amp9 stopped working - help please

[tuo]

The LED needs anyway a series resistor to limit the current through it. So all you'll need is a simple resistor. The value can be calculated for example here:
http://www.ledtuning.nl/index_site.php?Name=calculator

If the LED is too bright, then switch the resistor to another one with higher value. Or if it's too dim, then replace the resistor with lesser valued resistor.

[Scratchy]

You could use a small TO-92 size mosfet to switch the LED on using the 12V PS.
The gate of the mosfet would go on the output of the existing 5V LED pin.
The LED would go across the Drain of the Mosfet to the 12V rail, using a series ballast resistor as Tuo has mentioned.
Have a look at this circuit:
http://brunningsoftware.co.uk/FET.htm

In this case both the LED and the mosfet gate are driven from the same 5V source.
In our case the LED would be driven from the 12v supply and the mosfet gate from the 5V LED source pins.

[T-man]

Thanks for the feedback. However, I guess this won't work either since the 5V LED pin on my board is what's broken. Or have I misunderstood you?

Tuo thanks for the link. Its great.

[V-bro]

The led for HMUTE is driven by IC3 from pin 7 through R11, that's the one not working right? IC3 is a simple Cmos kind of chip that can turn the output ports high or low with sufficient current to drive a led directly, and so it does.

I am not entirely certain what input pins it gets triggered by, could be a couple of them, could be that the output is pulled down for some reason other than the logic output of the TA4100A not working or logic inputs or output on IC3 not working. It could be as simple as a little short from a little solder blob that pulls it down...

Only way to tell for certain is to measure it all the way through, resistance to ground and other pins, voltage on the input pins etc. etc. And it couldn't hurt to check the datasheet of IC3 for the whole pin-out and logic operations.

http://www.alldatasheet.com/datashee...S/74HC365.html

This should help:

[T-man]

Thanks a lot v-bro. I'll give it a go.