Roland AC-60

[dmeek]

Does anyone have the schematic? The BC-60 is not the same.
I have input but no output from the power amp chip LM4766T.
Not sure if it's dead or just muted

Doug

[mozwell]

http://www.ti.com/lit/ds/symlink/lm4766.pdf
First check, are both power supply rails present to the LM4766T.
What is the voltage on the mute pins (6 and 11).
Check any fuses that might be mounted on circuit boards inside the unit.

[dmeek]

I have both power supply rails. I seems the amp is in mute mode. There is a 4.7k resistor
in series with each mute pin and according to the datasheet a current of >1mA is needed
to turn off mute mode. That wold be 4.7V across those resistors. I have 0V.
This amp has a lot of smd parts = hard to trace. The schematic would help.
Another thing I can check is the headphone jack. Sometimes the main amp is muted
when the phones are plugged in, the phones being driven from an op-amp.

[dmeek]

Problem solved. While looking at the headphone jack I noticed nearby a little button labeled "Mute", pressed in
and an LED beside said button, flashing. I said to myself "What would happen if I were to press that button?"
That's all I have to say.

Doug

[mozwell]

Excellent
We've all been there !

[paleeman]

If you'll ever need the schematic, you know, just in case, then send me a PM.