't have to worry about pins 1-5 if you don't want to as they're used for pin 16, (RGB select), signalling which works fine.