velleman k4700 speaker protection circuit

[cyteen]

I've just been putting this kit together and apart from getting the LEDs round the wrong way initially all went smoothly. However. when I test the unit by connecting PA on the right hand channel to V+ the relay fails to trip. When connecting PA to V- it trips fine. The left hand channel trips for both V+ and V-.

I was hoping someone would point me in the right direction.

 

[Frank Berry]

D4 may be installed backwards.

 

[cyteen]

Thanks for the quick reply, looking at D4 it seems to be consistant with the markings on the top of the pcb. Could I have applied too much heat at some point and killed instead?

 

[moamps]

D4 may be installed backwards.

Or D2 (in some cases).

Thanks for the quick reply, looking at D4 it seems to be consistant with the markings on the top of the pcb...

Repeat test procedure on right channel and measure DC voltage on both side of D4 for +V on input.

Regards,
Milan

 

[cyteen]

D2 also seems consistant with the pcb markings.

Voltage on the end away front the dark band of D4 is + and on the end with the band there is no voltage.

 

[Frank Berry]

Replace D4. It's open.

 

[cyteen]

Many thanks.