Roland Cube 80XL question

[Randall]

Came in with no output, bad smell. Found fried 100 watt output IC TDA7293. Replace it. Still no output, but I do find signal is getting to input leg, and I have signal at headphone jack.

I'd like to verify if I have the + and - V's to the IC, but I don't see what they are supposed to be from the schem. And I also find a MUTE AMP function on this IC. My digital chops are not very good, how would one go about determining if this section is working or not? Could it be the mute function is turning off the output? Knowing which direction to go from here would be a big help. Thanks!

I'll try my first pdf edit upload, hopefully it works. CN8 and CN9 are the cable that goes from the main board to the power amp board.

merged.pdf

[52 Bill]

When faced with a chip that I don't know, I search for the data sheet. From the data sheet you will get the pin outs and often a typical circuit that will describe the different functions.

Give it a try.

[Enzo]

You have V+ and V- power supplies. It doesn;t really matter what they are really. The main power supply caps are 63v ones, so I expect the voltages might be 50v or less. Do look on the data sheet, I don't recall what the max is for the 7293. But let us say it is 50v, that means +50 and -50, But if it is instead only +25 and -25, it will still work fine, it just will have less power available. If you get a positive and negative voltage roughly the same, chances are it is OK, there is not a lot of ways for it to be "wrong" anyway. So just look on the power pins, you find some voltage, then it is likely OK. I see fuses in those supply lines, are they OK?

You think it might be stuck in mute? Sure, why not? What is digital about it though? Look for the mute amp control signal on page 2. Is it stuck low? Is Q6 shorted? and so on.

[Randall]

Thank you Enzo! No V's on IC power pins, traced it back to both 2A radial fuses on the rails (F2 and F3) open. Fresh fuses and this one is on the OUT pile.