Thread: Yamaha XM6150
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John Smith[_12_] John Smith[_12_] is offline
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Default Yamaha XM6150

"John Smith" wrote in message
While waiting for some more TA7317P devices for my previous replair I was
handed a Yamaha XM6150 six channel power amplifier with the channel C
protection light on.

I tried a TIP122/127 pair and The DC conditions then seemed fine.

There's a new 2SD2560 and 2SB1647 in there now.

The protection light is off and all six outputs are only mV from ground.

However the channel C clip light is permanently on (It was on previously
with the shorted output transistors but I didn't thnk much of it at the

I haven't tried a signal yet.

The schematic is in yamaha_xm4220_xm6150.pdf whcih I got from electrotanya.

The channel C clip signal is at pin 3 of CN602 (page 59) and I found 21.6V
there but 25V on the other channels.

Tracing back this comes from R454 on the driver board (also page 59).

There's 0.8V across D410 (cathode +Ve) but only 0.3V across the equivalent
component in an adjacent channel. Q426 has Vbe 0.56V so no surprise it's
turning on. D409 has 0.23V across it (anode +Ve).

Relative to ground both diodes are -60V but that is also true of an adjacent

R457 has 0.340V across it and R460 has 0.343V across it.

moving to Q424/427, Q427 base is 46mV and Q424 base is 35mV.

So now I'm wondering what the quickest way to pinpointing the bad component

Thanks in advance if anyone else would like to have a look at the schematic.

Old guy